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19-0784; Rev 1; 7/07
KIT ATION EVALU LE B AVAILA
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
General Description
The MAX8667/MAX8668 dual step-down converters with dual low-dropout (LDO) linear regulators are intended to power low-voltage microprocessors or DSPs in portable devices. They feature high efficiency with small external component size. The step-down converters are adjustable from 0.6V to 3.3V (MAX8668) or factory preset (MAX8667) with guaranteed output current of 600mA for OUT1 and 1200mA for OUT2. The 1.5MHz hysteretic-PWM control scheme allows for tiny external components and reduces no-load operating current to 100A with all outputs enabled. Dual low-quiescent-current, low-noise LDOs operate down to 1.7V supply voltage. The MAX8667/MAX8668 have individual enables for each output, maximizing flexibility. The MAX8667/MAX8668 are available in the spacesaving, 3mm x 3mm, 16-pin thin QFN package.
Features
o Tiny, Thin QFN 3mm x 3mm Package o Individual Enables o Step-Down Converters 600mA Guaranteed Output Current on OUT1 1200mA Guaranteed Output Current on OUT2 Tiny Size 2.2H Chip Inductor (0805) Output Voltage from 0.6V to 3.3V (MAX8668) Ultra-Fast Line and Load Transients Low 25A Supply Current Each o LDOs 300mA Guaranteed Low 1.7V Minimum Supply Voltage Low Output Noise
MAX8667/MAX8668
Ordering Information
PART MAX8667ETEAA+ MAX8667ETEAB+ MAX8667ETEAC+ MAX8667ETECQ+ PKG CODE T1633-4 T1633-4 T1633-4 T1633-4 TOP MARK AEQ AFI AFM AFN
Applications
Cell Phones/Smartphones PDA and Palmtop Computers Portable MP3 and DVD Players Digital Cameras, Camcorders PCMCIA Cards Handheld Instruments
Note: All MAX8667/MAX8668 parts are in a 16-pin, thin QFN, 3mm x 3mm package and operate in the -40C to +85C extended temperature range.
+Denotes a lead-free package.
Ordering Information continued at the end of data sheet. Selector Guide appears at the end of data sheet.
Typical Operating Circuit
IN12 2.6V TO 5.5V 10F IN12 EN1 EN2 REF 0.01F GND IN34 EN3 EN4 OUT3 300mA OUT4 4.7F 4.7F OUT1 (FB1) 14 EN1 15 EN2 16 2.2H LX1 2.2F OUT1 PGND1 LX2 OUT2 PGND2 2.2F 1.2A 1 EN3 2 OUT3 300mA PGND1 13 4.7F LX1
Pin Configuration
TOP VIEW
PGND2 9 8 7 OUT2 (FB2) REF GND EN4 6 5 3 IN34 4 OUT4
12
11
10
MAX8667 MAX8668
MAX8667
600mA 2.2H
THIN QFN (3mm x 3mm)
( ) ARE FOR THE MAX8668
________________________________________________________________ Maxim Integrated Products
LX2
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
ABSOLUTE MAXIMUM RATINGS
IN12, IN34, FB1, FB2, EN1, EN2, EN3, EN4, OUT1, OUT2, REF to GND............................................-0.3V to +6.0V OUT3, OUT4 to GND.....-0.3V to the lesser of + 6V or (VIN34 + 0.3V) PGND1, PGND2 to GND .......................................-0.3V to +0.3V LX1, LX2 Current ..........................................................1.5A RMS LX1, LX2 to GND (Note 1) .......................-0.3V to (VIN12 + 0.3V) Continuous Power Dissipation (TA = +70C) 16-Pin, 3mm x 3mm Thin QFN (derate 20.8mW/C above +70C) .............................1667mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ..................................................... +150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: LX_ has internal clamp diodes to GND and IN12. Applications that forward bias these diodes should take care not to exceed the IC's package-dissipation limits.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN34 = VIN12 = 3.6V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN34 Supply Range IN12 Supply Range IN12 Suppy Range Shutdown Supply Current, IIN12 + IIN34 No Load Supply Current, IIN12 + IIN34 UNDERVOLTAGE LOCKOUT IN12 UVLO IN34 UVLO THERMAL SHUTDOWN Threshold Hysteresis REFERENCE Reference Bypass Output Voltage REF Supply Rejection LOGIC AND CONTROL INPUTS EN_ Input Low Level EN_ Input High Level EN_ Input Leakage Current STEP-DOWN CONVERTERS Minimum Adjustable Output Voltage MAX8668 0.6 V 1.7V VIN34 5.5V 2.6V VIN12 5.5V 1.7V VIN34 5.5V 2.6V VIN12 5.5V VIN12 = VIN34 = 5.5V TA = +25C TA = +85C 1.44 -1 0.001 +1 0.4 V V A 2.6V (VIN12 = VIN34) 5.5V 0.591 0.600 0.15 0.609 V mV/V TA rising +160 15 C C VIN12 rising VIN12 hysteresis VIN34 rising VIN34 hysteresis 1.5 2.4 2.5 0.1 1.6 0.1 1.7 2.6 V V V V VIN12 VIN34 MAX8668, VIN12 VIN34 MAX8667, VIN12 VIN34 VIN12 = VIN34 = 4.2V VEN_ = 0V TA = +25C TA = +85C 0.05 100 150 CONDITIONS MIN 1.7 2.6 2.8 TYP MAX 5.5 5.5 5.5 1 UNITS V V V A A A
