LTM4643 datasheet(9/24 Pages) AD

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LTM4710-1

Rev. 0

For more information www.analog.com

OPERATION

The LTM4710-1 is a quad output step-down switch

mode DC/DC power supply. It integrates four separate

regulators, each capable of delivering up to 8A contin-

uous output current with few external input and output

capacitors. Each regulator provides precisely regulated

output voltage programmable from 0.5V to 3.6V over a

2.5V to 5.5V input voltage range. See typical application

schematic (Figure 1).

The LTM4710-1 integrates four separate constant-fre-

quency peak current mode control regulators, power

MOSFETs, inductors, and other supporting discrete

components. It employs Silent Switcher 2 technology,

which allows fast switching edges for high efficiency at

high switching frequencies, while simultaneously achiev-

ing good EMI performance. Ceramic Capacitors on VIN

keep all the fast AC current loops small, improving

EMI performance.

With current mode control and internal feedback loop com-

pensation, the LTM4710-1 has sufficient stability margins

and fast transient performance with a wide range of out-

put capacitors, even with all ceramic output capacitors.

The switching frequency for LTM4710-1 can be adjusted

by an external resistor from RT to AGND, or the

LTM4710-1 can be externally synchronized to a clock.

See the Applications Information section.

Current mode control provides cycle-by-cycle fast current

limiting. Peak current limiting is provided in an overcur-

rent condition. The internal overvoltage and undervolt-

age comparators pull the open-drain PG output low if the

output feedback voltage exits a –2% and +10% window

around the regulation point. Furthermore, in an overvolt-

age condition, the internal top MOSFET is turned off, and

the bottom MOSFET is turned on and held on until the

overvoltage condition clears.

The multiphase operation can be easily configurable with

synchronization and phase mode controls.

Pulling the RUN pin to GND forces the controller into its

shutdown state, turning off both power MOSFETs and

most of the internal control circuitry.

The SSTT pin is used for power supply tracking, soft-start

programming and, and monitoring die temperature. See

the Applications Information section.

Forced continuous mode (FCM) is the only opera-

tion mode recommended for low ripple and low noise

consideration. The switching frequency of the four

channels should always be synchronized regardless the

output(s) are paralleled or independent. For multiphase

paralleled output, phase-shift interleaving is recom-

mended. For independent outputs, an aligned main-switch

turn-on transition is recommended. See the Applications

Information section and Typical Applications for more

information.

The typical LTM4710-1 application circuit is shown in

Figure 1. External component selection is primarily deter-

mined by the input voltage, the output voltage and the

maximum load current. See Table 10 for specific external

capacitor requirements for a particular application.

VIN to VOUT Step-Down Ratios

There are restrictions in the minimum VOUT step-down

ratio that can be achieved for a given input voltage due to

the minimum on-time limits of the regulator.

APPLICATIONS INFORMATION

The minimum on-time limit imposes a minimum duty cycle

of the converter, which can be calculated with Equation 1.

D(MIN) = tON(MIN) • fSW

(1)

where tON(MIN) is the minimum on-time, 40ns typical

for LTM4710-1. In the rare cases where the minimum

duty cycle is surpassed, the output voltage will remain in

regulation, but the switching frequency will decrease from

its programmed value.

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