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Synchronous Buck Converter with Integrated Power Devices
POWER MANAGEMENT Description
The SC192 is a synchronous step-down converter with integrated power devices designed for battery operated systems. The internal power switches reduce system size and cost. In addition, an efficiency of 95% can be achieved for significant line and load ranges. The SC192 is designed for single-cell Li-Ion battery applications, but also performs well in fixed 3.3V or 5V input circuits. The SC192 has a flexible clocking scheme. It can be synchronized to an external oscillator, fixed to the internal oscillator, or allowed to modulate the frequency during light loads (PSAVE) for maximum battery life, by the method called pulse frequency modulation (PFM). Shutdown places the switches in a high impedance state and turns off all control circuitry to achieve a typical quiescent current of 0.1A. Line and load regulation is to +/-0.5% of the output voltage. The internal MOSFET switches provide >1A peak current to provide a DC output of at least 700mA. Grounding the ILIM pin reduces the current limit by half. The SC192 can achieve 100% duty cycle for excellent low dropout performance and comes in a tiny MLPD-10, 3 x 3 package having a maximum height of 1mm.
SC192
Features
2.7V to 7V Input Range Output Adjustable from 0.75V to Vin Fixed Frequency or PSAVE for Maximum Efficiency Over Wide Load Current Range 700mA Guaranteed Output Current No Schottky Diode Required 35A Quiescent Current 100% Duty Cycle in Dropout 95% Efficiency Fast Transient Response Over Temperature Protection Space-saving Micro Lead-Frame Package MLPD-10 3x3
Applications
Cell Phones Cordless Phones Notebook and Subnotebook Computers PDAs and Mobile Communicators 1 Li-Ion or 3 NiMH/NiCd Powered Devices
Typical Application Circuit
SC192 Vin = 2.7V to 7V
L1
1 VIN LX 9
Vout = 0.75V to Vin
C1
8
EN ADJ 5
C5
R1 C6 R2
6
ILIM
PGND 2
10
BP
SYNC/PWM
7
C3
3 GND COMP 4
R8
C4
Revision 8, March 26, 2007
1
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SC192
POWER MANAGEMENT Absolute Maximum Ratings
Parameter V IN i n p u t SYN C/PWM Input E N In p u t PGN D to GN D LX Voltage ILIM Voltage ADJ Voltage COMP Voltage BP Voltage Thermal Impedance Junction to Ambient Output Shor t Circuit to GN D LX Current Peak IR Reflow Temperature SC192IMLTR (Soldering) 10s - 30s SC192IMLTRT (Soldering) 20s - 40s Storage Temperature Symbol V IN VSYNC V EN VPGDN V LX V IL IM VADJ VCOMP V BP JA tSC IL X T LE A D TS Maximum -0. to 7.5 -0.33 to 7 -0. to 7.5 -0.33 to 7 -0. to 7.5 -0.33 to 7 -0.3 to 0.3 -1 to VIN +1 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 VIN - 0.3 to VIN + 0.3 *57 Continuous +1.6 240 260 -65 to +160
PRELIMINARY
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied.
Units V V V V V V V V V C/W s A
C C
* Tied to PCB with 1 square inch, 2 ounce copper. Note: This device is ESD sensitive. Use of ESD handling precautions is required.
Electrical Characteristics
Unless otherwise noted: VIN = 3.6V, SYNC/PWM = VIN, ILIM = VIN, EN = VIN, TA =-40 to 85C. Typical values are at TA = +25C.
Parameter Input Voltage Range ADJ Regulation Voltage ADJ Input Current Output Voltage Adjust Range Line Regulation Load Regulation(1) P-Channel On Resistance N-Channel On Resistance
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Symbol VIN V AD J IADJ VOUT REGLINE REGLOAD RDSP RDSN
Conditions
Min 2.7 0.731
Typ
Max 57 .5
Units V V nA V % %
0.75 0
0.769 50 VIN +0.5 0.6
ADJ = 0.75V
-50 V AD J -0.5
Peak Inductor Current = 0 to 700mA ILX = 200mA ILX = 200mA
2
0 0.3 0.4
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SC192
POWER MANAGEMENT Electrical Characteristics Cont.