MAX8667ETEJS+, all regulators enabled
2
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1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
ELECTRICAL CHARACTERISTICS (continued)
(VIN34 = VIN12 = 3.6V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Maximum Adjustable Output Voltage FB1, FB2 Regulation Voltage OUT1, OUT2 Regulation Voltage FB1, FB2 Line Regulation OUT1, OUT2 Line Regulation FB1, FB2 Bias Current OUT1 Current Limit OUT2 Current Limit OUT1 On-Resistance OUT2 On-Resistance Rectifier-Off Current Threshold (ILXOFF) LX Leakage Current Minimum On-Time Minimum Off-Time LDO REGULATORS Supply Current Output-Voltage Accuracy Line Regulation Dropout Voltage Current Limit Soft-Start Ramp Time Output Noise Power-Supply Rejection Ratio Shutdown Output Resistance TIMING (See Figure 2) Power-On Time (tPWRON) Enable Time (tEN) OUT1, OUT2 OUT3, OUT4 OUT1, OUT2 OUT3, OUT4 25 45 15 35 s s Each LDO 1mA load, TA = +25C 1mA to 300mA load VIN34 = 3.6V to 5.5V, 1mA load VIN34 = 1.8V, 300mA load VOUT3, VOUT4 90% of nominal value To 90% of final value 100Hz to 100kHz, 30mA load, VOUT3 and VOUT4 = 2.8V f < 1kHz, 30mA load 375 -1.5 -3.0 0.003 130 420 0.1 75 57 1 250 465 20 +1.5 +3.0 A % %/V mV mA ms VRMS dB k LX_ = 5.5V TA = +25C TA = +85C -1 0.1 100 50 MAX8668 MAX8668, no load, VFB_ falling MAX8667ETEJS+, no load, VOUT_ falling MAX8668, VIN12 = 2.6V to 5.5V MAX8667, VIN12 = 2.8V to 5.5V MAX8668, shutdown mode MAX8668, VFB1 = 0.5V pMOSFET switch (ILIMP1) nMOSFET rectifier (valley current) pMOSFET switch (ILIMP2) nMOSFET rectifier (valley current) pMOSFET switch, ILX1 = -400mA nMOSFET rectifier, ILX1 = 400mA pMOSFET switch, ILX2 = -400mA nMOSFET rectifier, ILX2 = 400mA 700 500 1333 1200 TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C 0.588 0.582 1.274 1.261 CONDITIONS MIN TYP 3.3 0.600 0.600 1.300 1.300 0.01 0.05 0.1 0.01 900 750 1667 1500 0.3 0.3 0.12 0.12 60 1100 1000 2000 1800 0.6 0.6 0.27 0.27 120 +1 0.612 0.618 1.326 1.339 MAX UNITS V V V %/V %/V A mA mA mA A ns ns
MAX8667/MAX8668
Note 1: All devices are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design. _______________________________________________________________________________________ 3
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Typical Operating Characteristics
(VIN12 = VIN34 = 3.6V, circuit of Figure 4, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 2.8V, VOUT4 = 2.8V, TA = +25C, unless otherwise noted.)
OUT1 EFFICIENCY vs. LOAD CURRENT (VOUT1 = 1.2V)
MAX8667/88 toc01
OUT2 EFFICIENCY vs. LOAD CURRENT (VOUT2 = 1.8V)
MAX8667/88 toc02
OUT1 LOAD REGULATION
1.20 1.15 OUTPUT VOLTAGE (V) 1.10 1.05 1.00 0.95 0.90 0.85
MAX8667/88 toc03
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 ONLY OUT1 ENABLED 0 0.1 1 10 100
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 ONLY OUT2 ENABLED 0.1 1 10 100 1000
1.25
0.80 0 100 200 300 400 500 600 LOAD CURRENT (mA)
1000
10000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
OUT2 LOAD REGULATION
MAX8667/88 toc04
OUT1 OUTPUT VOLTAGE vs. INPUT VOLTAGE (600mA LOAD)
MAX8667/88 toc05
OUT2 OUTPUT VOLTAGE vs. INPUT VOLTAGE (1200mA LOAD)
1.95 OUTPUT VOLTAGE (V) 1.90 1.85 1.80 1.75 1.70 1.65 1.60
MAX8667/88 toc06
1.90 1.80 OUTPUT VOLTAGE (V) 1.70 1.60 1.50 1.40 1.30 1.20 0 200 400 600 800 1000
1.40 1.35 OUTPUT VOLTAGE (V) 1.30 1.25 1.20 1.15 1.10 1.05 1.00
2.00
1200
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SWITCHING FREQUENCY vs. LOAD CURRENT
MAX8667/88 toc07
NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE ALL REGULATOR ENABLED
MAX8667/88 toc08
NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE OUT1 AND OUT2 ONLY
MAX8667/88 toc09
3500 3000 2500 2000 1500 1000 500 0 0 300 600 900 1200 1500 OUT1 OUT2
120 100 SUPPLY CURRENT (A) 80 60 40 20 0 SUPPLY VOLTAGE RISING
120 100 SUPPLY CURRENT (A) 80 60 40 20 0 SUPPLY VOLTAGE RISING SUPPLY VOLTAGE FALLING
SWITCHING FREQUENCY (kHz)
SUPPLY VOLTAGE FALLING
1800
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
LOAD CURRENT (mA)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
4
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1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
Typical Operating Characteristics (continued)
(VIN12 = VIN34 = 3.6V, circuit of Figure 4, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 2.8V, VOUT4 = 2.8V, TA = +25C, unless otherwise noted.)
NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE OUT3 AND OUT4 ONLY
MAX8667/88 toc10
MAX8667/MAX8668
OUT3 OUTPUT VOLTAGE vs. INPUT VOLTAGE (300mA LOAD)
2.95 2.90 OUTPUT VOLTAGE (V) 2.85 2.80 2.75 2.70 2.65 2.60 2.55 2.50
MAX8667/88 toc11
OUT3 DROPOUT VOLTAGE vs. LOAD CURRENT
70 DROPOUT VOLTAGE (mV) 60 50 40 30 20 10 0 0 100 200 300
MAX8667/88 toc12
120 VIN12 = 5.5V 100 80 IIN34 (A) 60 40 20 0 0 1 2 3 4 5 SUPPLY VOLTAGE (V) VIN34 VOLTAGE RISING VIN34 VOLTAGE FALLING
3.00
80
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
900 800 SUPPLY CURRENT (mA) 700 600 500 400 300 200 100 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) IN12 = IN34 2.4 LOAD ON OUT1 3.6 LOAD ON OUT2 NO LOAD ON OUT3 NO LOAD ON OUT4
MAX8667/88 toc13
ENABLE WAVEFORMS
MAX8667/88 toc14
1000
EN1/EN2/ EN3/EN4 VOUT1 VOUT2 VOUT3 VOUT4 IL1 IL2 IIN12 + IIN34 40s/div
5V/div 2V/div 2V/div 2V/div 2V/div
2A/div 2A/div 2A/div
SHUTDOWN WAVEFORMS
MAX8667/88 toc15
OUT1 LOAD TRANSIENT
MAX8667/88 toc16
EN1/EN2/ EN3/EN4 VOUT1 VOUT2 VOUT3 VOUT4
5V/div
VOUT1 300mA
100mV/div (AC-COUPLED)
1V/div 1V/div IOUT1 10mA 10mA 200mA/div
1V/div IL1 1V/div 10s/div 200mA/div
40s/div
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5
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Typical Operating Characteristics (continued)
(VIN12 = VIN34 = 3.6V, circuit of Figure 4, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 2.8V, VOUT4 = 2.8V, TA = +25C, unless otherwise noted.)
OUT2 LOAD TRANSIENT
MAX8667/88 toc17
OUT3 LOAD TRANSIENT
MAX8667/88 toc18
VOUT2 600mA IOUT2 10mA 10mA
200mV/div (AC-COUPLED)
VOUT3
50mV/div (AC-COUPLED)
500mA/div
IOUT3 IL2 500mA/div 0mA
300mA 200mA/div 0mA
10s/div
10s/div
OUT4 LOAD TRANSIENT
MAX8667/88 toc19
OUT1 LIGHT-LOAD SWITCHING WAVEFORMS
MAX8667/88 toc20
VOUT4
50mV/div (AC-COUPLED)
VOUT1
20mV/div
VLX1 IOUT4 0mA 300mA 200mA/div 0mA IL1 500A LOAD 10s/div 10s/div
2V/div
100mA/div
OUT2 LIGHT-LOAD SWITCHING WAVEFORMS
MAX8667/88 toc21
OUT1 HEAVY-LOAD SWITCHING WAVEFORMS
MAX8667/88 toc22
VOUT2
20mV/div
VOUT1
20mV/div
VLX2
2V/div
VLX1
2V/div
500mA/div IL2 500A LOAD 40s/div 500mA/div IL1 500A LOAD 400ns/div
6
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1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
Typical Operating Characteristics (continued)
(VIN12 = VIN34 = 3.6V, circuit of Figure 4, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 2.8V, VOUT4 = 2.8V, TA = +25C, unless otherwise noted.)
