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Push-Pull Controller .or Isolated Power Supplies
POWER MANAGEMENT Description
The SC4820 is a controller with maximum features for its small SO-8 outline. It is optimized for cost critical applications requiring minimum space. The controller is intended for converters used in pushpull and bridge topologies, typically in point of use power supplies with 18V to 75V supply rails, but can be readily adapted for other input voltage ranges. The controller is a current mode device, with slope compensation, and cycle by cycle current limit, which provides rapid transient response and prevents core saturation. Use of low voltage, fully differential logic in the control circuit, allows high frequency capability together with optimum low noise performance. The device is capable of driving power MOS.ETs with up to 1 Amp peak drive current, and is available in two switching frequency options.
SC4820
PRELIMINARY .eatures
K Current mode K Cycle by Cycle current limit K Direct drive for N-channel MOS.ETs with nonK Internal leading edge blanking K Undervoltage lockout with user K K K K K
programmable hysteresis Soft start Dead time control built in 1 Amp peak drive capability Precise thermal shutdown Trimmed switching frequency overlap protection
Applications
K Telecom and datacom power supplies K Point of use power supplies
Typical Application Circuit
Revision 2, .ebruary 2001
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POWER MANAGEMENT Absolute Maximum Ratings
Parameter V CC Cload Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 seconds J C J A TA TSTG TLEAD
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
Units V nF C/W C/W C C C Symbol Maximum 18 5 40 165 -40 to 85 -60 to 150 300
SC4820
Electrical Characteristics
Unless specified: VCC = 12V; TA = 25oC
Parameter Supply Voltage Range VCC Lockout Threshold Supply Current Supply Current Supply Current Undervoltage Lockout Lower Threshold Hysteresis Current (1) Soft Start Charge Voltage Input Resistance Discharge Voltage
(2)(3) (2)(3)
C o n d it io n s
M IN 9 6.5
T YP 7 7 22 33
MAX 17 8 10 30 38
U N IT S V V mA mA mA
No gate pulses FOSC = 250 kHz, CL = 3nF FOSC = 500 kHz, CL = 3nF
5 18 30
3.182 (-5%) 39 3 50 ISS (inj) = 100A ISS (inj) = 3mA 2.25 SC4820A, Tj = 25C SC4820B, Tj = 25C Internally Preset Modulation sensitivity CL = 3nF 0.8 1.6
2
3.350 43 3.1 60 100 0.5 2.55 250 500 25 50 0.5 150 1.05 1.9
3.518 (+5%) 47 3.25 70 200 0.6 2.75 262.5 (+5%) 525 (+5%)
V A V kohm mV V V kHz kHz % mVp-p %/A ns
Peak Discharge Voltage Oscillator
SS / Drive Enable Threshold Operating Frequency (when trimmed to 250kHz) (when trimmed to 500 kHz) Slope Compensation (Preset) (5) Slope Compensation (External) Current Sense Propagation Delay to Gate Current Limit Threshold Crowbar Threshold
2001 Semtech Corp.
(4)
237.5 (-5%) 475 (-5%)
1.4 2.2
V V
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POWER MANAGEMENT Electrical Characteristics (Cont.)
Parameter F eed b ack Input Quiescent Voltage Input Resistance
(5) (5)
Push-Pull Controller .or Isolated Power Supplies
C o n d it io n s M IN T YP MAX U N IT S
SC4820
PRELIMINARY
4.5 In linear range 100
5.0
5.5
V Kohm
Gain (to comp. Input) Drive Gate "Low" Voltage Gate "Low" Voltage Gate "High" Voltage Peak Sink Current Peak Source Current Rise Time Fall Time
(5)
1
VCC = open, 2A into G1, G2 VCC = 12V, no switching, 1mA into G1, G2 VCC - 1.2 0.7 0.7 CL = 3nF CL = 3nF VCC - 1.0 1 1 60 60
0.1 1
V V V A A ns ns
Leading Edge Blanking Blank Time
(5)
50
ns
Dead Time Control Dead Time F = 250kHz F = 500kHz Thermal Protection High Threshold Hysteresis 150 10 C C 350 250 ns ns
Notes: (1) When input voltage is ramped up, 43A flows into UVLO pin until pin voltage reaches "HIGH" threshold. (2) Clmax = 20nF @ 250kHz; Clmax = 15nF @ 500kHz. (3) Specified current, lss (inj) flows into soft start pin, soft start voltage is "Low". (4) 10A injected or removed from soft start pin will change slope compensation to 30% and 20%, respectively. (5) Guaranteed by design.