Unless otherwise noted: VIN = 3.6V, SYNC/PWM = VIN, ILIM = VIN, EN = VIN, TA =-40 to 85C. Typical values are at TA = +25C.
Parameter P-Channel Current Limit
Symbol I L IM ( P )
Conditions ILIM = GN D I L I M = V IN
Min 420 840 45 -320
Typ 600 1200 105 -420 35
Ma x 780 1560 165 -520 50 1 1
Units mA mA mA mA A A A A
N -Channel Current Limit Quiescent current Shutdown Current LX leakage Current PMOS LX leakage Current N MOS Oscillator Frequency SYN C Frequency Range Duty Cycle Range UVLO Threshold UVLO Hysteresis Thermal Shutdown Logic Input High Logic Input Low Logic Input Current High Logic Input Current Low
I L IM ( N )
SYN C/PWM = GN D, PSAVE Mode
IQ ISD ILXP ILXN fOSC fSYNC D V UV L VUVLHYS
SYN C/PWM = GN D, PSAVE Mode EN = 0, LX = Open, TA = 25C VIN = 5.5V, LX = 0V, EN = 0V VIN = 5.5V, LX = 5.5V, EN = 0V -20 650 500 SYN C/PWM = GN D, PSAVE Mode 20 2.35
750
830 1000 100
kHz kHz % V mV
2.5 50 160
2.65
C
V IH V IL I IH I IL
EN , SYN C/PWM, ILIM EN , SYN C/PWM, ILIM EN , SYN C/PWM, ILIM EN , SYN C/PWM, ILIM
2 0.8 -2 -2 2 2
V V A A
Notes: (1) Load regulation limits are specified from 0 to 700mA. This specification is calculated based on parameters measured individually and is not a tested parameter. See the load regulation limit graph on page 13 for more detailed view of performance.
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SC192
POWER MANAGEMENT Pin Configuration PRELIMINARY Ordering Information
DEVICE(1) SC192IMLTR PACKAGE MLPD-10 3x3 Evaluation Board
TOP VIEW
VIN BP GND COMP ADJ 1 2 3 4 5 10 PGND 9 LX 8 EN
SC192IMLTRT(2) SC192EVB
T
7 SYNC/PWM 6 ILIM
Note: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant.
MLPD-10: 3X3 10 LEAD
Pin Descriptions
Pin # 1 2 Pin Name V IN BP Pin Function Input power supply voltage; this input goes directly to the internal MOSFET switches. Bypass capacitor pin; an external capacitor combined with an internal resistor provides a filtered supply voltage for the internal control circuitry. Connect a 0.1uF capacitor from BP to ground. Analog ground. Compensation pin for the error amplifier. Output adjust pin; connect to a resistor divider to set the output voltage. Digital current limit select input. Connect ILIM to GN D for 0.6A current; connect ILIM to VIN for 1.2A current limit. Oscillator synchronization input. Tie to VIN for forced PWM mode, GN D to enable power save mode, or an external clock signal for frequency synchronization. Enable digital input; a high input enables the SC192 a low disables the device and reduces quiescent current to 0.1uA. In shutdown, LX becomes high impedance. Inductor connection to the switching FETs. Power Ground. Pad for heatsinking purposes. Connect to ground plane using multiple vias. N ot connected internally.