OUT2 HEAVY-LOAD SWITCHING WAVEFORMS
MAX8667/88 toc23
MAX8667/MAX8668
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
VOUT3 = 2.80V ILOAD = 100 COUT3 = 4.7F
MAX8667/88 toc24
70 60 VOUT2 20mV/div 50 PSRR (dB) 40 30 20 10 500mA LOAD 0 400ns/div 0.01 0.1 1 10 100
VLX2
2V/div
500mA/div IL2
1000
FREQUENCY (kHz)
OUT3 NOISE
MAX8667/88 toc25
OUT4 NOISE
MAX8667/88 toc26
100V/div
100V/div
VOUT3 = 2.80V ILOAD = 100 1ms/div 1ms/div
VOUT4 = 3.30V ILOAD = 100
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7
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Pin Description
PIN 1 2 NAME MAX8667 EN3 OUT3 MAX8668 EN3 OUT3 FUNCTION Enable Input for Regulator 3. Drive EN3 high or connect to IN34 to turn on regulator 3. Drive low to turn off regulator 3 and reduce input quiescent current. Output of Regulator 3. Bypass OUT3 with a 4.7F ceramic capacitor to GND. OUT3 is discharged to GND through an internal 1k in shutdown. Input Voltage for LDO Regulators 3 and 4. Supply voltage range is from 1.7V to 5.5V. This supply voltage must not exceed VIN12. Connect a 4.7F or larger ceramic capacitor from IN34 to ground. Output of Regulator 4. Bypass OUT4 with a 4.7F ceramic capacitor to GND. OUT4 is discharged to GND through an internal 1k in shutdown. Enable Input for Regulator 4. Drive EN4 high or connect to IN34 to turn on regulator 4. Drive low to turn off regulator 4 and reduce input quiescent current. Ground Reference Output. Bypass REF with a 0.01F ceramic capacitor to GND. Feedback Input for Regulator 2. Connect OUT2 directly to the output of step-down regulator 2. Feedback Input for Regulator 2. Connect FB2 to the center of a resistor feedback divider between the output of regulator 2 and ground to set the output voltage. See the Setting the Output Voltages and Voltage Positioning section. Power Ground for Step-Down Regulator 2 Inductor Connection for Regulator 2 Input Voltage for Step-Down Regulators 1 and 2. Supply voltage range is from 2.6V to 5.5V. This supply voltage must not be less than VIN34. Connect a 10F or larger ceramic capacitor from IN12 to ground. Inductor Connection for Regulator 1 Power Ground for Step-Down Regulator 1 Feedback Input for Regulator 1. Connect OUT1 directly to the output of step-down regulator 1. Feedback Input for Regulator 1. Connect FB1 to the center of a resistor feedback divider between the output of regulator 1 and ground to set the output voltage. See the Setting the Output Voltages and Voltage Positioning section. Enable Input for Regulator 1. Drive EN1 high or connect to IN12 to turn on step-down regulator 1. Drive low to turn off the regulator and reduce input quiescent current. Enable Input for Regulator 2. Drive EN2 high or connect to IN12 to turn on step-down regulator 2. Drive low to turn off the regulator and reduce input quiescent current. Exposed Paddle. Connect to GND, PGND1, PGND2, and circuit ground.
3
IN34
IN34
4 5 6 7 8
OUT4 EN4 GND REF OUT2 --
OUT4 EN4 GND REF -- FB2 PGND2 LX2 IN12 LX1 PGND1 -- FB1
9 10 11 12 13 14
PGND2 LX2 IN12 LX1 PGND1 OUT1 --
15 16 --
EN1 EN2 EP
EN1 EN2 EP
8
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1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
IN34 1.7V TO 5.5V STEP-DOWN IN IN12 2.8V TO 5.5V (2.6V TO 5.5V)
EN UVLO
OUT1
LX1
GND EN
FB
OUT1 (FB1) PGND1
REF
REF AND BIAS
STEP-DOWN IN REF
GND
EN
OUT2
LX2
GND
FB
OUT2 (FB2) PGND2
EN1 EN2 EN3 EN4 IN PWRON LOGIC AND ENABLES EN
LDO
OUT OUT3
OUT3
GND
LDO
IN EN OUT OUT4
OUT4
GND
() ARE FOR THE MAX8668
Figure 1. Functional Diagram
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9
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Detailed Description
The MAX8667/MAX8668 dual step-down converters with dual low-dropout (LDO) linear regulators are intended to power low-voltage microprocessors or DSPs in portable devices. They feature high efficiency with small external component size. The step-down outputs are adjustable from 0.6V to 3.3V (MAX8668) or factory preset (MAX8667) with guaranteed output current of 600mA for OUT1 and 1200mA for OUT2. The 1.5MHz hysteretic-PWM control scheme allows for tiny external components and reduces no-load operating current to 100A (typ) with all regulators enabled. Dual, low-quiescent-current, low-noise LDOs operate down to 1.7V supply voltage. The MAX8667/MAX8668 have individual enable inputs for each output to facilitate any supply sequencing. A UVLO circuit prevents step-down regulators OUT1 and OUT2 from switching when the supply voltage is too low to guarantee proper operation. When VIN12 falls below 2.4V (typ), OUT1 and OUT2 are shut down. OUT1 and OUT2 turn on and begin soft-start when VIN12 rises above 2.5V (typ).
