zero (in discontinuous mode). Under fault conditions

when the inductor current exceeds the 100mV current-

limit threshold, the high-side latch resets and the high-

side switch turns off.

At light loads, the inductor current fails to exceed the

25mV threshold set by the minimum current compara-

tor. When this occurs, the PWM goes into idle mode,

skipping most of the oscillator pulses in order to reduce

the switching frequency and cut back switching losses.

The oscillator is effectively gated off at light loads

because the minimum current comparator immediately

resets the high-side latch at the beginning of each

cycle, unless the FB_ signal falls below the reference

voltage level.

A flyback winding controller regulates the +15V VDD

supply in the absence of a load on the main 3.3V out-

put. If VDD falls below the preset +13V VDD regulation

threshold, a 1µs one-shot is triggered that extends the

low-side switch’s on-time beyond the point where the

inductor current crosses zero (in discontinuous mode).

This causes inductor (primary) current to reverse,

pulling current out of the output filter capacitor and

causing the flyback transformer to operate in the for-

ward mode. The low impedance presented by the

transformer secondary in forward mode allows the

+15V filter capacitor to be quickly charged up again,

bringing VDD into regulation.

Triple-Output Power-Supply Controller

for Notebook Computers

_______________________________________________________________________________________

9

VPPA

DA0

DA1

DB0

DB1

BST3

DH3

LX3

DL3

CS3

FB3

SS3

ON3

ON5

SHDN

VPPB

VDD

BST5

DH5

LX5

DL5

CS5

FB5

SS5

VH

D1-D2

Q1-Q2

9

11

10

24

22

23

25

21

27

20

5

3, 4

7, 6

16

15

18

17

31

33

32

30

35

34

36

1

19

GND

PGND

29

28

12

26

BATTERY INPUT

5.5V TO 30V

(NOTE 1)

VPP

CONTROL

INPUTS

C1

33

µF

D1A

C10

N1

L1

10

µH

R1

25m

Ω

+5V

at

3A

C3

330

µF

C4

330

µF

D2

1N5819

N2

C13

0.01

µF

+3.3V ON/OFF

+5V ON/OFF

SHUTDOWN

C15

1

µF

C7

4.7

µF

C8

1

µF

C9

1

µF

D1B

C11

0.1

µF

D3

EC11FS1

N3

1:4

L2 10

µH

D5

1N5819

N4

R2

20m

Ω

C12

2.2

µF

+3.3V

at

3A

C14

0.01

µF

2

2

COMPARATOR SUPPLY INPUT

COMPARATOR INPUTS

COMPARATOR OUTPUTS

OSCILLATOR SYNC

+5V at 5mA

0V, 3.3V, 5V, 12V

+15V AT 200mA, SEE

HIGH-SIDE SUPPLY (VDD)

SECTION.

0V, 3.3V, 5V, 12V

MAX783

V+

VL

C2

33

µF

C1–C6 = SPRAGUE 595D or AVX TPS SERIES

N1–N4 = Si9410DY or IRF7101 (BOTH SECTIONS)

D1A, D1B = LOW-POWER SCHOTTKY (CMPSH3 OR EQUIVALENT)

FOR V

NOTE 1: BATTERY VOLTAGE RANGE 6V to 20V WITH COMPONENTS SHOWN.

NOTE 2: KEEP KELVIN-CONNECTED CURRENT-SENSE TRACES SHORT AND CLOSE TOGETHER. SEE FIG.5.

NOTE 3: ZENER DIODE CLAMP REQUIRED FOR VIN

Ω PULL-DOWN OR OTHER 1mA MINIMUM LOAD.

(NOTE 2)

(NOTE 2)

0.1

µF

D6

18V

100mW (NOTE 3)

C5

150

µF

C6

150

µF

3.3V AT 5mA

5V POWERGOOD

SYNC

REF

RDY5

2

8

14

13

Figure 1. Standard Application Circuit