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Si9177
New Product
Vishay Siliconix
200-mA PSM Step Down Converter with Bypass Capability
FEATURES
D D D D D D D D D D D 2.7-V to 6-V Input Voltage Range 1.2-V to 5-V Output Efficiency of 95% for VOUT of 3.3 V @ 200-mA Load Selectable Pulse Skipping Modulation (PSM) or Bypass Mode (BP) Operation 150-mW Bypass Switch for 800-mA Loads Integrated MOSFET with Low External Part Count Shutdown Current <1 mA Integrated UVLO and Power on Reset Integrated Soft-Start Over Temperature Protection MLP33-10 or MSOP-10 Packages
APPLICATIONS
D D D D D Cellular Phones, Cordless Phones Computer Point of Use, Notebook PDAs Battery Powered Devices MP3 Players
DESCRIPTION
The Si9177 is a dual-mode power adjustable output converter. When it is set to PSM mode, the Si9177 operates as a pulse-skipping-modulation controlled step-down (buck) converter with an output voltage range of 1.2 V to 5 V. It has an integrated MOSFET, capable of supplying 200-mA load current with a 1.5-mH inductor. The output voltage is adjusted by a resistive divider on the FB pin. The typical conversion efficiency is above 90%. A logic HIGH at the BP/PSM pin puts Si9177 in bypass mode. The main PMOS buck switch is forced to turn on at 100% duty cycle, overriding the FB signal. The voltage differential between input and output is the resistive voltage drop on the internal 150-mW PMOS and the inductor. The Si9177 delivers 800-mA load in bypass mode. The Si9177 is available in the space saving MLP33-10 and MSOP-10 packages. In order to satisfy the stringent ambient temperature requirements, the Si9177 is rated to handle the industrial temperature range of -25_C to 85_C.
TYPICAL APPLICATION CIRCUIT
VIN CIN
1 2
VIN VIN
10 LX LX 9 1.5 mH VOUT COUT R1
SI9177
3 4 5
GND
8
ON/OFF BP/PSM
ENABLE BP/PSM NC
FB REF
7 6 CREF R2
Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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Si9177
Vishay Siliconix
New Product
ABSOLUTE MAXIMUM RATINGS (TA = 25_C)
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 V BP/PSM, ENABLE, FB, LX . . . . . . . . . . . . . . . . . . . . . . . . - 0.3 V to VIN + 0.3 V Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 55 to 150_C Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150_C Power Dissipation (Package)a. MLP33-10b. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 mW MSOP-10c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915 mW Thermal Impedance (QJA) MLP33-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135_C/W MSOP-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71_C/W Notes a. Device mounted with all leads soldered or welded to PC board. b. Derate 7.4 mW/ _C above 25_C. c. Derate 14 mW/ _C above 25_C.
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.
RECOMMENDED OPERATING RANGE
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 V to 6 V CIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 mF COUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 mF Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 mH CREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open Operating Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . - 25 to 85 _C
SPECIFICATIONS
Test Conditions Unless Specified Parameter Converter Operation
Input Voltage Maximum Bypass Mode Current Maximum PSM Mode Current MOSFET On-resistance Power Supply Rejection Feedback Voltage IOUT rDS(on) PSRR VFB IREF = 0 IREF = 0, TA = 25_C CREF = 0.1 mF, See Figure 1 See Figure 1 1.175 1.195 VIN w 3.3 V VIN 2.7 800 200 150 60 1.215 1.215 1.255 1.235 V 300 mA mW dB 6 V - 40_C to 85_C VIN = VDD , CIN = 10 mF 85_C, DD, COUT = 4.7 mF, L = 2.2 mH, 2.6 V v VIN v 5.5 V R1 = 11.3 kW, R2 = 20 kW
Limits Mina Typb Maxa Unit
Symbol
Start-Up
Start-Up Delay Time Soft Start Time tDELAY tss 5 100 ms ms
ENABLE, BP/PSM
Logic High Logic Low Input Current VIH VIL IIH IIL ENABLE, BP/PSM = VIN ENABLE, BP/PSM = GND 1 1 1.5 0.4 V mA
Protection
Under Voltage Lockout Under Voltage Lockout Hysteresis Thermal Shutdown Thermal Shutdown Hysteresis VUVLO VHUVLO TSD THSD Temperature rising VIN = 3.3 V 2.2 2.35 0.1 165 25 2.5 V _C
Supply Current
BP Mode PSM Mode Shutdown IIN VIN = 3 3 V 3.3 VIN = 3.3 V, ENABLE = 0 V 75 190 110 250 1 mA
Notes a. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum, is used in this data sheet. b. Typical values are for DESIGN AID ONLY, not guaranteed or subject to production testing. c. Guaranteed by design and characterization, not subject to production testing. www.vishay.com Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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Si9177
New Product
Vishay Siliconix
PIN CONFIGURATION
MSOP-10
VIN VIN ENABLE BP/PSM NC
1 2 3 4 5 10 9 8 7 6
LX LX GND FB REF
ORDERING INFORMATION
Part Number
Si9177BM-TI Si9177BM TI - 25_C to 85_C SI9177BH-TI Tape and Reel
Temperature Range
Package
Top View
Eval Kit
Si9177DB
Temperature Range
- 25_C to 85_C
Board Type
Surface Mount
MLP33
VIN VIN ENABLE BP/PSM NC 10 9 8 7 6 LX LX GND FB REF
2 3 4 5
Top View
PIN DESCRIPTION
Pin No.