Soft-Start When initially powered up, or enabled with EN_, the step-down regulators soft-start by gradually ramping up the output voltage. This reduces inrush current during startup. See the startup waveforms in the Typical Operating Characteristics section. Current Limit The MAX8667/MAX8668 limit the peak inductor current of the p-channel MOSFET (ILIMP_). A valley current limit is used to protect the step-down regulators during severe overload and output short-circuit conditions. When the peak current limit is reached, the internal p-channel MOSFET turns off and remains off until the output drops below regulation, the inductor current falls below the valley current-limit threshold, and the minimum off-time has expired. Voltage Positioning The OUT1 and OUT2 output voltages and voltage positioning of the MAX8668 are set by a resistor network connected to FB_. With this configuration, a portion of the feedback signal is sensed on the switched side of the inductor, and the output voltage droops slightly as the load current is increased due to the DC resistance of the inductor. This output voltage droop is known as voltage positioning. Voltage positioning allows the load regulation to be set to match the voltage droop during a load transient, reducing the peak-to-peak output voltage deviation during a load transient, and reducing the output capacitance requirements. Dropout As the input voltage approaches the output voltage, the duty cycle of the p-channel MOSFET reaches 100%. In this state, the p-channel MOSFET is turned on constantly (not switching), and the dropout voltage is the voltage drop due to the output current across the onresistance of the internal p-channel MOSFET (RPCH) and the inductor's DC resistance (RL):
VDO = ILOAD (RPCH + RL )
Step-Down DC-DC Regulators (OUT1, OUT2)
Step-Down Regulator Architecture The MAX8667/MAX8668 step-down regulators are optimized for high-efficiency voltage conversion over a wide load range, while maintaining excellent transient response, minimizing external component size, and minimizing output voltage ripple. The DC-DC converters (OUT1, OUT2) also feature an optimized on-resistance internal MOSFET switch and synchronous rectifier to maximize efficiency. The MAX8667/ MAX8668 utilize a proprietary hysteretic-PWM control scheme that switches with nearly fixed frequency at up to 1.5MHz allowing for ultra-small external components. The step-down converter output current is guaranteed up to 600mA for OUT1 and 1200mA for OUT2. When the step-down converter output voltage falls below the regulation threshold, the error comparator begins a switching cycle by turning the high-side p-channel MOSFET switch on. This switch remains on until the minimum on-time (tON) expires and the output voltage is in regulation or the current-limit threshold (I LIMP_ ) is exceeded. Once off, the high-side switch remains off until the minimum off-time (tOFF) expires and the output voltage again falls below the regulation threshold. During this off period, the low-side synchronous rectifier turns on and remains on until either the high-side switch turns on or the inductor current reduces to the rectifier-off current threshold (ILXOFF = 60mA typ). The internal synchronous rectifier eliminates the need for an external Schottky diode. Input Supply and Undervoltage Lockout The input voltage range of step-down regulators OUT1 and OUT2 is 2.6V to 5.5V. This supply voltage must be greater than or equal to the LDO supply voltage (VIN34).
10
LDO Linear Regulators (OUT3, OUT4)
The MAX8667/MAX8668 contain two low-dropout linear regulators (LDOs), OUT3 and OUT4. The LDO output voltages are factory preset, and each LDO supplies
______________________________________________________________________________________
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
loads up to 300mA. The LDOs include an internal reference, error amplifier, p-channel pass transistor, and internal voltage-dividers. Each error amplifier compares the reference voltage to the output voltage (divided by the internal voltage-divider) and amplifies the difference. If the divided feedback voltage is lower than the reference voltage, the pass-transistor gate is pulled lower, allowing more current to pass to the outputs and increasing the output voltage. If the divided feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to pass to the output. soft-start ramp time is typically 100s from the start of the soft-start ramp to the output reaching its nominal regulation voltage.
MAX8667/MAX8668
Current Limit The OUT3 and OUT4 output current is limited to 375mA (min). If the output current exceeds the current limit, the corresponding LDO output voltage drops. Dropout The maximum dropout voltage for the linear regulators is 250mV at 300mA load. To avoid dropout, make sure the IN34 supply voltage is at least 250mV higher than the highest LDO output voltage.
Input Supply and Undervoltage Lockout The input voltage range of LDO regulators OUT3 and OUT4 is 1.7V to 5.5V. This supply voltage must be less than or equal to the voltage applied to IN12 (VIN34 VIN12). An undervoltage lockout circuit turns off the LDO regulators when the input supply voltage is too low to guarantee proper operation. When VIN34 falls below 1.5V (typ), OUT3 and OUT4 are shut down. OUT3 and OUT4 turn on and begin soft-start when VIN34 rises above 1.6V (typ). Soft-Start When initially powered up, or enabled with EN_, the LDOs soft-start by gradually ramping up the output voltage. This reduces inrush current during startup. The
Thermal-Overload Protection
Thermal-overload protection limits the total power dissipation in the MAX8667/MAX8668. Thermal-protection circuits monitor the die temperature. If the die temperature exceeds +160C, the IC is shut down, allowing the IC to cool. Once the IC has cooled by 15C, the IC is enabled again. This results in a pulsed output during continuous thermal-overload conditions. The thermaloverload protection protects the MAX8667/MAX8668 in the event of fault conditions. For continuous operation, do not exceed the absolute maximum junction temperature of +150C. See the Thermal Considerations section for more information.
IN12 tPWRON
tPWRON IS THE PERIOD REQUIRED TO ENABLE FROM SHUTDOWN
ENx
OUTx tEN IS THE ENABLE TIME FOR SUBSEQUENT ENABLE SIGNALS FOLLOWING THE FIRST ENABLE
ENy tEN
OUTy
ENx, ENy ARE ANY COMBINATION OF EN1-EN4.
