MAX5083ATE datasheet(9/18 Pages) MAXIM

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Soft-Start and Reference (SS)

SS is the 1.23V reference bypass connection for the

MAX5082/MAX5083 and also controls the soft-start peri-

od. At startup, after VIN is applied and the internal and

external UVLO thresholds are reached, the device enters

soft-start. During soft-start, 15μA is sourced into the

capacitor (CSS) connected from SS to SGND causing the

reference voltage to ramp up slowly. When VSS reaches

1.23V the output becomes fully active. Set the soft-start

time (tSS) using the following equation:

1.23V C

15µA

where tSS is in seconds and CSS is in Farads.

Internal Charge Pump (MAX5082)

The MAX5082 features an internal charge pump to

enhance the turn-on of the internal MOSFET, allowing

for operation with input voltages down to 4.5V. Connect

a flying capacitor (CF) between C+ and C-, a boost diode

from C+ to BST, as well as a bootstrap capacitor (CBST)

between BST and LX to provide the gate-drive voltage

for the high-side n-channel DMOS switch. During the on-

time, the flying capacitor is charged to VDVREG. During

the off-time, the positive terminal of the flying capacitor

(C+) is pumped to two times VDVREG and charge is

dumped onto CBST to provide twice the regulator voltage

across the high-side DMOS driver. Use a ceramic capaci-

tor of at least 0.1μF for CBST and CF located as close to

the device as possible.

For applications that do not require a 4.5V minimum input,

use the MAX5083. In this device, the charge pump is

Figure 2. MAX5083 Simplified Block Diagram

1.23V

ON/OFF

LDO

REG

THERMAL

SHDN

REF

0.3V

CLK

ILIM

1.23V

REGOK

VREF

ISS

>1.23V ON

<1.11V OFF

COMP

SYNC

E/A

SSA

CPWM

RAMP

LOGIC

OSC

BOOTSTRAP

CONTROL

PCLK

BST

SGND

DVREG

PGND

SCLK

HIGH-SIDE

CURRENT

SENSE

REF_PFM

PFM

REF_ILIM

ILIM

OVERL

CLK

ILIM

OVERLOAD

MANAGEMENT

MAX5083

MAX5082/MAX5083

1.5A, 40V, MAXPower Step-Down

DC-DC Converters

www.maximintegrated.com

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