UNITRODE UCC1570, UCC2570, UCC3570 Technical data

UCC1570

UCC2570

UCC3570

Low Power Pulse Width Modulator

FEATURES

∙Low Power BiCMOS Process

∙85μA Start-up Current

∙1mA Run Current

∙1A Peak Gate Drive Output

∙Voltage Feed Forward

∙Programmable Duty Cycle Clamp

∙Optocoupler Interface

∙500kHz Operation

∙Soft Start

∙Fault Counting Shutdown

∙Fault Latch Off or Automatic Restart

DESCRIPTION

The UCC1570 family of pulse width modulators is intended for application in isolated switching supplies using primary side control and a voltage mode feedback loop. Made with a BiCMOS process, these devices feature low startup current for efficient off-line starting with a bootstrapped low voltage supply. Operating current is also very low; yet these devices maintain the ability to drive a power MOSFET gate at frequencies above 500kHz.

Voltage feedforward provides fast and accurate response to wide line voltage variation without the noise sensitivity of current mode control. Fast current limiting is included with the ability to latch off after a programmable number of repetitive faults has occurred. This allows the power supply to ride through a temporary overload, while still shutting down in the event of a permanent fault. Additional versatility is provided with a maximum duty cycle clamp programmable within a 20% to 80% range and line voltage sensing with a programmable window of allowable operation.

BLOCK DIAGRAM

CLOCK

CLK

FREQ

GENERATOR

RAMP

4.5V

VALLEY

VFWD

10 I3

VREF

GENERATOR

SLOPE

GND

RAMP

LATCH

15V

ISET

10 I4

13/9V

RAMP

HIGH

PEAK

VCC

LINE

LOW

LINE

OUT

FEEDBK

PWM

PGND

PWM

LATCH

SOFTST

CURRENT

CURLIM

LIMIT

0.2V

CLK

COUNT

SHUTDOWN

LATCH

SHUTDOWN

0.6V

04/99

UNITRODE UCC1570, UCC2570, UCC3570 Technical data

ABSOLUTE MAXIMUM RATINGS

Supply Voltage

(Limit Supply Current to 20mA) . . . . . . . Self Limiting at 15V

Supply Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +20mA

Analog Inputs (CURLIM, VFWD, FEEBK) . . . . . . . . . . . . . . 6V

Programming Current ISLOPE, IISET . . . . . . . . . . . . . . . . . –1mA Output Current IOUT

DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±180mA Pulse (0.5ms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1.2A

Note: All voltages are with respect to GND. Currents are positive into the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of package.

PLCC-20 (TOP VIEW)

Q Package

ORDERING INFORMATION

	Temperature Range	Package
UCC1570J	–55°C to +125°C	Ceramic Dip
UCC2570D	–40°C to +85°C	SOIC
UCC2750N		Plastic Dip
UCC3570D	0°C to +70°C	SOIC
UCC3570N		Plastic Dip
UCC3570Q		PLCC

UCC1570

UCC2570

UCC3570

CONNECTION DIAGRAMS

DIL-14 (TOP VIEW)

N or J Package

SOIC-14 (TOP VIEW)

D Package

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = 0 to 70°C for the

UCC3570, TA= –40 to 85°C for the UCC2570, TA=–55 to 125°C for the UCC1570, RISET=100k, RSLOPE=121k, CFREQ=180pF, CRAMP=150pF, VCC=11V and TA=TJ.

PARAMETER	TEST CONDITIONS	Min	Typ	Max	Units
Reference
VREF	VCC =10 to 13V, IVREF = 0 to 2mA	4.9	5	5.1	V
Line Regulation	VCC = 10 to 13V		2	10	mV
Load Regulation	IVREF = 0 to 2mA		2	10	mV
Short Circuit Current	VREF = 0		10	50	mA
VCC
Vth (On)		12	13		V
Vth (Off)		8	9	10	V
Hysteresis		3	4	5	V
VCC	IVCC = 10mA	13.5	15	16	V
IVCC Start	VCC = 11V, VCC Comparator Off		85	150	μA
IVCC Run	VCC Comparator On		1	1.5	mA

UCC1570

UCC2570

UCC3570

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = 0 to 70°C for the

UCC3570, TA= –40 to 85°C for the UCC2570, TA=–55 to 125°C for the UCC1570, RISET=100k, RSLOPE=121k, CFREQ=180pF, CRAMP=150pF, VCC=11V and TA=TJ.

PARAMETER	TEST CONDITIONS	Min	Typ	Max	Units
Line Sense
Vth High Line Comparator		3.9	4	4.1	V
Vth Low Line Comparator		0.96	1	1.04	V
lib (VFWD)			0	±100	nA
Oscillator
Frequency		90	100	110	kHz
Ramp Generator
IRAMP/ISLOPE		9	10	11	A/A
–IRAMP/IISET		9	10	11	A/A
Peak Ramp Voltage		3.8	4	4.2	V
Valley Ramp Voltage		0.95	1	1.05	V
ISET Voltage Level		0.95	1	1.05	V
Soft Start
Saturation	VCC = 11V, VCC Comparator Off		25	100	mV
ISOFTST/IISET		0.8	1	1.2	A/A
Pulse Width Modulator
lib(FEEDBK)			0	±100	n A
FEEDBK	Zero Duty Cycle	0.9	1	1.1	V
	Maximum Duty Cycle, (Note 1)	3.8	4	4.2	V
Current Limit
lib(CURLIM)			0	±100	nA
Vth Current Limit		180	200	220	mV
Vth Shutdown		500	600	700	mV
Fault Counter
Vth		3.8	4	4.2	V
Vsat			0	100	mV
ICOUNT/IISET		0.8	1	1.2	A/A
Output Driver
Vsat High	IOUT = –100mA		0.4	1	V
Vsat Low	IOUT = 100mA		0.4	1	V
Rise/Fall Time	COUT = 1nF, (Note 1)		20	100	ns

Note 1: This parameter guaranteed by design but not 100% tested in production.

PIN DESCRIPTIONS

VCC: Chip supply voltage pin. Bypass to PGND with a low ESL/ESR 0.1μF capacitor plus a capacitor for gate charge storage. Lead lengths must be minimum.

PGND: Ground pin for the output driver. Keep connections less than 2cm. Carefully maintain low impedance path for high current return.

OUT: Gate drive output pin. Connect to the gate of a power MOSFET with a resistor greater than 2Ω. Keep connection lengths under 2cm.

VFWD: Voltage Feed Forward and Line Sense pin. Connect to input DC line using a resistive divider.

SLOPE: Program the charging current for RAMP with a resistor from this pin to GND. This pin will follow VFWD.

FEEDBK: Input to the pulse width modulator comparator. Drive this pin with an optocoupler to GND and a resistor to VREF. Modulation input range is from 1V to 4V.

ISET: A resistor from this pin to GND programs RAMP discharge current, FREQ current, SOFTST current, and COUNT current.

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