LTM4652 datasheet(21/38 Pages) AD

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LTM4652

Rev. 0

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APPLICATIONS INFORMATION

Figure 10. Output Coincident Tracking Waveform

TIME

MASTER OUTPUT

SLAVE OUTPUT

4652 F10

For example, RTR(TOP) = 60.4k and RTR(BOT) = 13.3k is a

good combination for coincident tracking for a VOUT(MA)

= 1.5V and VOUT(SL) = 3.3V application.

Power Good

The PGOOD pins are open drain pins that can be used to

monitor valid output voltage regulation. This pin monitors

a 10% window around the regulation point. A resistor can

be pulled up to a particular supply voltage no greater than

6V maximum for monitoring.

Stability Compensation

The LTM4652 has a built-in 10pF high frequency filter

capacitor from COMP to SGND on each output chan-

nel. An external R-C filtering circuit is required to add

from COMP to SGND to achieve fast Type II control loop

compensation. Table 6 is provided for most applica-

tion requirements. The Analog Devices µModule Power

Design Tool (LTpowerCAD) provides for other control loop

optimization.

Run Enable

The RUN pins have an enable threshold of 1.4V maximum,

typically 1.22V with 135mV of hysteresis. They control the

turn on of each of the channels and INTVCC. These pins

can be pulled up to VIN for 5V operation, or a 5V Zener

diode can be placed on the pins and a 10k to 100k resis-

tor can be placed up to higher than 5V input for enabling

the channels. There is 1µA pull-up current for each RUN

pin. The LTM4652 will turn on with RUN floating. Please

note RUN has a 6V Abs Max voltage rating. The RUN

pins can also be used for output voltage sequencing.

In parallel operation the RUN pins can be tied together

and controlled from a single control. See the Typical

Applications circuits in Figure 31.

INTVCC and EXTVCC

The LTM4652 module has an internal 5V low dropout

regulator that is derived from the input voltage. This reg-

ulator is used to power the control circuitry and the power

MOSFET drivers. This regulator can source up to 50mA,

and typically uses ~30mA for powering the device at the

maximum frequency. This internal 5V supply is enabled

by either RUN1 or RUN2.

EXTVCC allows an external 5V supply to power the

LTM4652 and reduce power dissipation from the internal

low dropout 5V regulator. The power loss savings can be

calculated using Equation 10.

(VIN – 5V) • 30mA = PLOSS

(10)

EXTVCC has a threshold of 4.7V for activation, and a max-

imum rating of 6V. When using a 5V input, connect this

5V input to EXTVCC also to maintain a 5V gate drive level.

EXTVCC must sequence on after VIN, and EXTVCC must

sequence off before VIN.

Differential Remote Sense Amplifier

An accurate differential remote sense amplifier is provided

to sense low output voltages accurately at the remote

load points. This is especially true for high current loads.

The amplifier can be used on one of the two channels, or

on a single parallel output. It is very important that the

DIFFP and DIFFN are connected properly at the output,

and DIFFOUT is connected to either VOUTS1 or VOUTS2.

In parallel operation, the DIFFP and DIFFN are connected

properly at the output, and DIFFOUT is connected to

one of the VOUTS pins. Review the parallel schematics in

Figure 32 and Figure 34 and review Figure 4. Please note

the differential amplifier can be used for ≤3.3V outputs.

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