LTM4643 datasheet(7/30 Pages) AD

7 / 30 page

LTM4638

Rev. C

For more information www.analog.com

PIN FUNCTIONS

VOUT (A1-A5, F3, G1-G3): Power Output Pins of the

Switching Mode Regulator. Apply output load between

these pins and GND pins. Recommend placing output

decoupling capacitance directly between these pins and

GND pins. See the Applications Information section for

paralleling outputs.

COMPb (F1): Internal Loop Compensation Network.

Connect to COMPa to use the internal compensation in

majority of applications.

FREQ(E1):SwitchingFrequencyProgramPin.Frequencyis

set internally to 600kHz. An external resistor can be placed

from this pin to GND to increase frequency, or from this

pin to INTVCC to reduce frequency. See the Applications

Information section for frequency adjustment.

COMPa (D1): Current control threshold and error ampli-

fier compensation point of the switching mode regulator

channel. The internal current comparator threshold is

linearly proportional to this voltage. Tie the COMPa pins

from different channels together for parallel operation.

The device is internal compensated. Connect to COMPb

to use the internal compensation. Or connect to a Type-II

C-R-C network to use customized compensation.

FB (C1): The Negative Input of the Error Amplifier for the

switching mode regulator. This pin is internally connected

toVOSNS+witha60.4kΩprecisionresistor.Outputvoltages

can be programmed with an additional resistor between

FB and VOSNS– pins. In PolyPhase® operation, tying the

FB pins together allows for parallel operation. See the

Applications Information section for details.

VOSNS+ (B1): Positive Input to the Differential Remote

Sense Amplifier. Internally, this pin is connected to FB

with a 60.4k 0.5% precision resistor. See the Applications

Information section for details.

PHMODE (G5): Control Input to the Phase Selector of the

Switching Mode Regulator. Determines the phase rela-

tionship between internal oscillator and CLKOUT. Tie it to

INTVCC for 2-phase operation, tie it to SGND for 3-phase

operation, and tie it to INTVCC/2 for 4-phase operation.

See Application Information section for details.

TRACK/SS (E2): Output Tracking and Soft-Start Pin of the

Switching Mode Regulator. Allows the user to control the

rise time of the output voltage. Putting a voltage below

0.6Vonthispinbypassestheinternalreferenceinputtothe

error amplifier, instead it servos the FB pin to the TRACK

voltage. Above 0.6V, the tracking function stops and the

internal reference resumes control of the error amplifier.

There’saninternal6µApull-upcurrentfromINTVCConthis

pin, so putting a capacitor here provides soft-start func-

tion. See the Applications Information section for details.

MODE/CLKIN (D2): Discontinuous Mode Select Pin and

External Synchronization Input to Phase Detector. Tie

MODE/CLKINtoGNDfordiscontinuousmodeofoperation.

Floating MODE/CLKIN or tying it to a voltage above 1V will

select forced continuous mode. Furthermore, connecting

MODE/CLKIN to an external clock will synchronize the

system clock to the external clock and puts the part in

forced continuous mode. See Applications Information

section for details.

VOSNS– (C2): Negative Input to the Differential Remote

Sense Amplifier. Connect an external resistor between FB

and VOSNS– pin to set the output voltage of the specific

channel. See the Applications Information section for

details.

CLKOUT (F2): Output Clock Signal for PolyPhase Op-

eration. The phase of CLKOUT with respect to CLKIN is

determined by the state of the respective PHMODE pin.

CLKOUT’s peak-to-peak amplitude is INTVCC to GND. See

Application Information section for details.

VIN (D3-D4, E3-E4, F4, G4): Power input pins connect to

the drain of the internal top MOSFET and signal VIN to the

internal 3.3V regulator for the control circuitry for each

switching mode regulator channel. Apply input voltages

between these pins and GND pins. Recommend placing

input decoupling capacitance directly between each of VIN

pins and GND pins.

INTVCC(B3):Internal3.3VRegulatorOutputoftheSwitch-

ing Mode Regulator Channel. The internal power drivers

and control circuits are powered from this voltage. The

LTM4638 has an internal 2.2µF decoupling capacitor. No

external decoupling capacitor is required.

PACKAGE ROW AND COLUMN LABELING MAY VARY

AMONG µModule PRODUCTS. REVIEW EACH PACKAGE

LAYOUT CAREFULLY.

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