LTM4660 datasheet(11/28 Pages) AD

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LTM4660

Rev. 0

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DECOUPLING REQUIREMENTS

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

CFLY

External Flying Capacitor Requirement, 30V ≤ VIN ≤ 60V, VOUT = 12V

POUT = 300W (Note 3)

100

120

μF

CMID

External Midpoint Capacitor Requirement, 30V ≤ VIN ≤ 60V, VOUT = 12V POUT = 300W (Note 3)

100

120

μF

COUT

External Output Capacitor Requirement, 30V ≤ VIN ≤ 60V, VOUT = 12V

POUT = 300W

100

μF

TA = 25°C. Refer to Block Diagram.

OPERATION

Module Description

LTM4660 is a high efficient Intermediate Bus

Converter (IBC) utilizing a hybrid switched capacitor

topology. Four power switches along with capacitor

bank CFLY and CMID form a switched capacitor stage,

dividing the input voltage by two at MID. Voltage at MID

is further stepped down through a power inductor and

output capacitor, similar to a step down switching con-

verter. LTM4660 employs peak current mode control of

the inductor current for pulse width modulation of the

switches and to maintain accurate output regulation. Soft

switching of the power switches results in excellent effi-

ciency and EMI performance.

Current mode control enables fast cycle-by-cycle current

limiting of the inductor current and hence protects the

internal components of LTM4660 during short-circuit

conditions. With current mode control, LTM4660 exhib-

its good transient performance and stability margins for

wide range of output capacitors. An internal compensa-

tion network included inside LTM4660 is sufficient for

most typical applications. The VFB pin is used to program

the output voltage with a single resistor to ground.

Switching frequency can be programmed by a single

resistor connected between FREQ pin and SGND. Typical

switching frequency for IBC applications with LTM4660 is

300kHz to 500kHz. A phase-locked loop inside the mod-

ule enables synchronizing the switching frequency to an

external clock.

Pulling the RUN pin below 1.1V forces the regulator into

a shutdown state by turning off all switching and internal

circuits. The TRACK/SS pin is used for programming the

output voltage ramp and voltage tracking during start-

up. Internal bandgap reference of 0.8V can be overridden

by applying a suitable voltage at EXT_REF pin. See the

Applications Information section.

A general purpose temperature diode is included to moni-

tor internal temperature of the module. In addition, TEMP

pin of the module is used to program the OTP trip point.

Internal overvoltage and undervoltage comparators pull

the open-drain PGOOD output low if the output feedback

voltage exits the regulation window.

Capacitor banks CFLY and CMID connected external to the

µModule, are also part of the energy transfer elements.

LTM4660 utilizes these capacitor-banks to efficiently

deliver energy from input to output. These capacitors

are initially precharged in the Capacitor Balancing phase

using proprietary control techniques. This balancing elim-

inates large transient currents seen in similar switched

capacitor based topologies. Voltages of capacitor banks

are continuously monitored and balanced by LTM4660.

Dedicated pins TIMER and HYS_PRGM are provided to set

the balancing time interval and voltage window and can

be adjusted for each application of LTM4660. Following

balancing phase, regular switching action begins. During

each switching cycle, capacitor CFLY is connected either

in series with or in parallel to CMID. See Operation and

Applications Information section.

Capacitor Balancing Phase

During initial power up, voltage across the flying capacitor

(CFLY) and CMID are measured. If either of these voltages

are not at VIN/2, the TIMER’s capacitor will be allowed to

charge up. When the TIMER capacitor’s voltage reaches

0.5V, internal current sources to bring CFLY voltage to

VIN/2 are turned ON. After the CFLY voltage has reached

VIN/2, CMID will then be charged to VIN/2. The TRACK/SS

pin is pulled low during this duration. The FAULT pin will

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