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POWER MANAGEMENT Pin Configurations
(TOP VIEW)
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
Temp. Range (TJ) -40 to 150C
SC4820
Ordering Information
Device(1) SC4820AISTR SC4820BISTR SC4820EVB-A SC4820EVB-B Freq. kHz 250 500 SO-8 Device
SC4820A Evaluation Board SC4820B Evaluation Board
Note: (1) Only available in tape and reel packaging. A reel contains 2500 devices.
(8-Pin SOIC)
Pin Descriptions
Pin# 1 2 3 Pin Name VC C GA UVL Chip power supply voltage. Gate drive of FET A. Under voltage lockout. This pin acts as a 43A current sink below UVLO upper threshold when the UVLO sense voltage is swept upwards from zero volts. The hysteresis is determined by this sink current and the source resistance of the UVLO sense voltage divider resistors, as observed at the UVLO. Feedback. This pin has a high source resistance in the linear region and below. Source resistance reduces to 3 kohm above the linear region. Current sense. The pin receives the current sense signal from the current transformer. The current limit threshold is typically 1.05V. The Crowbar Threshold is at 1.9V typical. When the Crowbar Threshold is reached the Gate Drives are turned off and latched "Low". The soft start pin is also latched to approx. 1.0V. This condition stays unchanged until the soft start pin is momentarily forced to GND, or the supply voltage is switched off. Soft start/Enable. The input resistance to this pin is 60 kohm typical. The input resistance and the external soft start capacitor determine the soft start delay. Soft start begins as the Drive Enable threshold is passed. After the soft start cycle is completed, the soft start pin voltage is 3.1V. When up to 10A is injected into this pin, the internal ramp compensation changes from its preset value which is 25% to approx. 30% or 20%, respectively. The soft start pin can also be utilized as Enable/Disable pin. When the soft start pin voltage is held below the Drive Enable threshold, the device will not generate switching waveforms. When the device is latched in "Crowbar" condition, the soft start pin is set to 1V. The "Crowbar" condition can be removed by momentarily shorting the soft start pin to GND. Gate drive of FET B. Ground. Description
4 5
FB IS
6
SS
7 8
GB GND
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POWER MANAGEMENT Block Diagram
Push-Pull Controller .or Isolated Power Supplies
SC4820
PRELIMINARY
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POWER MANAGEMENT Typical Applications
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
SC4820
ISOLATED APPLICATION - 48V Input, 5V/10A Output. Using SC4820B
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POWER MANAGEMENT Typical Applications (Cont.)
Bill of Material for Isolated Application
Ite m 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Qty 2 2 2 1 1 1 5 3 1 1 1 1 1 2 1 3 1 1 1 1 Re fe r e nce C1,C2 C3,C4 C6,C7 C8 C9 C11 C 17 - C 21 C22,C23,C24 C 33 C 35 C 36 C 37 C 47 D1,D2 D3 D4,D7, D9 D5 D8 D 10 L1
Push-Pull Controller .or Isolated Power Supplies
SC4820
PRELIMINARY
Par t Numbe r / Value 2.2n, 50V, 1206, Cer. 150p, 200V, 5%, NPO, Cer. 1.0u, 100V, 1812, Cer. 150p, 1206, Cer. 100p, 1206, Cer. 1.0u, 1206, Cer. 33u, 8V, SMD, Poly. Alum. Cap. 0.33u, 1206, Cer. 33n, 1206, Cer. 4.7n, 1206, Cer. 82n, 1206, Cer. 0.47u, 1206, Cer. 0.1u, 1206, Cer. 35V, 25A, TO-220AC, Schottky 250V, 100mA, SOT-23 30V, 200mA, Schottly 12V, 500mW, SOD-123 75V, 50mA, SOT-23 10V, 500mW, SOD-123 E-I Core - Inductor 4-Layer FR-4 PCB, Inductor, 1.5H
Manufactur ing Any Any Any Any Any Any. Panasonic P/N: EEF-CDOK330R Any Any Any Any Any Any Motorola P/N: MBR2535CTL Motorola P/N: BAS21LT1 Any. MA729-(TX) Any. MMSZ4699T1 Motorola P/N: BAS16LT1 Any. MMSZ4697T1 Magnetics. R-41805-E&I Any IR P/N: IRF640 Any. FMMT493TA Any Any Any
21 22 23 24 25
2 1 2 2 2
M1,M2 Q1 R1,R30 R2,R3 R5,R6
200V, 18A, 0.18 ohm, TO-220AB, MOSFET 100V, 1000mA, SOT-23, NPN Bipolar 2.2, 5%, 1206, 1/8W 5.1, 5%, 1206, 1/8W 56, 5%, 1206, 1/8W
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POWER MANAGEMENT Typical Applications (Cont.)
