MAX1902 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX1902

500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers

Maxim Integrated 

500kHz Multi-Output, Low-Noise Power-Supply

Controllers for Notebook Computers

Standard Application Circuit

The basic MAX1901/MAX1904 dual-output 3.3V/5V

buck converter (Figure 1) is easily adapted to meet a

wide range of applications with inputs up to 28V by

substituting components from Table 1. These circuits

represent a good set of tradeoffs between cost, size,

and efficiency, while staying within the worst-case

specification limits for stress-related parameters, such

as capacitor ripple current. Don’t change the frequency

of these circuits without first recalculating component

values (particularly inductance value at maximum bat-

tery voltage). Adding a Schottky rectifier across each

synchronous rectifier improves the efficiency of these

circuits by approximately 1%, but this rectifier is other-

wise not needed because the MOSFETs required for

these circuits typically incorporate a high-speed silicon

diode from drain to source. Use a Schottky rectifier

rated at a DC current equal to at least one-third of the

load current.

Detailed Description

The MAX1901/MAX1902/MAX1904 are dual, BiCMOS,

switch-mode power-supply controllers designed pri-

marily for buck-topology regulators in battery-powered

applications where high-efficiency and low-quiescent

supply current are critical. Light-load efficiency is

enhanced by automatic Idle-Mode operation, a vari-

able-frequency pulse-skipping mode that reduces tran-

sition and gate-charge losses. Each step-down,

power-switching circuit consists of two N-channel

MOSFETs, a rectifier, and an LC output filter. The out-

put voltage is the average AC voltage at the switching

node, which is regulated by changing the duty cycle of

the MOSFET switches. The gate-drive signal to the

N-channel high-side MOSFET must exceed the battery

voltage, and is provided by a flying-capacitor boost cir-

cuit that uses a 100nF capacitor connected to BST_.

Table 1. Component Selection for Standard 3.3V/5V Application

COMPONENT

Input Range

Frequency

Q1, Q3 High-Side

MOSFETs

Q2, Q4 Low-Side

MOSFETs with Integrated

Schottky Diodes

C3 Input Capacitor

C1 Output Capacitor

C2 Output Capacitor

R1, R2 Resistors

L1 Inductor

L2 Inductor

4A/333kHz

7V to 24V

333kHz

1/2 Fairchild FDS6982S or

1/2 International Rectifier

IRF7901D1

1/2 Fairchild FDS6982S or

1/2 International Rectifier

IRF7901D1

3 ✕ 10µF, 25V ceramic

Taiyo Yuden TMK432BJ106KM

150µF, 6V POSCAP

Sanyo 6TPC150M

2 ✕ 150µF, 4V POSCAP

Sanyo 4TPC150M

0.018Ω

Dale WSL2512-R018-F

10µH, 4.5A Ferrite

Sumida CDRH124-100

7.0µH, 5.2A Ferrite

Sumida CEI122-H-7R0

LOAD CURRENT

4A/500kHz

7V to 24V

500kHz

1/2 Fairchild FDS6982S or

1/2 International Rectifier

IRF7901D1

1/2 Fairchild FDS6982S or

1/2 International Rectifier

IRF7901D1

3 ✕ 10µF, 25V ceramic

Taiyo Yuden TMK432BJ106KM

150µF, 6V POSCAP

Sanyo 6TPC150M

2 ✕ 150µF, 4V POSCAP

Sanyo 4TPC150M

0.018Ω

Dale WSL2512-R018-F

7.0µH, 5.2A Ferrite

Sumida CEI122-H-7R0

5.6µH, 5.2A Ferrite

Sumida CEI122-H-5R6

6A/500kHz

7V to 24V

500kHz

Fairchild FDS6612A or

International Rectifier

IRF7807V

Fairchild FDS6670S or

International Rectifier

IRF7807DV1

4 ✕ 10µF, 25V ceramic

Taiyo Yuden TMK432BJ106KM

2 ✕ 150µF, 6V POSCAP

Sanyo 6TPC150M

2 ✕ 220µF, 4V POSCAP

Sanyo 4TPC220M

0.012Ω

Dale WSL2512-R012-F

4.2µH, 6.9A Ferrite

Sumida CEI122-H-4R2

4.2µH, 6.9A Ferrite

Sumida CEI122-H-4R2

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