Figure 2. Timing Diagram
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1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
C3 4.7F INPUT 2.8V TO 5.5V 1.7V TO 5.5V C2 10F IN12 EN1 EN2 REF C1 0.01F GND IN34 EN3 EN4 OUT3 OUT4 C8 4.7F C9 4.7F 300mA 300mA
MAX8667
OUT2 1.2A C7 2.2F L2 2.2H LX2 OUT2 PGND2 LX1 OUT1 PGND1 C6 2.2F L1 2.2H OUT1 600mA
Figure 3. MAX8667 Typical Application Circuit
INPUT 2.6V TO 5.5V
C2 10F
IN12 EN1 EN2 REF
IN34 EN3 EN4 OUT3 OUT4 C8 4.7F C9 4.7F OUT3, 300mA OUT4, 300mA
C1 0.01F GND
OUT2 0.6V TO 3.3V, 1.2A
L2 2.2H LX2 R3 R5*
MAX8668
LX1 R1
L1 2.2H
OUT1 0.6V TO 3.3V, 600mA
R6* C6 2.2F C4 R4 PGND1 PGND2 R2
C7 2.2F for VOUT2 1.8V 4.7F for VOUT2 > 1.8V
FB2 C5 C10*
FB1
*C10, R5, AND R6 ARE OPTIONAL
Figure 4. MAX8668 Typical Application Circuit
12 ______________________________________________________________________________________
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
Applications Information
Setting the Output Voltages and Voltage Positioning
The LDO output voltages of the MAX8667/MAX8668, and the step-down outputs of the MAX8667 are factory preset. See the Selector Guide to find the part number corresponding to the desired output voltages. The OUT1 and OUT2 output voltages of the MAX8668 are set by a resistor network connected to FB_ as shown in Figure 5. With this configuration, a portion of the feedback signal is sensed on the switched side of the inductor (LX), and the output voltage droops slightly as the load current is increased due to the DC resistance of the inductor (DCR). This allows the load regulation to be set to match the voltage droop during a load transient (voltage positioning), reducing the peakto-peak output-voltage deviation during a load transient, and reducing the output capacitance requirements. For the simplest method of setting the output voltage, R6 is not installed. Choose the value of R2 (a good starting value is 100k), and then calculate the value of R1 as follows: V R1 = R2 x OUT - 1 VFB where VFB is the feedback regulation voltage (0.6V). With the voltage set in this manner, the voltage positioning depends only on the DCR, and the maximum output voltage droop is: VOUT(MAX) = DCR x IOUT(MAX)
FB_ R2 L1 LX_ DCR OUT
MAX8667/MAX8668
R1 C4
ESR R6 (OPTIONAL) C6
RLOAD
Figure 5. MAX8668 Feedback Network
Calculate the factor m based on the desired load-regulation improvement: m= IOUT(MAX) x DCR VOUT(DESIRED)
where IOUT(MAX) is the maximum output current, DCR is the inductor series resistance, and VOUT(DESIRED) is the maximum allowable droop in the output voltage at full load. The calculated value for m must be between 1.1 and 2; m = 2 results in a 2x improvement in load regulation. Now calculate the values of R1 and R6 as follows: R1 = REQ x m R6 = REQ x m
m-1
The value of R1 should always be lower than the value of R6.
Setting the Output Voltages with Reduced Voltage Positioning To obtain less voltage positioning than described in the previous section, use the following procedure for setting the output voltages. The OUT1 and OUT2 output voltages and voltage positioning of the MAX8668 are set by a resistor network connected to FB_ as shown in Figure 5. To set the output voltage (VOUT), first select a value for R2 (a good starting value is 100k). Then calculate the value of REQ (the equivalent parallel resistance of R1 and R6) as follows:
V REQ = OUT - 1 x R2 VFB where VFB is the feedback-regulation voltage (0.6V).
Power-Supply Sequencing
The MAX8667/MAX8668 have individual enable inputs for each regulator to allow complete control over the power sequencing. When all EN_ inputs are low, the IC is in low-power shutdown mode, reducing the supply current to less than 1A. After one of the EN_ inputs asserts high, the corresponding regulator begins softstart after a delay of tEN (see Figure 2). The first output enabled from shutdown mode or initially powering up the IC has a longer delay (tPWRON) as the IC exits the low-power shutdown mode.
Inductor Selection
The MAX8667/MAX8668 step-down converters operate with inductors between 2.2H and 4.7H. Low inductance values are physically smaller, but require faster switching, resulting in some efficiency loss. The inductor's DC current rating must be high enough to account
13
______________________________________________________________________________________
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Table 1. Recommended Inductors
MANUFACTURER FDK FDK Murata Sumida TDK TOKO TOKO Wurth Taiyo Yuden INDUCTOR MIPF2016 MIPF2520D LQH32CN2R2M5 LQM31P CDRH2D09 GLF251812T D2812C MDT2520-CR TPC Series TPC Series CB2518T L (H) 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 4.7 2.2 RL (m) 110 80 97 220 120 200 140 80 55 124 90 CURRENT RATING (A) 1.1 1.3 0.79 0.9 0.44 0.6 0.77 0.7 1.8 1.35 0.51 L x W x H (mm) 2.0 x 1.6 x 1.0 2.5 x 2.0 x 1.0 3.2 x 2.5 x 1.55 3.2 x 1.6 x 0.95 3.2 x 3.2 x 1.0 2.5 x 1.8 x 1.35 2.8 x 2.8 x 1.2 2.5 x 2.0 x 1.0 4.0 x 4.0 x 1.1 4.0 x 4.0 x 1.1 2.5 x 1.8 x 2.0
for peak ripple current and load transients. The stepdown converter's unique architecture has minimal current overshoot during startup and load transients and in most cases, an inductor capable of 1.3x the maximum load current is acceptable. For output voltages above 2V, when light-load efficiency is important, the minimum recommended inductor is 2.2H. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50m to 150m range. For higher efficiency at heavy loads (above 200mA) and minimal load regulation, keep the inductor resistance as small as possible. For light-load applications (up to 200mA), higher resistance is acceptable with very little impact on performance.
