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CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator GENERAL DESCRIPTION
The CM3706A is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version. Supply current with no load is 300uA and drops to <1uA in shutdown. The 2.5V to 6.5V input voltage range makes the CM3706A ideally suited for single Li-Ion, two to four AA battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage.
FEATURES
High Efficiency: Up to 96% 1.5Mhz Constant Switching Frequency 600mA Output Current at VIN=3V Integrated Main switch and synchronous rectifier. No Schottky Diode Required 2.5V to 6.5V Input Voltage Range Output Voltage as Low as 0.6V 100% Duty Cycle in Dropout Low Quiescent Current: 300A Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Short Circuit Protection Thermal Fault Protection <1uA Shutdown Current Space Saving 5-Pin Thin TSOT23 package
APPLICATIONS
Cellular and Smart Phones Microprocessors and DSP Core Supplies Wireless and DSL Modems PDAs MP3 / MP4 Player Portable Instruments Digital Still and Video Cameras
TYPICAL APPLICATIONS
IN 2.5V TO 5.5V
Cin 4.7uF
4
3
2.2uH
VIN
1
SW
634k
OUT
CM3706A RUN GND VFB
2
316K
5
Cout 10uF 22PF
Figure 1. Basic Application Circuit with CM3706A adjustable version
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 1
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator PIN CONFIGURATION
TSOT23-5 Top View
BLOCK DIAGRAM
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 2
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator PIN DESCRIPTION
Pin No. 1 Symbol RUN Description Regulator Enable control input. Drive RUN above 1.5V to turn on the part. Drive RUN below 0.3V to turn it off. 2 3 4 5 GND SW VIN FB Ground Pin. Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the drains of the internal P-CH and N-CH MOSFET switches. Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2F or greater ceramic capacitor. VFB (CM3706A): Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. In shutdown, all functions are disabled drawing <1A supply current. Do not leave RUN floating.
ORDERING INFORMATION/ MARKING
Adjustable Output Version
Part Number CM3706AGIM25
Output Adj
Top Mark A1XY
Temp Range -40C to +85C
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 3
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator ABSOLUTE MAXIMUM RATINGS(Note 1)
Absolute maximum ratings are those values beyond which the device could be permanently damaged. Input Supply Voltage...................................................-0.3V to 7.0V Peak SW Sink and Source Current............................. 1.5A RUN, VFB Voltages .................................- 0.3V to (VIN + 0.3V) Junction Temperature (Note 2) ........... ........................ 125C SW Voltage.............................................. - 0.3V to (VIN + 0.3V) Storage Temperature Range ....................... - 65C to 150C
Operating Temperature Range.....................-40C to +85C
Lead Temperature (Soldering, 10 sec)......................... 300C
OPERATING CONDITIONS
Temperature Range .......................... -40C to 85C Vin Operating Range .........................2.5V to 5.5V
Thermal Resistance (Note 3):
Package TSOT23-5 JA 250C/W JC 110C/W
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: CM3706A : TJ = TA + (PD)(JA) Note 3: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 4
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator
ELECTRICAL CHARACTERISTICS
(Unless otherwise stated, these specifications apply TA=25C; VIN=+3.6V) maximum ratings are stress ratings only and functional device operation is not implied.
Parameter
Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode VFB=0.5V
Conditions
MIN
2.5
TYP
MAX
6.5
unit
V
300 0.1 0.5880 0.5865 0.5820 0.6000 0.6000 0.6000
400 1.0 0.6120 0.6135 0.6180 30
A A V V V nA %/V %/V %/mA
VFB=0V, VIN=4.2V TA = +25C
Regulated Feedback Voltage
TA= 0C TA 85C TA= -40C TA 85C
VFB Input Bias Current Reference Voltage Line Regulation Output Voltage Line Regulation Output Voltage Load Regulation
VFB = 0.65V VIN = 2.5V to 5.5V, 0.01 0.04 0.0015
0.4 0.40
VIN = 2.5V to 5.5V,IOUT=10mA IOUT from 10 to 600mA
Peak Inductor Current Oscillator Frequency RDS(ON) of P-CH MOSFET RDS(ON) of N-CH MOSFET SW Leakage RUN Threshold RUN Leakage Current Thermal Shutdown Trip Threshold Output over voltage lockout
VIN=3V, VFB=0.5V or VOUT=90% Duty Cycle <35% VFB=0.6V or VOUT=100% ISW = 300mA ISW = -300mA VRUN = 0V, VSW= 0V or 5V, VIN = 5V -40C TA 85C
0.75 1.2
1.00 1.5 0.4 0.35 0.01
1.25 1.8 0.50 0.45 1 1.5 1
A MHz A V A mV
0.3
0.45 0.1 150
VOVL = VOVL - VFB
60
Note 4: 100% production test at +25C. Specifications over the temperature range are guaranteed by design and characterization.
