Rainbow-electronics MAX1855 Bedienungsanleitung PDF herunterladen (Seite 30)

MAX1716/MAX1854/MAX1855

High-Speed, Adjustable, Synchronous Step-Down

Controllers with Integrated Voltage Positioning

30 ______________________________________________________________________________________

3) Group the gate-drive components (BST diode and

capacitor, V

bypass capacitor) together near the

controller IC.

4) Make the DC-DC controller ground connections as

shown in Figure 1. This diagram can be viewed as

having three separate ground planes: output ground,

where all the high-power components go; the GND

plane, where the GND pin and V

bypass capaci-

tors go; and an analog ground plane where sensitive

analog components go. The analog ground plane

and GND plane must meet only at a single point

directly beneath the IC. These two planes are then

connected to the high-power output ground with a

short connection from GND to the source of the low-

side MOSFET (the middle of the star ground). This

point must also be very close to the output capacitor

ground terminal.

5) Connect the output power planes (V

CORE

and sys-

tem ground planes) directly to the output filter

capacitor positive and negative terminals with multi-

ple vias. Place the entire DC-DC converter circuit as

close to the CPU as is practical.

___________________Chip Information

TRANSISTOR COUNT: 3729

OUT

(4) 220µF

1.0µH

1.3V OUTPUT

UP TO 12A

SHDN

VGATE

1µF

0.1µF

1µF

10Ω

(4) 10µF

BATTERY (V

BATT

)

7V TO 24V

REF

ILIM

+5V INPUT

BIAS SUPPLY

POWER-GOOD

INDICATOR

V+

BST

PGND

VPS

TON

MAX1716

MAX1854

MAX1855

SKIP

GND

100kΩ

TO V

100kΩ

300kΩ

47pF

0.22µF

ON OFF

2kΩ

FLOAT (300kHz)

1kΩ

SENSE

3.5mΩ

Q1: IRF7811

INTERNATIONAL RECTIFIER

Q2: (2) IRF7811

INTERNATIONAL RECTIFIER

D1: CMPSH-3

CENTRAL SEMICONDUCTOR

D2: CMSH2-60

CENTRAL SEMICONDUCTOR

MAX1716 DAC CODE SHOWN

Figure 11. Low-Current Application (Circuit #2)

1 2 ... 25 26 27 28 29 30 31 32 33

MAX1716/MAX1854/MAX1855 1

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