1, 2 3 4 5 6 7 8 9, 10
Name
VIN ENABLE BP/PSM NC REF FB GND LX
Function
Input voltage source for buck converter, MOSFET driver, and IC control circuits. Logic high enables the converter. Logic low shuts down the IC and decreases current consumed to <1 mA. Logic high = Bypass mode, logic low = PSM mode. No Connection 1.215-V reference. Direct output voltage sense feedback IC ground
Inductor connection node
TIMING WAVEFORMS
90%
VOUT 10%
VIN
tDELAY = Start-Up Delay Time tSS = Soft-Start Time
t
DELAY
t
SS
FIGURE 1. Soft-Start Timing
Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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Si9177
Vishay Siliconix
FUNCTIONAL BLOCK DIAGRAM
VIN VIN
New Product
REF BP/PSM
Reference Generator
UVLO
POR
BP
PSM ENABLE VADJ
PSM/BP Controller Driver
LX LX
Turn-On Control
Zero Current Detect +
NC FB
+ Turn off Control
-
+
Peak Current Comparater 0.6 A
GND
APPLICATION CIRCUIT
VIN CIN 10 mF
1 2
VIN VIN
10 LX LX 9 1.5 mH VOUT COUT 10 mF R1
SI9177
3 4 5
GND
8
ON/OFF BP/PSM
ENABLE BP/PSM NC
FB REF
7 6 R2 CREF
MLP33-10
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Document Number: 70312 S-03663--Rev. B, 07-Apr-03
Si9177
New Product
DETAIL OPERATIONAL DESCRIPTION
Start-Up load. This mode is enabled by setting the BP/PSM pin to a logic HIGH. In this mode the IC ignores the feedback signal at the FB pin, forcing the internal p-channel MOSFET to turn on continuously. The input-to-output voltage differential is reduced to the voltage drop across the 150-m MOSFET and the inductor. Si9177 can bypass 800 mA at 95% typical efficiency or provide nearly the entire input voltage to the load. Whenever the converter enters BYPASS mode, the p-channel MOSFET turns on gradually within 40 s to reduce surge current to the input capacitor. Shutdown Si9177 is designed to conserve as much battery life as possible by decreasing current consumption during normal operation, as well as the shutdown mode. With logic LOW level on the ENABLE pin, the current consumption of the IC is decreases to less than 1 A by shutting off all circuits. A logic HIGH enables the controller, allowing start up as described in the "Start-Up" section above. Reference and Power-On-Reset Timer The reference voltage of Si9177 is set to 1.215 V. It is internally connected to the non-inverting input of the error amplifier. The power on reset delay time is set by the capacitance on the REF pin and can be determined from the following relationship:
tPORDELAY = 4 104 CREF
Vishay Siliconix
When voltage is first applied to the VIN pin, the UVLO circuitry prevents the internal p-channel MOSFET from turning on. Once the VIN voltage exceeds the UVLO threshold of 2.4 V, and with no other shutdown condition detected, an internal power-on-reset timer is activated to delay the start of switching if the BP/PSM pin is held a logic LOW level. The amount of delay is set by the capacitor CREF on the REF pin and the peak current in the inductor is limited to 600 mA. If the BP/PSM pin has a logic HIGH applied, then Bypass Mode soft-start is achieved by gradually turning on the p-channel MOSFET in 40 s insuring that the output voltage rises smoothly. Pulse Skipping Mode
Si9177 is designed to operate with light loads. When the BP/PSM pin is connected to logic LOW level, the Si9177 operates in pulse-skipping mode. PSM enhances efficiency in light load conditions when compared to fixed frequency PWM mode because switch conduction losses, gate charge and switching losses are reduced. By delivering energy to the load only when needed, the p-channel MOSFET gate capacitance is charged and discharged less frequently and MOSFET conduction loss is minimized thereby reducing total losses and increasing converter efficiency. In PSM, the switching frequency, fSW, increases as and decreases as the load current increases and decreases. The typical conversion efficiency in PSM mode is 90%.
