Dual-Output Power-Supply

Controller for Notebook Computers

______________________________________________________________________________________

13

Table 1. Surface-Mount Components

(See Figure 1 for Standard Application Circuit.)

Internal VL and REF Supplies

An internal linear regulator produces the 5V used by the

internal control circuits. This regulator’s output is avail-

able on pin VL and can source 5mA for external loads.

Bypass VL to GND with 4.7µF. To save power, when the

+5V switch-mode supply is above 4.5V, the internal lin-

ear regulator is turned off and the high-efficiency +5V

switch-mode supply output is connected to VL.

The internal 3.3V bandgap reference (REF) is powered

by the internal 5V VL supply. It can furnish up to 5mA.

Bypass REF to GND with 0.22µF, plus 1µF/mA of load

current. The main switching outputs track the reference

voltage. Loading the reference will reduce the main

outputs slightly, according to the reference load-regula-

tion error.

Both the VL and REF outputs remain active, even when

the switching regulators are turned off, to supply mem-

ory keep-alive power (see

Shutdown Mode section).

These linear-regulator outputs can be directly connected

to the corresponding step-down regulator outputs (i.e.,

REF to +3.3V, VL to +5V) to keep the main supplies alive

in standby mode. However, to ensure start-up, standby

load currents must not exceed 5mA on each supply.

Fault Protection

The +3.3V and +5V PWM supplies and the compara-

tors are disabled when either of two faults is present:

VL < +4.0V or REF < +2.8V (85% of its nominal value).

__________________Design Procedure

Figure 1’s schematic and Table 2’s component list

show values suitable for a 3A, +5V supply and a 3A,

+3.3V supply. This circuit operates with input voltages

from 6.5V to 30V, and maintains high efficiency with

output currents between 5mA and 3A (see the

Typical

Operating Characteristics). This circuit’s components

may be changed if the design guidelines described in

this section are used — but before beginning the

design, the following information should be firmly

established:

COMPONENT

SPECIFICATION

MANUFACTURER

PART NO.

C1, C10

33µF, 35V tantalum capacitors

AVX

TPSE226M035R0100

Sprague

595D336X0035R

C2

4.7µF, 6V tantalum capacitor

AVX

TAJB475M016

Sprague

595D475X0016A

C3

1µF, 20V tantalum capacitor

AVX

TAJA105M025

Sprague

595D105X0020A2B

C4, C5

0.1µF, 16V ceramic capacitors

Murata-Erie

GRM42-6X7R104K50V

C6

330µF, 10V tantalum capacitor

Sprague

595D337X0010R

C7, C12

150µF, 10V tantalum capacitors

Sprague

595D157X0010D

C8, C9

0.01µF, 16V ceramic capacitors

Murata-Erie

GRM42-6X7R103K50V

D2A, D2B

1N4148-type dual diodes

Central Semiconductor

CMPD2836

D1, D3

1N5819 SMT diodes

Nihon

EC10QS04

L1, L2

10µH, 2.65A inductors

Sumida

CDR125-100

N1–N4

N-channel MOSFETs (SO-8)

Siliconix

Si9410DY

R1, R2

0.025

Ω, 1% (SMT) resistors

IRC

LR2010-01-R025-F

COMPANY

FACTORY FAX

USA PHONE

[COUNTRY CODE]

AVX

[1] (803) 626-3123

(803) 946-0690

(800) 282-4975

Central Semiconductor

[1] (516) 435-1824

(516) 435-1110

IRC

[1] (512) 992-3377

(512) 992-7900

Murata-Erie

[1] (814) 238-0490

(814) 237-1431

Nihon

[81] 3-3494-7414

(805) 867-2555

Siliconix

[1] (408) 970-3950

(408) 988-8000

Sprague

[1] (603) 224-1430

(603) 224-1961

Sumida

[81] 3-3607-5144

(847) 956-0666

Table 2. Component Suppliers