LTM4657 datasheet(6/28 Pages) AD

6 / 28 page

LTM4657

Rev. A

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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): Switching Frequency Program Pin. Frequency

is set internally to 500kHz. 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 con-

nected to VOSNS+ with a 60.4kΩ precision resistor. Output

voltages 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 GND 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

0.5V on this pin bypasses the internal reference input

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

TRACK voltage. Above 0.5V, the tracking function stops

and the internal reference resumes control of the error

amplifier. There’s an internal 6µA pull-up current from

INTVCC on this pin, so putting a capacitor here provides

soft-start function. See the Applications Information sec-

tion for details.

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

External Synchronization Input to Phase Detector. Tie

MODE/CLKIN to GND for discontinuous mode of opera-

tion. Floating MODE/CLKIN or tying it to a voltage above

1V will select forced continuous mode. Furthermore, con-

necting 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

Operation. 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.

PACKAGE ROW AND COLUMN LABELING MAY VARY

AMONG µModule PRODUCTS. REVIEW EACH PACKAGE

LAYOUT CAREFULLY.

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