By operating as a constant on-time converter, the Si9177 achieves PSM operation. The p-channel MOSFET switching transistor is turned on to deliver energy to the load. The switch remains on for the minimum on-time or until the inductor current reaches 600 mA. If the applied on-time is sufficient to increase the output voltage above the in-regulation set point (FB pin voltage is greater than VFB), the p-channel MOSFET turns off for a minimum off-time and continues to apply constant on-time pulses to insure regulation is maintained. If the on-time of the p-channel switch causes the output voltage to rise above the set point, the converter turns off and remains off until the voltage on FB decreases below VFB. The on-time and minimum off-time are set internally to minimize ripple voltage at the maximum load current. The Si9177 has internal compensation reducing the number of required components and is designed for an inductor value of 1.5 H and an output capacitor value of 10 F. BYPASS Mode
Output Voltage The Si9177 is designed with an adjustable output voltage, VOUT, which is set by resistors R1 and R2, and the feedback voltage, VFB. VOUT is defined according to the following relationship:
VOUT + 1 ) R1 R2
VFB
where VFB is 1.215 V. The values of R1 and R2 should be kept between 5 k and 100 k. Power Switches The p-channel MOSFET switch is integrated in Si9177 for optimum performance and minimum overall converter size. This MOSFET is designed to minimize the gate charge loss as well as the conduction loss. The typical on-resistance is 150 m with a minimum input voltage of 3.3 V.
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Si9177 can also operate in BYPASS mode to handle heavy load currents or to provide the maximum output voltage to the
Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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Si9177
Vishay Siliconix
New Product
DETAIL OPERATIONAL DESCRIPTION (CONT'D)
An external Schottky diode is required for PSM mode operation. The Schottky diode handles the freewheeling inductor current after the p-channel MOSFET is turned off. The current rating of the Schottky is based on the maximum load current in PSM mode with the conduction time being the greatest at maximum input voltage. Combined with the maximum load current of 200 mA, the Schottky must be able to conduct 200 mA continuously. Since the forward voltage drop of the diode, VF, determines the conduction losses, select the diode with the lowest VF to maximize the converter's efficiency. The diode should also be selected for fast switching speed to improve efficiency. The diode must be connected from the LX pin to GND. Over Temperature Protection Si9177 includes an over temperature protection circuit to prevent thermal runaway in the MOSFET switch. If the junction temperature reaches 165_C, an internal soft-start capacitor is discharged, shutting down the output stage. The converter remains disabled until the junction temperature falls below 140_C, allowing the converter to resume operation.
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
Supply Current vs. Input Voltage
180 240 220 PSM Mode Current (mA) 200 rDS (mW) 140 180 160 140
rDS(on) vs. Input Voltage
160
85 _C
120
25 _C
100
- 25 _C 80 120 BP Mode 100 60 2 3 4 5 6 7 Voltage (V) 2 Voltage (V) 3 4 5 6 7
Efficiency vs. Load Current
100.00 VIN = 3.6 V 95.00 VOUT = 3.0 V Frequency (kHz) 500 450 400 350 300 250 200 150 100 50 70.00 0 50 100 150 200 250 0 0
Switching Frequency vs. Load Current
VOUT = 3.3 V
Efficiency (%)
90.00 VOUT = 2.2 V 85.00
VIN = 4.0 V
80.00
75.00
VIN = 6.0 V
50
100 Current (mA)
150
200
Current (mA)
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Document Number: 70312 S-03663--Rev. B, 07-Apr-03
Si9177
New Product
TYPICAL WAVEFORMS
Typical Switching Waveforms VIN = 4 V, VOUT = 2.0 V, IOUT = 6 mA
VOUT 50 mV/div AC Coupled
Vishay Siliconix
Typical Switching Waveforms VIN = 4 V, VOUT = 2.0 V, IOUT = 100 mA
VOUT 50 mV/div AC Coupled
VLX 2 V/div
VLX 2 V/div
ILX 200 mA/div 2 ms/div.
ILX 200 mA/div
5 ms/div.
Typical Switching Waveforms VIN = 4 V, VOUT = 2.0 V, IOUT = 200 mA
VOUT 50 mV/div AC Coupled
Load Transient VIN = 4 V, VOUT = 2.0 V
VOUT 100 mV/div AC Coupled
VLX 2 V/div
ILX 200 mA/div 0.5 ms/div. 100 ms/div.
IOUT 100 mA/div
Start-Up VIN = 4 V, VOUT = 2.0 V, IOUT = 100 mA VENABLE = VIN
Start-Up from Disable VIN = 4 V, VOUT = 2.0 V, IOUT = 100 mA
VIN 2 V/div
VENABLE 2 V/div
VOUT 1 V/div 50 ms/div. 50 ms/div.
VOUT 1 V/div
Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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Si9177
Vishay Siliconix
TYPICAL WAVEFORMS
New Product
Start-Up in Bypass Mode VIN = 4 V, IOUT = 100 mA VENABLE, BP = VIN
VIN 2 V/div
VOUT 2 V/div 50 ms/div.
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Document Number: 70312 S-03663--Rev. B, 07-Apr-03
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