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 5
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator FUNCTIONAL DESCRIPTION
Operation
CM3706A is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC Converter supplies 600mA output current at VIN = 3V with input voltage range from 2.5V to 6.5V.
Idle Mode Operation
At very light loads, the CM3706A automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. The PWM control loop will
Current Mode PWM Control
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current error voltage. is above the The current comparator, ICOMP, limitsthe peak
Maximum Load Current The CM3706A will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases.
Note 5: The duty cycle D of a step-down converter is defined as:
inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present.
D = TON x f OSC x 100%
frequency (1.5Mhz).
V OUT x 100% VIN
where TON is the main switch on time, and fOSC is the oscillator
Dropout Operation
When the input voltage decreases toward the value of the output voltage, the CM3706A allows the main switch to remain on for more than one switching cycle and increases the duty cycle (Note 5) until it reaches 100%. The output voltage then is the input voltageminus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. maximum junction temperature of the IC. Caution must be exercised to ensure the heat dissipated not to exceed the
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 6
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator Typical Performance Characteristics
(Test Figure 1 above unless otherwise specified)
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 7
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator
Output Voltage vs Temperature
Pulse Skipping Mode Operation
Discontinuous Operation
Start-Up from shutdown
Load step
Load step
Load step
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 8
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator APPLICATIONS INFORMATION
Setting the Output Voltage
Figure 2 above shows the basic application circuit with CM3706A adjustable output version. The external resistor sets the output voltage according to the following equation:
IN 2.5VT O 5.5V
C in 4.7uF
L 1
4 3
2.2uH
1
S W C 3706A M F R N G D VB U N
2
V IN
OT U
1%634k
5
C out 10uF 22P F
R 2
R2 VOUT = 0.6V 1 + R1
R1=316K ; R2= 316K ; VOUT =1.2V R1=316K ; R2= 470K ; VOUT =1.5V R1=316K ; R2= 630K ; VOUT =1.8V R1=316K ; R2= 1M ; VOUT =2.5V R1=316K ; R2= 1.42M ; VOUT =3.3V.
R 1
316K
C 1
1%
C 3
C 2
Figure2 Application Circuit with adjustable output versions For output voltages above 2.0V, when light-load efficiency is
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 4.7F ceramic capacitor for most applications is sufficient.
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, or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (600mA+105mA).
Output Capacitor Selection Inductor Selection
For most designs, the CM3706A operates with inductors of 1H to 4.7H. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current.The output ripple VOUT is determined by:
L=
Where
VOUT x (V IN - VOUT ) V IN x I L x f OSC
I L
VOUT
is inductor Ripple Current. Large value
VOUT x (V IN - VOUT ) 1 x ESR + V IN x f OSC x L 8 x f osc x C 3
inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 600mA, or
Input Zener Selection
In USB device application, we will add zener. The zener can be reduced the surge voltage when device plug in and plug out. Application circuit is show in Figure3.
I L =210mA.
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 9
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator PACKAGE DIMENSION
D
5 4
b1 c1
With Plating
A
c
A1 A2
E1
b
Base Metal
Section B-B
E
b b1 c c1 D E
1
e
2
3
E1
e1
b
L L1 e e1
1
1 2
A2
A
2
A1
See Section B-B
Note5: Package outline exclusive of mold flash and metal burr.
2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
L L1
Page 10
CM3706A
1.5MHz, 600mA Synchronous Step-Down Regulator
IMPORTNT NOTICE
Champion Microelectronic Corporation (CMC) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. CMC integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of CMC products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards.
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2008/03/07 Rev. 1.0
Champion Microelectronic Corporation
Page 11

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