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CS3972
CS3972
1.25A High Efficiency Switching Regulator
Description
The CS3972 is a 1.25A, 60V, current mode, high efficiency, switching regulator circuit. It can be configured in buck, boost, forward, isolated and non-isolated topologies, using a single-ended switch. The IC contains a 1.25A high efficiency output switch, precision bandgap reference, voltage regulator, error amplifier, oscillator, control, and protection circuitry. Output transistor efficiency is achieved by keeping the switch in quasi-saturation when it is on. This minimizes the switch turn-off delay time and power dissipation, an important consideration for applications with wide ranging loads. The precision reference is internally trimmed to 1.24V, while the oscillator frequency is internally trimmed to 40kHz. The on board 2.3V regulator powers the internal circuitry. By keeping the voltage regulator at 2.3V, the IC is able to operate down to 3V and maintain a constant input supply current of 6mA(typ). Synchronization mode is achieved by applying a pulsating VC voltage of less than 0.2V with a duration of about 0.5s to VC pin. The switching frequency can be adjusted from 50kHz to 70kHz. The IC's synchronization mode is set externally. Protection circuitry includes a variable current limit with external voltage clamp, under-voltage and over-temperature protection.
Features
s 75VMAX, 2APEAK Internal Switch s 3V to 60V Input Voltage Range s 6mA Input Supply Current s 1.24V Precision Reference s 40kHz Switching Frequency s Variable Current Limit with External Voltage Clamp s Under-Voltage Protection s Over-Temperature Protection s External Synchronization
Package Options
Block Diagram
NC VC VFB
VSW VIN 2.3V Reg Output Protection
1
16L SO Wide
Gnd NC E2 VSW NC E1 NC VIN
NC NC NC
40kHz OSC
Logic
Driver
1.25A, 75V Switch
NC NC
+ VC
COMP Gnd 1
8L PDIP
E2 VSW E1 VIN
5L TO-220
Tab (Gnd)
VFB
Error Amp + 1.24V Ref
VC
+ Current Amp 0.22
0.22 E2 * E1 * Gnd
VFB NC
1 VC 2 VFB 3 Gnd 4 VSW 5 VIN 1
*Always connect E1 to Ground Pin on DIP package. Both emitters are tied to ground on TO-220 Package.
Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com
Rev. 6/23/99
1
A
(R)
Company
CS3972
Absolute Maximum Ratings Input Voltage Range ........................................................................................................................................................3V to 60V Output Switching Voltage.........................................................................................................................................................75V Voltage Transient (tr=10s, tf=400ms) ......................................................................................................................................60V ESD (Human Body Model; R=1.5k, C=100pF) ...................................................................................................................2kV Junction Temperature Range...............................................................................................................................-40C to +150C Storage Temperature Range ................................................................................................................................-65C to +150C Lead Temperature Soldering Wave Solder (through hole styles only)......................................................................................10 sec. max, 260C peak Reflow (SMD styles only) ......................................................................................60 sec. max above 183C, 230C peak Feedback Pin Voltage (1ms transient)...................................................................................................................................15V
Electrical Characteristics: For 3VVCC60V, -40CTA125C unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
s Reference Voltage Line Regulation Feedback Input Current Minimum Input Voltage Supply Current Supply Current Increase during switch on time Switching Frequency Maximum Duty Cycle VC Threshold VC=0.8V; VFB=VREF VC=0.8V; VFB=VREF, 3VVIN60V VC=0.8V; VFB=VREF VC=VFB=VREF VC=0.6V; 3VVIN60V VC=open, 1.0VVFB1.5V VC=VFB=VREF; VSW=15V VC=2V; VFB=open, VSW=15V VFB=open; VSW =15V, duty cycle=0% 1.214 1.244 350 2.6 6.0 25 40 92 0.90 1.274 0.03 1100 3.0 9.0 V %/V nA V mA mA/A kHz % V
33 0.60
47 1.25
s Error Amplifier Transconductance Source/Sink Current High Voltage Clamp Low Voltage Clamp Gain s Output Switch Breakdown Voltage On Resistance Control Voltage to Switch Current Transconductance Current Limit
VC=0.8V; VFB=VREF, IC=25A VC=1.5V VFB=1.0V VFB=1.5V 0.9VVC1.4V, VFB=VREF
2400 120
4400 200 2.0 0.38 800
7000 400
mho A V V V/V
VC=0.5V; 3VVIN60V, IOUT=5mA VC=open, VFB=0.8V, IOUT=1.25A 1.2VVC1.8V Duty Cycle50%, TJ25C Duty Cycle50%, TJ<25C Duty Cycle=80% Duty Cycle=80% (Note 1)
75
90 0.6 2
1.0
V A/V A A A A
1.25 1.25 1.00 0.50
3.00 3.50 2.50 2.50
Note 1: 16 lead SO wide package only.
