4.5V to 28V Input, Synchronous PWM Buck Controllers

for DDR Termination and Point-of-Load Applications

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11

Pin Description

PIN

MAX8553

MAX8554

FUNCTION

EN/HSD

—

Enable/High-Side Drain. Connect to the high-side N-channel MOSFET drain through a 5.1k

Ω

resistor for normal operation. Connect to GND for low-power shutdown (Figure 2). If the enable

function is not used, connect EN/HSD directly to the high-side N-channel MOSFET drain.

1

—

HSD

High-Side Drain. Connect to the high-side N-channel MOSFET drain for normal operation.

REFIN

—

range is from 0 to +3.6V.

2

—

EN

Enable. Drive EN high to enable the output. Drive EN low to shut down the IC. If the enable

function is not used, connect EN to V+.

3

POK

POK

Power-OK Output. POK is an open-drain output and is logic high when both VTT and VTTR are

within 12% of regulation. POK is pulled low in shutdown.

VTT

—

VTT Feedback Input. Connect to VTT output.

4

—

FB

Output Feedback. Connect to the center of a resistor-divider between the output and ground to

set the output voltage. FB threshold is 0.6V.

5

ILIM

ILIM

Current-Limit Threshold Adjustment. Connect a resistor from ILIM to GND to set the current-limit

threshold, or connect ILIM to VL for the default setting. See the Setting the Current Limit section.

6

FSEL

FSEL

Frequency Select. Selects the switching frequency. See Tables 1 and 2 for configuration of

FSEL.

7

REF

REF

Reference. Connect a 0.22µF or greater capacitor from REF to GND.

8

GND

GND

Ground

VTTR

—

VTTR Reference Output. Connect a 1µF or greater capacitor from VTTR to GND. VTTR is

capable of sourcing and sinking up to 25mA.

9

—

OUT

Output Voltage. Connect directly to the output. OUT senses the output voltage to determine the

on-time for the high-side switching MOSFET.

10

V+

V+

Input Supply Voltage. Supply input for the VL regulator. Bypass with a 0.22µF or greater

capacitor.

11

VL

VL

Internal Regulator Output. Connect a 2.2µF or greater capacitor from VL to GND. VL can be

connected to V+ if the operating range is from +4.5V to +5.5V.

12

DL

DL

Low-Side MOSFET Gate Drive. Connect to the gate of the low-side N-channel MOSFET. DL is

low in shutdown or in undervoltage lockout.

13

PGND

PGND

Power Ground

14

BST

BST

Bootstrapped Supply. Drives high-side N-channel MOSFET. Connect a 0.1µF or greater

capacitor from BST to LX.

15

DH

DH

High-Side MOSFET Gate Drive. Connect to the high-side N-channel MOSFET gate. DH is low in

shutdown or in undervoltage lockout.

16

LX

LX

Inductor Switching Node