small and to ensure regulation loop stability. These capacitors must have low impedance at the switching frequency. Surface-mount ceramic capacitors are a good choice due to their small size and low ESR. Make sure the capacitor maintains its capacitance over temperature and DC bias. Ceramic capacitors with X5R or X7R temperature characteristics generally perform well. The output capacitance can be very low. For most applications, a 2.2F ceramic capacitor is sufficient. For C7 of the MAX8668, a 2.2F (VOUT2 1.8V) or a 4.7F (VOUT2 > 1.8V) ceramic capacitor is recommended. For optimum load-transient performance and very low output ripple, the output capacitor value in F should be equal to or greater than the inductor value in H.
Capacitor Selection
Input Capacitors The input capacitor for the step-down converters (C2 in Figures 3 and 4) reduces the current peaks drawn from the battery or input power source and reduces switching noise in the IC. The impedance of C2 at the switching frequency should be very low. Surface-mount ceramic capacitors are a good choice due to their small size and low ESR. Make sure the capacitor maintains its capacitance over temperature and DC bias. Ceramic capacitors with X5R or X7R temperature characteristics generally perform well. A 10F ceramic capacitor is recommended. A 4.7F ceramic capacitor is recommended for the LDO input capacitor (C3 in Figure 3). Step-Down Output Capacitors The step-down output capacitors (C6 and C7 in Figures 3 and 4) are required to keep the output-voltage ripple
14
Feed-Forward Capacitor The feed-forward capacitors on the MAX8668 (C4 and C5 in Figure 4) set the feedback loop response, control the switching frequency, and are critical in obtaining the best efficiency possible. Small X7R and C0G ceramic capacitors are recommended. For OUT1, calculate the value of C4 as follows: C4 = 1.2 x 10-5(s/V) x (VOUT / R1) For OUT2, calculate the value of C5 and C10 as follows: Cff = 1.2 x 10-5(s/V) x (VOUT / R3) Cff = C5 + (C10 / 2) (C10 / C5) + 1 = (VOUT / VFB), where VFB is 0.6V. Rearranging the formulas: C10 = 2 x Cff x (VOUT - VFB)/(VOUT + VFB) C5 = Cff - (C10 / 2)
______________________________________________________________________________________
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
C10 is needed if VOUT > 1.5V or VIN12 can be less than VOUT / 0.65. PD3 = IOUT3 x (VIN34 - VOUT3 ) PD4 = IOUT4 x (VIN34 - VOUT4 ) The maximum junction temperature of the MAX8667/ MAX8668 is +150C. The junction-to-case thermal resistance (JC) of the MAX8667/MAX8668 is 6.9C/W. When mounted on a single-layer PCB, the junction to ambient thermal resistance ( JA ) is about 64C/W. Mounted on a multilayer PCB, JA is about 48C/W. Calculate the junction temperature of the MAX8667/MAX8668 as follows: TJ = TA + PD x JA where TA is the maximum ambient temperature. Make sure the calculated value of TJ does not exceed the +150C maximum.
MAX8667/MAX8668
LDO Output Capacitor and Stability Connect a 4.7F ceramic capacitor between OUT3 and GND, and a second 4.7F ceramic capacitor from OUT4 to GND. For a constant loading above 10mA, the output capacitors can be reduced to 2.2F. The equivalent series resistance (ESR) of the LDO output capacitors affects stability and output noise. Use output capacitors with an ESR of 0.1 or less to ensure stable operation and optimum transient response. Surfacemount ceramic capacitors have very low ESR and are commonly available. Connect these capacitors as close as possible to the IC's pins to minimize PCB trace inductance.
Thermal Considerations
The maximum package power dissipation of the MAX8667/MAX8668 is 1667mW. Make sure the power dissipated by the MAX8667/MAX8668 does not exceed this rating. The total IC power dissipation is the sum of the power dissipation of the four regulators: PD = PD1 + PD2 + PD3 + PD4 Estimate the OUT1 and OUT2 power dissipations as follows: PD1 = IOUT1 x VOUT1 x PD2 = IOUT2 x VOUT2 x 1- 1-
PCB Layout
High switching frequencies and relatively large peak currents make PCB layout a very important aspect of design. Good design minimizes excessive EMI on the feedback paths and voltage gradients in the ground plane, both of which can result in instability or regulation errors. Connect the input capacitors as close as possible to the IN_ and PGND_ pins. Connect the inductor and output capacitors as close as possible to the IC and keep the traces short, direct, and wide. The feedback network traces are sensitive to inductor magnetic field interference. Route these traces away from the inductors and noisy traces such as LX. Keep the feedback components close to the FB_ pin. Connect GND and PGND_ to the ground plane. Connect the exposed paddle to the ground plane with one or more vias to help conduct heat away from the IC. Refer to the MAX8668 evaluation kit for a PCB layout example.