2
CS3972
Package Pin Description
PACKAGE PIN # PIN SYMBOL FUNCTION
16L SO Wide 16 2 3 1,4,5,6,7,8, 10,12,15 9 11
5L TO-220 3 1 2
8L PDIP 1 2 3 4 Gnd VC VFB NC VIN E1 Logic and power ground on TO-220. Logic ground only on 8L PDIP. Control voltage can be used for frequency compensation, current limit threshold, frequency synchronization, and soft start. Feedback voltage is the negative input to the error amplifier. No connection. Supply input voltage with a range of 3V to 60V. Emitter One is a power ground which should always be connected to logic ground since it is used as the negative input to the current sense amp. Collector of internal 75V NPN power switch. Emitter Two is a power ground which can be left disconnected to reduce the switch rating to 625mA.
5
5 6
13 14
4
7 8
VSW E2
Typical Performance Characteristics
Reference Voltage vs. Temperature
1.274 1.264
Switching Frequency vs. Temperature
47 45
Driver Current vs. Switch Current
100 90 80
Reference Voltage (V)
Driver Current (mA)
-25 -0 25 50 75 100 125 150
1.254 1.244 1.234 1.224 1.214 -50
Frequency (kHz)
43 41 39 37 35 33 -50
70 60 50 40 30 20 10
-25
-0
25
50
75
100
125
150
0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Temperature (C)
Temperature (C)
Switch Current (A)
Maximum Duty Cycle
97 96
Switch Saturation Voltage
1.6 Tj=25C
Switch Saturation Voltage (V)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.0
Duty Cycle (%)
95 93 92 91 90 -50
-25
-0
25
50
75
100
125
150
Junction Temperature (C)
Switch Current (A)
3
CS3972
Circuit Description The CS3972 has an on board, high current NPN transistor in its output stage. The output transistor is switched on every 25s by the on board 40 kHz oscillator. The output is switched off as soon as the output current reaches a dynamically controlled level. That level is determined by three factors: the current drawn by the load, the input voltage, and the output voltage. This control scheme has several benefits. The IC reacts quickly to overvoltage and short circuit conditions and it is less sensitive to input voltage fluctuation. Current drawn by the load influences when the output stage turns off. The voltage across the internal high precision resistor (0.11) in the emitter of the output transistor generating the input to the current sensing amplifier. The output of the current sensing amplifier provides one of the inputs to the comparator. The other input to the comparator connected to the output of the error amplifier whose inverting input is connected to the output voltage through the feedback circuitry while its noninverting input is set to an internal reference voltage of 1.24V. When the current sensing amplifier output exceeds the error amplifier output, the comparator switches off, triggering the logic which turns off the output stage. All on board amplifier, logic and protection circuitry uses the internal 2.3V reference to minimize quiescent current drain (6mA) and permits IC operation down to 3V. The anti-saturation circuitry minimizes output switch turn off time and power dissipation, by keeping the power NPN at the edge of saturation.
Application Diagrams
VIN L1 D1 VOUT
VIN L1 VOUT
Q1
R2
R1
R3
VSW VIN
VSW VIN
CS3972
VC + C1 R1 C2 Gnd
VFB
(1.24V) + C3
+ C1 VC R2
CS3972
Gnd
VFB
(1.24V) + C3 R4
R3
D1 C2
Figure 1: Boost Regulator
Figure 2: Buck Regulator with the External Switch
VOUT1 VIN C4 R1 C1 + C6 VOUT2 D3 C5 1/2 OC1 R4 (1.24V) C2 + R1 VSW R4 R5 R6 C4 TR1 + +VIN C5 D1 TR1 + D2 C3 L1 VOUT
VIN
VSW VFB
VIN
CS3972
VC Gnd
VFB
CS3972
VC + C2 R2 C3
Gnd R5 -VIN R2 C3 D1 1/2 OC1 R3
U1 R7
Figure 3: Flyback Multiple Output Regulator
Figure 4: Isolated Forward Regulator
4
CS3972
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA
D Lead Count 8 Lead PDIP 16 Lead SO Wide Metric Max Min 10.16 9.02 10.50 10.10 English Max Min .400 .355 .413 .398
Thermal Data RJC RJA typ typ
5L TO-220 1.7 50
8L PDIP 52 100
16L SO Wide 23 105
C/W C/W
Plastic DIP (N); 300 mil wide
7.11 (.280) 6.10 (.240)
8.26 (.325) 7.62 (.300) 3.68 (.145) 2.92 (.115)
1.77 (.070) 1.14 (.045)
2.54 (.100) BSC
.356 (.014) .203 (.008)
0.39 (.015) MIN. .558 (.022) .356 (.014) Some 8 and 16 lead packages may have 1/2 lead at the end of the package. All specs are the same.
REF: JEDEC MS-001
D
Surface Mount Wide Body (DW); 300 mil wide
7.60 (.299) 7.40 (.291)
10.65 (.419) 10.00 (.394)
0.51 (.020) 0.33 (.013)
1.27 (.050) BSC
2.49 (.098) 2.24 (.088)
2.65 (.104) 2.35 (.093)
1.27 (.050) 0.40 (.016)
REF: JEDEC MS-013
0.32 (.013) 0.23 (.009) D 0.30 (.012) 0.10 (.004)
5
CS3972
Package Specification
5 Lead TO-220 (T) Straight 5 Lead TO-220 (TVA) Vertical
4.83 (.190) 4.06 (.160) 10.54 (.415) 9.78 (.385) 3.96 (.156) 3.71 (.146)
10.54 (.415) 9.78 (.385) 2.87 (.113) 6.55 (.258) 2.62 (.103) 5.94 (.234)
4.83 (.190) 4.06 (.160) 3.96 (.156) 3.71 (.146)
1.40 (.055) 1.14 (.045)
6.55 (.258) 5.94 (.234)
1.40 (.055) 1.14 (.045)
2.87 (.113) 2.62 (.103)
14.99 (.590) 14.22 (.560)
14.99 (.590) 14.22 (.560)
1.78 (.070) 2.92 (.115) 2.29 (.090)
14.22 (.560) 13.72 (.540)
8.64 (.340) 7.87 (.310) 0.56 (.022) 0.36 (.014)
4.34 (.171) 7.51 (.296) 1.68 (.066) typ 6.80 (.268)
1.70 (.067)
1.02 (.040) 0.76 (.030)
.94 (.037) .69 (.027)
1.02(.040) 0.63(.025) 6.93(.273) 6.68(.263)
1.83(.072) 1.57(.062)
0.56 (.022) 0.36 (.014) 2.92 (.115) 2.29 (.090)
5 Lead TO-220 (THA) Horizontal
4.83 (.190) 10.54 (.415) 9.78 (.385) 2.87 (.113) 2.62 (.103) 1.40 (.055) 3.96 (.156) 3.71 (.146) 1.14 (.045) 4.06 (.160)
6.55 (.258) 5.94 (.234)
14.99 (.590) 14.22 (.560)
2.77 (.109) 6.83 (.269)
0.81(.032)
1.68 (.066) TYP 1.70 (.067) 6.81(.268)
0.56 (.022) 0.36 (.014) 6.60 (.260) 5.84 (.230)
2.92 (.115) 2.29 (.090)
Ordering Information
Part Number CS3972YN8 CS3972YDW16 CS3972YDWR16 CS3972YT5 CS3972YTVA5 CS3972YTHA5
Rev. 6/23/99
Description 8L PDIP 16L SO Wide 16L SO Wide (tape & reel) TO-220 Straight TO-220 Vertical TO-220 Horizontal 6
Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information.
(c) 1999 Cherry Semiconductor Corporation

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