MAX782CSLASHD datasheet(24/32 Pages) MAXIM

24 / 32 page

Triple-Output Power-Supply

Controller for Notebook Computers

______________________________________________________________________________________

Total Shutdown Circuits

When the +5V and +3.3V supplies are off, the complete

MAX782 circuit consumes only about 70µA, plus any

leakage through the off MOSFETs. Some NiCd batter-

ies can be damaged if they are fully discharged and

then left for long periods (months) under load. Even

100µA can do damage if left long enough.

The complete power-supply system can be shut down

by taking ON5 low, cutting the supply to the MAX782’s

V+ pin, while the bootstrapped +5V supply is turned

off. This removes the supply from the controller, and

turns off all the supplies. In this condition, the current

consumption drops to the level of the leakage currents

in the off transistors. Switching the V+ supply off is

easy because the V+ line draws very little power;

switching the entire power input from the battery would

be more difficult.

Figure 12 shows a logic interface for a momentary

switch that toggles the whole system on and off. The

logic circuit runs from the battery supply, so the input

voltage from the battery is limited to the normal operat-

ing range for the flip-flop gates, which is usually 18V for

4000-series CMOS circuits. The active-high OFF input

permits the supplies to be turned off under logic control

as well as when the switch is pushed. If this logic input

is not required, omit R1 and Q1. The supplies can only

be turned on using the hardware switch. For automatic

turn-off, connect the OFF input to a battery-voltage

sensing comparator or to a timer powered from VL.

Ensure that any signal connected to OFF does not

glitch high at power-up.

Generating Additional VPP Outputs

Using External Linear Regulators

Figure 13 shows a low-dropout linear regulator

designed to provide an additional VPP output from the

VDD line. It can be turned off with a logic-level signal;

its output can be switched to 5V or 12V; and it pro-

vides excellent rejection of the high-frequency noise

on VDD. If a monolithic linear regulator is used,

choose one having good PSRR performance at

300kHz.

ZETEX

ZVP2106G

SOT 223

VBATT

ON/

OFF

µF

CD4011B

1N4148

µF

OFF

2N4401

ON5

1N4148

PGND

(+5.5V TO +18V)

1N4148

ON5

V+

MAX782

1N4148

Figure 12. Hardware/Software Total Shutdown Circuit

2N7002

2N4403

100nF

10nF

16.9k

OUT

6.8

µF

6.34k

26.7k

2N7002

12/5

OFF/ON

100k

REF

10nF

VDD

OP27

OFF/ON

12/5

VOUT (V)

X = DON'T CARE

FROM MAX782

Figure 13. External Regulator For Additional VPP Outputs

MAX782C/D Datasheet(PDF) 24 Page - Maxim Integrated Products

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