LT1950IGN datasheet(8/20 Pages) LINER

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LT1950

sn1950 1950fs

The LT1950 is a constant frequency, current mode con-

troller for DC/DC forward, boost, flyback and SEPIC con-

verter applications. The Block Diagram in Figure 1 shows

all of the key functions of the IC.

In normal operation, a VIN voltage as low as 3V allows an

internal switcher at the BOOST pin to generate a separate

BLOCK DIAGRA

OPERATIO

Figure 1. LT1950 Block Diagram

–

VREF =

INTERNAL +

EXTERNAL

SUPPLY

VIN2

2.5V

(SOURCE 2.5mA

EXTERNALLY)

1.23V

(VIN) (2.6V)

U/V LOCKOUT

(VIN2) (8V)

U/V LOCKOUT

(100-500)khz

(105/VSEC)%

OSC

(TYPICAL 200kHz)

SHDN

SYNC

ROSC

SLOPE

1.32V

1.23V

MAX DC

CLAMP

SLOPE COMP

RAMP

BLANKING

COMP

GND

BLANK

VREF

VIN

VSEC

BOOST

VIN2

SWITCHING PREREGULATOR

FIXED OFF TIME

(125mA CURRENT LIMIT)

PGND

DISABLE

–

CURRENT

SENSE

CMP

BLANKING

OVERRIDE

CMP

GATE

PGND

ISENSE

±1A

DRIVER

13V

ENABLE

11V

1950 BD

µA

ERROR AMPLIFIER

VOLTAGE GAIN = 85dB

125mV

0mV – >100mV

11V supply at VIN2 using a small surface mount external

inductor, diode and capacitor. Since VIN2 supplies the

output driver of the IC, this architecture achieves high

GATE drive for an external N-channel power MOSFET even

though VIN voltage is very low. High GATE drive capability

reduces MOSFET RDS(ON) for improved efficiency,

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