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3 4 5 6 7 8 9 10 T
GN D COMP ADJ I L IM SYN C/PWM EN LX PGN D Thermal Pad
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SC192
POWER MANAGEMENT Block Diagram
BP
VIN
-
ILIM
V
+
Plimit amp +
SYNC/ PW M
O and slope SC generation
-
Control logic PW M comp
CO P M
+
ADJ
Error amp + +
750mV
G ND
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5
-
EN
Nlimit comp
-
Current amp
LX
PG D N
V
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SC192
POWER MANAGEMENT Description
Description The SC192 step-down, pulse-width-modulated (PWM), DC-DC converter has an adjustable output range from 0.75V to the input voltage. The device has an internal synchronous rectifier and does not require a schottky diode on the LX pin. At moderate to heavy loads, the converter operates in the PWM mode with a fixed frequency of 750kHz. At light loads the converter enters the power save mode by modulating the frequency, pulse-frequency-modulation (PFM) which achieves high efficiency under light load conditions. Normal Mode This is a standard fixed frequency current mode topology. The current feedback is through the PMOS current path and is amplified and summed with the internal slope compensation network and DC offset. The voltage feedback loop is through the resistor divider attached to the ADJ pin. The transconductance error amplifier output is the compensation (COMP) pin with the usual external compensation network attached. The PWM COMP pin closes the loop by comparing the summed current feedback and the COMP signal to determine the length of the ON time. The period is set by the on-board oscillator or external clock attached to the SYNC pin. Power Save Mode If SYNC/PWM is DC low, power save mode is used at light loads to improve efficiency. When the output current reaches a low enough level, the part goes into a voltage hysteresis mode of operation. The current level for this is set to be the current reversal protection on the NMOS device. The output voltage is then allowed to decay to a lower threshold with the part in a reduced quiescent current (PSAVE) state. After this lower threshold is reached the part is reawoken to normal operation, but with a current offset on the COMP pin to drive the output voltage regulation point to be above an upper threshold point. However the offset is removed once the upper threshold is reached. If the load current is now sufficiently large the part will return to normal regulation, if not another PSAVE cycle will start. Frequency Foldback When the ADJ pin is low the output switching frequency is folded back in several discrete steps to protect against a short to GND on the output and improve inrush current control during start-up.
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PRELIMINARY
Forced PWM If SYNC/PWM is DC high, the forced PWM mode is enabled. This ensures that the switching frequency of the converter is maintained over the full range of output loads. This means that the current reversal threshold of the NMOS is changed to a negative value and the 100% duty cycle and power save modes are also disabled. 100% Duty-Cycle Operation Normally the control loop constrains the duty cycle of the converter with minimum on and off times, but if the output voltage droops to the lower power-save threshold and the ON time is not terminated by the PWM comparator or PMOS current limit, then the next PMOS on time is allowed to extend until either the PWM comparator or PMOS current limit trips. This is then followed by a minimum off time. This maximum on time/minimum off time is allowed to continue until the upper power-save threshold is reached. This allows the part to go into a dropout mode of operation if the input supply collapses down to the output voltage. If this happens, the output voltage is equal to the input voltage minus the voltage drop across the P-channel MOSFET. Soft Start The soft start mode is enabled after every shutdown cycle to limit inrush current from the battery. In conjunction with the frequency foldback this controls the maximum current during start-up. The PMOS current limit is stepped from 25%, to 50%, to 75%, and then 100% by an internal 2ms timer. As soon as the part reaches regulation, soft start mode is disabled.
SC192
POWER MANAGEMENT Evaluation Board Schematic
VIN
TP7 EN
R6 1k
R7 1k
R5 100k
6 5 4 TP8 ILIM TP1 VIN 1 2 3 TP4 LX 10 9 8 7 6 EN SW1 DIP
U1
VIN TP3 COMP 1 2 3 4 5 C1 10uF C3 0.1uF C4 470pF VIN BP GND PGND LX EN
TP5 VOUT
L1 10uH
C5 47pF R1 442k 1.8V
COMP SY NC ADJ ILIM
SC192
R2 309k C2 0.1uF C6 22uF TP6 SYNC
R8 28k TP2 GND
R3 100k R4 100k
SY NC
GND
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SC192
POWER MANAGEMENT Evaluation Board Gerber Plots TOP COPPER BOTTOM COPPER PRELIMINARY
TOP SILKSCREEN
BOTTOM SILKSCREEN
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SC192
POWER MANAGEMENT Applications Information
Selecting Components When selecting components for the an SC192 application the main factors are typically performance, size and cost. For higher performance the designer will select higher values of input and output capacitors to reduce ripple current and voltage. However, for an application that can tolerate higher ripple, less expensive and smaller components can be utilized. The schematics below show two possibilities. The first shows the use of 10F capacitors on the input and output with L1 = 10H, while the second shows the use of smaller less expensive 4.7F capacitors and L1 = 4.7H. The only circuit consideration for choosing one over the other is the compensation components C4 & R8. When these components are in place the values of R2 can be chosen for a given output voltage. The values that should be used are indicated in Table 1 below. Using a different value for R1 is not advised since this will change the loop characteristics and may cause the supply to become unstable. Any output voltage is achievable using R1 of 442k and then selecting R2 to achieve the desired output voltage. The equation for VOUT is:
R1 Vout = + 1 * 0.75 R2
Because the SC192 has external compensation the use of small inexpensive ceramic capacitors can be used for the output capacitor allowing the designer greater flexibility.
