ISL6740_14 Datasheet, PDF(21/28 Page) Intersil Corporation – Flexible Double Ended Voltage and Current Mode PWM Controllers

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ISL6740_14 Datasheet, PDF (21/28 Pages) Intersil Corporation – Flexible Double Ended Voltage and Current Mode PWM Controllers

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ISL6740, ISL6741

Component List

REFERENCE

DESIGNATOR VALUE

DESCRIPTION

1.0Î¼F Capacitor, 1812, X7R, 100V, 20%

TDK C4532X7R2A105M

C2, C3

3.3Î¼F Capacitor, 1812, X5R, 50V, 20%

TDK C4532X5R1H335M

C4, C6

1.0Î¼F Capacitor, 0805, X5R, 16V, 10%

TDK C2012X5R1C105K

C5, C15, C16 0.1Î¼F Capacitor, 0603, X7R, 50V, 10%

TDK C1608X7R1H104K

Open Capacitor, 0603, Open

22Î¼F Capacitor, 1812, X5R, 16V, 20%

TDK C4532X5R1C226M

150Î¼F Capacitor, Radial, Sanyo 16SH150M

C10, C11, C12, 1000pF Capacitor, 0603, X7R, 50V, 10%

C13, C14

TDK C1608X7R1H102K

C17

220pF Capacitor, 0603, COG, 16V, 5%

TDK C1608COG1C221J

C18

0.047Î¼F Capacitor, 0603, X7R, 16V, 10%

TDK C1608X7R1C473K

CR1, CR2

CR3

190nH

1.5Î¼H

Short

Diode, Schottky, BAT54S

Diode, Schottky, BAT54

Zener, 10V, Philips BZX84-C10

Pulse, P2004T

Pulse, PG0077.142

Jumper or Optional Discrete Leakage

Inductance

QL, QH

QR1, QR2, QR3,

QR4

R1, R10

3.3

3.01k

R3, R6

10.0

3.32

75.0k

R8, R9

20.0

R11

100

R12

8.06k

R13

17.4k

R14

Open

R15

1.27k

R17

97.6k

R18

3.01k

R19, RT1

10.0k

Transistor, ON MJD31C

FET, Fairchild FDS3672

FET, Fairchild FDS5670

Resistor, 2512, 5%

Resistor, 2512, 1%

Resistor, 0603, 1%

Resistor, 0805, 1%

Resistor, 0603, 1%

Resistor, 0603, Open

Resistor, 0603, 1%

Midcom 31718

Pulse P8205T

Intersil HIP2101IB

ISL6740IB

Adding Line Only Regulation - Feed Forward

Output voltage variation caused by changes in the supply voltage

may be virtually removed through a technique known as feed

forward compensation. Using feed forward, the duty cycle is

directly controlled based on changes in the input voltage only. No

closed loop feedback system is required. Voltage feed forward

may be implemented as shown in Figure 18.

R109

3.48k

VREF

+VIN

R110

698

R111

806

1.5V

0.8V

R100

69.8k

R101

R102

100k

R103

49.9k

R106

100K

+ U100A

R105

100k

R104

100k

U100B

C100

1nF

R107

100k

R108

100k

to VERROR

FIGURE 18. VOLTAGE FEED FORWARD CIRCUIT

The circuit provides feed forward compensation for a 2:1 input

voltage range. Resistors R100 and R101 set the input voltage

divider to generate a 1V signal at the input voltage that

corresponds to maximum duty cycle (VIN minimum). Resistors

R109, R110, and R111 form a voltage divider from VREF to create

reference voltages for the amplifiers. The first stage uses U100A,

R102, R103, R104, and C100 to form a unity gain inverting

amplifier. Its output varies inversely with input voltage and

ranges from 1V to 2V. The bandwidth of the circuit may be

controlled by varying the value of C100. The gain of the first

amplifier stage is:

VA = âVD + 3.00

(EQ. 25)

where:

VA = Output voltage of U100A

VD = The input divider voltage

The second stage uses U100B, R105, R106, R107, and R108 to

form a summing amplifier which offsets the first stage output by

0.8V (the value of CT valley voltage). The signal applied to the

VERROR input now matches the offset and amplitude of the

oscillator sawtooth so that the duty cycle varies linearly from

100% to 50% of maximum with a 2:1 input voltage variation.

FN9111.6

December 2, 2011

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