Bill of Material for Isolated Application (Cont.)
Ite m 26 27 28 29 30 31 32 33 34 35 36 37 Qty 1 1 2 1 1 1 1 1 1 1 1 1 Re fe r e nce R7 R8 R10,R28 R11 R12 R15 R21 R26 R27 R31 R33 T1
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
SC4820
Par t Numbe r / Value 40.2k, 1%, 1206, 1/8W 200, 5%, 1206, 1/8W 1.00k, 1%, 1206, 1/8W 6.04k, 1%, 1206, 1/8W 51.1k, 1%, 1206, 1/8W 10.0, 5%, 1206, 1/8W 4.99k, 1%, 1206, 1/8W 34.0k, 1%, 1206, 1/8W 11.0k, 1%, 1206, 1/8W 10k, 5%, 1206, 1/8W 33.2, 1%, 1206, 1/8W E-I Core - Main Transformer 6-Layer FR-4 PCB, Main Transformer
Manufactur ing Any Any Any Any Any Any Any Any Any Any Any Magnetics. P/N: R-41805-E&I Any Panasonic: P/N: TJ0042T Semtech P/N: SC4820B Any. MOC206-M Semtech P/N: SC4431CSK.5 Semtech P/N: SC431LCSK-.5
38 39 40 41
1 1 1 1
T2 U1 U3 U4 *
Current Sensor Transformer, 1:100 Push-Pull Controller for Isolated Power Supplies Surface Mount Optocouplers Shunt Regulator Low Voltage Adjustable Shunt Reg.
Notes: 1. * indicates optional parts. 2. Some parts are selected due to availability or lead time, and are not optimized.
2001 Semtech Corp.
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POWER MANAGEMENT Typical Applications (Cont.)
Push-Pull Controller .or Isolated Power Supplies
SC4820
PRELIMINARY
NON-ISOLATED APPLICATION - 48V Input, 3.3V/10A Output. Using SC4820A
2001 Semtech Corp.
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POWER MANAGEMENT Electrical Characteristic Curves
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
SC4820
All of the characteristic curves are: 1. .or isolated application with 36 ~ 75V input, 5V/10A output, and 500kHz switching frequency 2. Tested at 25C ambient temperature. Typical output ripple voltage at 48V input and full load
Output Volage (50 mV/div)
Time (1 us/div)
Typical start-up at 48V input and full load
Output Volage (1 V/div)
Time (5 ms/div)
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POWER MANAGEMENT Electrical Characteristic Curves (Cont.)
Push-Pull Controller .or Isolated Power Supplies
SC4820
PRELIMINARY
Typical transient response to step increase in load from 50% to 75% of full load at 0.1A/s slew rate and 48V input.
Output Voltage (100 mV/div)
Output Current (2 A/div)
Time (100 us/div)
Typical transient response to step decrease in load from 50% to 25% of full load at 0.1A/s slew rate and 48V input.
Output Voltage (100 mV/div)
Output Current (2 A/div)
Time (100 us/div)
2001 Semtech Corp.
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POWER MANAGEMENT Outline Drawing - S0-8
Push-Pull Controller .or Isolated Power Supplies
PRELIMINARY
SC4820
Land Pattern - S0-8
Contact Information
Semtech Corporation Power Management Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 .AX (805)498-3804
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