VIN
1 2 3 4 5 C1 10uF C3 0.1uF C4 470pF R8 12k
VIN BP GND
PGND LX EN
10 L1 9 10uH 8 7 6 C6 10uF R2 C5 47pF R1 442k VOUT
COMP SY NC ADJ ILIM
SC192
VIN
1 2 3 4 5 C1 4.7uF C3 0.1uF C4 470pF R8 6.19k
VIN BP GND
PGND LX EN
10 L1 9 4.7uH 8 7 6 C6 4.7uF R2 C5 47pF R1 442k VOUT
COMP SY NC ADJ ILIM
SC192
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SC192
POWER MANAGEMENT Applications Information Cont.
TABLE 1
VOUT 3.3V 2.5V 1.8V 1.5V 1.0V R2 R2 130k 187k 309k 442k 1.30M C4 = 470pF R8 = 12k C4 = 470pF R8 = 28k C4 = 470pF R8 = 6.19k C6 = Cout = 10uF L1 = 10uH C6 = Cout = 22uF L1 = 10uH C6 = Cout = 4.7uF L1 = 4.7uH
PRELIMINARY
The plots below were taken at Vin = 3.6V, Vout = 1.8V, with the compensation components listed in Table 1. The upper plot is LX, the middle plot is output voltage, the lower plot is the current transient of 0.1A to 0.6A PSAVE, Cout = 20uF, Lout = 10uH PWM, Cout = 20uF, Lout = 10uH
PSAVE, Cout = 10uF, Lout = 10uH
PWM, Cout = 10uF, Lout = 10uH
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SC192
POWER MANAGEMENT Applications Information Cont.
PSAVE, Cout = 4.7uF, Lout = 4.7uH PWM, Cout = 4.7uF, Lout = 4.7uH
Inductor Selection The inductor values listed in Table 1 will work for nearly all combinations of output current and output voltages. After selecting 4.7uH or 10uH for the inductor value two additional inductor parameters should be considered. The current rating of the inductor and the DC resistance. The DC resistance has a great impact on efficiency due to copper losses. However, small inductors tend to have higher DC resistance. Therefore a compromise between size and efficiency will need to be made. The inductor current must be chosen to prevent the inductor from saturation. The most conservative approach would be to select an inductor with a saturation current slightly above the maximum current capability of the SC192 which is 1.56A peak current for ILIM = Vin or 780mA for ILIM = GND. A more accurate design of the inductor would be to rate the inductor for the maximum output current plus the inductor ripple current that can be calculated as follows:
f = Switching frequency L = Inductor Value IL= Peak-to-peak inductor ripple current IL = Maximum inductor current VOUT = Output voltage VIN = Input voltage COUT = Output Capacitance IOUT = Output Current IOUT(MAX) = Maximum DC Output Current Output Capacitor Selection Because the SC192 has external compensation available, low ESR ceramic capacitors can be used. This eliminates the need for bulky tantalum capacitors. Values for the output capacitors in Table 1 will work for nearly all combinations of output current and output voltages. The equation for determining the size of the output capacitor in terms of minimizing the ripple voltage is given as follows:
IL(MAX) = IO(MAX ) +
IL 2
1 VO = IL * + ESR 8 * COUT * f
Input Capacitor Selection The input ripple current can be reduced with properly selecting the input capacitor. Again, values for the input capacitors in Table 1 will work for nearly all combinations of input current and output voltages. The input capacitor should be rated for the maximum input ripple current calculated as:
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VOUT 1 IL = VIN * VOUT L* f
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SC192
POWER MANAGEMENT Applications Information Cont.
