MAXM17543_V01 datasheet(17/20 Pages) MAXIM

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Mode Selection (MODE)

The MAXM17543 features a MODE pin to configure the

device operating in PWM, PFM, or DCM control schemes.

The device operates in PFM mode at light loads if the

MODE pin is open. If the MODE pin connects to ground,

the device operates in constant-frequency PWM mode at

all loads. The device operates in constant-frequency DCM

mode at light loads when the MODE pin connects to VCC.

State changes of the MODE operation are only at power-

up and ignore during normal operation.

PWM Mode Operation

In PWM mode, the step-down controller is switching

a constant-frequency at all loads with a minimum sink

current limit threshold (-1.8A typ) at light load. The

PWM mode of operation gives lower efficiency at light

loads compared to PFM and DCM modes of operation.

However, the PWM mode of operation is useful in applica-

tions sensitive to switching frequency.

PFM Mode Operation

In PFM mode, the controller forces the peak inductor

current in order to feed the light loads and maintain high

efficiency. If the load is lighter than the average PFM

value, the output voltage will exceed 102.3% of the feed-

back threshold and the controller enters into a hibernation

mode, turning off most of the internal blocks. The device

exits hibernation mode and starts switching again once the

output voltage is discharged to 101.1% of the feedback

threshold. The device then begins the process of delivering

pulses of energy to the output repeatedly until it reaches

102.3% of the feedback threshold. In this mode, the

behavior resembles PWM operation (with occasional pulse

skipping), where the inductor current does not need to

reach the light-load level.

PFM mode offers the advantage of increased efficiency at

light loads due to a lower quiescent current drawn from the

supply. However, the output-voltage ripple is also increased

as compared to the PWM or DCM modes of operation, and

the switching frequency is not constant at light loads.

DCM Mode Operation

DCM mode features constant frequency operation down

to lighter loads than PFM mode, accomplished by not

skipping pulses. DCM efficiency performance lies between

the PWM and PFM modes.

External Frequency Synchronization (SYNC)

The device can be synchronized by an external clock

signal on the SYNC pin. The external synchronization

clock frequency must be between 1.1 x fSW and 1.4 x

fSW, where fSW is the frequency programmed by the RT

resistor. The minimum external clock high pulse width

and amplitude should be greater than 50ns and 2.1V,

respectively. The minimum external clock low pulse

width should be greater than 160ns, and the maximum

external clock low pulse amplitude should be less than 0.8V.

Table 1 provides recommended synchronous frequency

ranges for desired output voltages. Connect the SYNC

pin to SGND if it is not used.

RESET Output

The device includes a RESET comparator to monitor the

output for undervoltage and overvoltage conditions. The

open-drain RESET output requires an external pullup

resistor from 10kΩ to 100kΩ to VCC pin or maximum 6V

voltage source. RESET goes high impedance after the

regulator output increases above 95% of the designed nomi-

nal regulated voltage. RESET goes low when the regulator

output voltage drops below 92% of the nominal regulated

voltage. RESET also goes low during thermal shutdown.

Overcurrent Protection (OCP)

The MAXM17543 is provided with a robust overcurrent

protection (OCP) scheme that protects the module under

overload and output short-circuit conditions. A cycle-by-

cycle peak current limit turns off the high-side MOSFET

whenever the high-side switch current exceeds an inter-

nal limit of 3.7A (typ). The module enters hiccup mode

of operation either after one occurrence of the runaway

current limit 4.3A (typ) or when the FB node goes below

0.58V of its nominal regulation threshold after soft-start

is complete. In hiccup mode, the module is protected

by suspending switching for a hiccup timeout period of

32,768 clock cycles. Once the hiccup timeout period

expires, soft-start is attempted again. Hiccup mode of

operation ensures low power dissipation under output

overload or short-circuit conditions. Note that when soft-

start is attempted under overload condition, if feedback

voltage does not exceed 0.58V, the device switches at

half the programmed switching frequency.

The MAXM17543 is designed to support a maximum

load current of 2.5A. The inductor ripple current is

calculated as follows:

OUT

0.395 I

0.220 I

L f

0.175 I







−

∆=







−







where,

VOUT = Steady-state output voltage

VIN = Operating input voltage

www.maximintegrated.com

Maxim Integrated │ 17

MAXM17543

4.5V to 42V, 2.5A High-Efficiency, DC-DC Step-Down

Power Module with Integrated Inductor

MAXM17543 Datasheet(PDF) 17 Page - Maxim Integrated Products

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