LT1950 데이터 시트보기 (PDF) - Linear Technology

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LT1950

Single Switch PWM Controller with Auxiliary Boost Converter

Linear Technology 

LT1950

BLOCK DIAGRA

VIN

VREF

VSEC BOOST

15

6

16

14

1.23V

VIN2

VREF =

INTERNAL +

EXTERNAL

SUPPLY

2.5V

(SOURCE 2.5mA

EXTERNALLY)

(VIN) (2.6V)

U/V LOCKOUT

SWITCHING PREREGULATOR

FIXED OFF TIME

(125mA CURRENT LIMIT)

DISABLE

PGND

(VIN2) (8V)

U/V LOCKOUT

(105/VSEC)%

VIN2

11

11V

8V

+–

SHDN 7

SYNC 4

ROSC 3

SLOPE 5

1.32V

3µA

(TYPICAL 200kHz)

OSC

(100-500)khz

RAMP

ERROR AMPLIFIER

1.23V + VOLTAGE GAIN = 85dB

–

–

MAX DC

+ CLAMP

ENABLE

S

SLOPE COMP

R

–

Q

±1A

+DRIVER

12 GATE

13 PGND

BLANKING

CURRENT

SENSE

CMP

–+

0mV – >100mV

13V

BLANKING

OVERRIDE

CMP

–+

125mV

10 ISENSE

2

1

8

FB

COMP

GND

9

BLANK

1950 BD

Figure 1. LT1950 Block Diagram

U

OPERATIO

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

8

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,

1950fa

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