IRMS = VOUT * VIN - VOUT * IOUT VIN
0.45 0.40 Load Regulation (%) 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 1 20 40 60 80 100 200 300 400 500 600 Ouput Current (mA) Vo = 1.8V Vo = 2.5V
PRELIMINARY
Load Regulation at Vin = 3.6V
The worst case RMS ripple current occurs at a duty cycle of 0.5 and its value at that point is
IOUT . 2
Ceramic capacitors are recommended for input capacitors because of their low ESR and high ripple current capabilities. In addition, it is advised that the input capacitor be placed as close to the input pin of the IC as possible. Layout Considerations PCB layout is of utmost importance because the switching frequency is 750kHz with peak currents over 1A. A careful layout will avoid potential stability and EMI problems. Traces should be as wide and as short as possible. Keep the input capacitor as close to the package as possible. This will help minimize large loop areas. Keep the power ground and analog ground separated and tie the two together at one common point. Notice the top copper Gerber plot (see Page 8), pin 3 and pin 10 are tied together under the package. Be aware of the high current paths and avoid tying signal grounds to the high power grounds where the signal paths might experience large fluctuations in voltages as high currents pass though copper traces.
Efficiency at Vin = 5V
100 95 90 85 80 75 70 65 60 1 10 30 50 70 90 200 400 600 Load Current (mA) Vo = 3.3V
Efficiency (%)
Efficiency at Vin = 3.6V
100 Efficiency (%) 95 90 85 80 1 10 30 50 70 90 200 400 600 Load Current (mA) Vo = 2.5V Vo = 1.8V
Line Regulation At Iout = 300mA
0.10 Line Regulation (%) 0.08 0.06 Vo = 1.8V 0.04 0.02 0.00 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8
Input Voltage (Volts)
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SC192
POWER MANAGEMENT
Line Regulation at IOUT = 300mA
0.14
1.0 0.9
SC192 Load Regulation Limits
Line Regulation (%)
Load Regulation (%)
0.12 0.10 0.08 Vo = 2.5V 0.06 0.04 0.02 0.00 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 0.2 0.4 0.6 0.8 1 1.2
Load Reg Max Load Reg Typ Load Reg Min
Input Voltage (Volts)
Peak Inductor Current (Amps)
Oscillator Frequency vs Temperature Over VIN
760 755 750
Vin = 2.7 V Vin = 3.6V Vin = 5.5V
Oscillator Frequency vs VIN Over Temperature
760 755 750
Fosc (kHz)
745 740 735 730 725 720 715 710 -60 -40 -20 0 20 40 60 80
Fosc (kHz)
745 740 735 730 725 720 715 710
Temp = -40C Temp = 0C Temp = 25C Temp = 85C Temp = 125C
100
120
140
2
2.5
3
3.5
4
4.5
5
5.5
6
Temp (OC)
Vin (Volts)
Shutdown Current vs Temperature
0.9
Shutdown Current (A)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 0 25 85
O
Vin = 3.6V
125
Temperature ( C)
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SC192
POWER MANAGEMENT Outline Drawing - MLPD-10, 3 x 3
A E
PRELIMINARY
B
DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX
A A1 A2 b C D E e L N aaa bbb .031 .039 .000 .002 (.008) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 0.80 1.00 0.00 0.05 (0.20) 0.18 0.23 0.30 1.87 2.02 2.12 1.06 1.21 1.31 2.90 3.00 3.10 0.50 BSC 0.30 0.40 0.50 10 0.08 0.10
E PIN 1 INDICATOR (LASER MARK)
A aaa C A1 C 1 LxN 2 A2 C SEATING PLANE
D
N e bxN bbb CAB
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS.
Marking Information
Top Marking
192 yyww
yy = two-digit year of manufacture ww = two-digit week of manufacture
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SC192
POWER MANAGEMENT Land Pattern - MLPD-10, 3 x 3
K
DIM
H C G H K P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.112) .075 .055 .087 .020 .012 .037 .150 (2.85) 1.90 1.40 2.20 0.50 0.30 0.95 3.80
(C)
G
Z
Y X P
NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
Visit us at: www.semtech.com
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