where RL is the inductor's DC resistance, and is the efficiency (see the Typical Operating Characteristics section). Calculate the OUT3 and OUT4 power dissipations as follows:
______________________________________________________________________________________
15
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Ordering Information (continued)
PART MAX8667ETEHR+ MAX8667ETEJS+ MAX8668ETEA+ MAX8668ETEP+ MAX8668ETEQ+ MAX8668ETET+ MAX8668ETEU+ MAX8668ETEV+ MAX8668ETEW+ MAX8668ETEX+ PKG CODE T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 T1633-4 TOP MARK AFJ AFQ AER AFK AFR AFS AFL AFT AFU AFV PART MAX8667ETEAA+ MAX8667ETEAB+ MAX8667ETEAC+ MAX8667ETECQ+ MAX8667ETEHR+ MAX8667ETEJS+ MAX8668ETEA+ MAX8668ETEP+ MAX8668ETEQ+ MAX8668ETET+ MAX8668ETEU+ MAX8668ETEV+ MAX8668ETEW+ MAX8668ETEX+ OUT1 (V) 1.20 1.20 1.20 1.60 1.80 1.30 ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ
Selector Guide
OUT2 (V) 1.80 1.80 1.80 1.80 1.20 1.30 ADJ ADJ ADJ ADJ ADJ ADJ ADJ ADJ OUT3 (V) 2.80 2.85 1.20 2.80 2.60 3.30 2.80 3.30 2.80 3.30 3.30 3.30 3.30 2.80 OUT4 (V) 2.80 2.85 1.20 1.20 2.80 2.70 2.80 1.80 1.20 3.30 2.80 2.50 3.00 1.80
All MAX8667/MAX8668 parts are in a 16-pin, thin QFN, 3mm x 3mm package and operate in the -40C to = +85C extended temperature range.
+Denotes a lead-free package.
Chip Information
PROCESS: BiCMOS
16
______________________________________________________________________________________
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
12x16L QFN THIN.EPS
MAX8667/MAX8668
MARKING
E E/2
(ND - 1) X e
(NE - 1) X e
D2/2
D/2 D
AAAA
C L
e D2
k
b E2/2
0.10 M C A B
C L
L
E2
0.10 C
0.08 C A A2 A1 L
C L
C L
L
e
e
PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
1 2
______________________________________________________________________________________
17
1.5MHz Dual Step-Down DC-DC Converters with Dual LDOs and Individual Enables MAX8667/MAX8668
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
PKG REF. A b D E e L N ND NE A1 A2 k 0.25 0 0.35
8L 3x3 MIN. NOM. MAX. 0.70 0.25 2.90 2.90 0.75 0.30 3.00 3.00 0.55 8 2 2 0.02 0.20 REF 0.25 0.05 0 0.80 0.35 3.10 3.10 0.75
12L 3x3 MIN. NOM. MAX. 0.70 0.20 2.90 2.90 0.45 0.75 0.25 3.00 3.00 0.55 12 3 3 0.02 0.20 REF 0.25 0.05 0 0.80 0.30 3.10 3.10 0.65
16L 3x3 MIN. NOM. MAX. 0.70 0.20 2.90 2.90 0.30 0.75 0.25 3.00 3.00 0.40 16 4 4 0.02 0.20 REF 0.05 0.80 0.30 3.10 3.10 0.50 PKG. CODES TQ833-1 T1233-1 T1233-3 T1233-4 T1633-2 T1633F-3 T1633FH-3 T1633-4 T1633-5
EXPOSED PAD VARIATIONS
D2 MIN. 0.25 0.95 0.95 0.95 0.95 0.65 0.65 0.95 0.95 NOM. 0.70 1.10 1.10 1.10 1.10 0.80 0.80 1.10 1.10 MAX. 1.25 1.25 1.25 1.25 1.25 0.95 0.95 1.25 1.25 MIN. 0.25 0.95 0.95 0.95 0.95 0.65 0.65 0.95 0.95 E2 NOM. 0.70 1.10 1.10 1.10 1.10 0.80 0.80 1.10 1.10 MAX. 1.25 1.25 1.25 1.25 1.25 0.95 0.95 1.25 1.25 PIN ID 0.35 x 45 0.35 x 45 0.35 x 45 0.35 x 45 0.35 x 45 0.225 x 45 0.225 x 45 0.35 x 45 0.35 x 45 JEDEC WEEC WEED-1 WEED-1 WEED-1 WEED-2 WEED-2 WEED-2 WEED-2 WEED-2
0.65 BSC.
0.50 BSC.
0.50 BSC.
NOTES: 1. 2. 3. 4. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. N IS THE TOTAL NUMBER OF TERMINALS. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. DRAWING CONFORMS TO JEDEC MO220 REVISION C. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. WARPAGE NOT TO EXCEED 0.10mm.
5. 6. 7. 8. 9. 10. 11. 12.
PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
2 2
Revision History
Pages changed at Rev 1: 1, 12, 14, 18
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products. Inc.

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