LTM4622 datasheet(9/28 Pages) LINER

9 / 28 page

LTM4622

Rev F

For more information www.analog.com

OPERATION

APPLICATIONS INFORMATION

The LTM4622 is a dual output standalone non-isolated

switch mode DC/DC power supply. It can deliver two 2.5A

DC, 3A peak output current with few external input and

output ceramic capacitors. This module provides dual

precisely regulated output voltage programmable via

two external resistor from 0.6V to 5.5V over 3.6V to 20V

input voltage range. With INTVCC tied to VIN, this module

is able to operate from 3.3V input. The typical application

schematic is shown in Figure 24.

The LTM4622 contains an integrated controlled on-time

valley current mode regulator, power MOSFETs, inductor,

and other supporting discrete components. The default

switching frequency is 1MHz. For output voltages between

2.5V and 5.5V, an external resistor is required between

FREQ and GND pins to set the operating frequency to

higher frequency to optimize inductor current ripple.

For switching noise-sensitive applications, the switch-

ing frequency can be adjusted by external resistors and

the μModule regulator can be externally synchronized

to a clock within ±30% of the set frequency. See the

Applications Information section.

With current mode control and internal feedback loop

compensation, the LTM4622 module has sufficient

stability margins and good transient performance with

a wide range of output capacitors, even with all ceramic

output capacitors.

Current mode control provides cycle-by-cycle fast cur-

rent limiting. An internal overvoltage and undervoltage

comparators pull the open-drain PGOOD output low if

the output feedback voltage exits a ±8% window around

the regulation point. Furthermore, an input overvoltage

protection been utilized by shutting down both power

MOSFETs when VIN rises above 22.5V to protect internal

devices.

Multiphase operation can be easily employed by connect-

ing SYNC pin to an external oscillator. Up to 6 phases can

be paralleled to run simultaneously a good current sharing

guaranteed by current mode control loop.

Pulling the RUN pin below 1V forces the controller into

its shutdown state, turning off both power MOSFETs and

most of the internal control circuitry. At light load cur-

rents, Burst Mode operation can be enabled to achieve

higher efficiency compared to continuous mode (CCM) by

setting MODE pin to INTVCC. The TRACK/SS pin is used

for power supply tracking and soft-start programming.

See the Applications Information section.

The typical LTM4622 application circuit is shown in

Figure 24. External component selection is primarily deter-

mined by the input voltage, the output voltage and the

maximum load current. Refer to Table 7 for specific exter-

nal capacitor requirements for a particular application.

VIN to VOUT Step-Down Ratios

There are restrictions in the maximum VIN and VOUT step

down ratio that can be achieved for a given input voltage

due to the minimum off-time and minimum on-time limits

of the regulator. The minimum off-time limit imposes a

maximum duty cycle which can be calculated as

DMAX = 1 – tOFF(MIN) • fSW

where tOFF(MIN) is the minimum off-time, 45ns typical for

LTM4622, and fSW is the switching frequency. Conversely

the minimum on-time limit imposes a minimum duty

cycle of the converter which can be calculated as

DMIN = tON(MIN) • fSW

where tON(MIN) is the minimum on-time, 20ns typical for

LTM4622. In the rare cases where the minimum duty

cycle is surpassed, the output voltage will still remain

in regulation, but the switching frequency will decrease

from its programmed value. Note that additional thermal

derating may be applied. See the Thermal Considerations

and Output Current Derating section in this data sheet.

LTM4622 Datasheet(PDF) 9 Page - Linear Technology

LTM4622 Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL