LTM4637 datasheet(8/32 Pages) LINER

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LTM4633

4633f

For more information www.linear.com/LTM4633

pin FuncTions

FREQ/PLLLPF(L8):FrequencySetandPLLLowpassFilter

Pin. This pin is driven with a DC voltage to set the operating

frequency. Generally the pin is just connected to INTVCC to

set the typical 750kHz operating frequency. Applying a DC

voltage of 1.4V to this pin will set the frequency to 600kHz

and 1.6V will set it to 700kHz. When an external clock is

used, then the FREQ/PLLLPF pin must not be connected

to any DC voltage. The pin must be floating and will have

the proper internal compensation for the internal loop

filter. For VOUT1,2,3 ≤ 1.5V use 600kHz, and for VOUT1,2,3

≥ 1.5V use ≥700kHz. These frequecny settings optimize

efficiency and eliminate minimum on-time issues for less

than 1V output. See the Applications Information section.

MODE/PLLIN (L9): Force Continuous Mode, Burst Mode,

or Pulse-Skipping Mode Selection Pin and External Syn-

chronization Input to Phase Detector Pin. Connect this pin

to SGND to force all channels into the continuous mode

of operation. Connect to INTVCC to enable pulse-skipping

modeofoperation.LeavingthepinfloatingwillenableBurst

Mode operation. A clock on the pin will force the controller

into continuous mode of operation and synchronize the

internal oscillator.

RUN1,RUN2,RUN3(L10,L11,K11):RunControlInputs.A

voltage above 1.3V on any RUN pin turns on that particular

channel. However, forcing any of these RUN pins below

1.2V causes that channel to shut down. Each of the RUN

pins has an internal 10k resistor to ground. This resistor

can be used with an external pull-up resistor to the input

voltage to set a UVLO for that channel, or simply to turn

on the channel. The RUN pins have a maximum voltage

of 6V. See the Applications Information section.

PGOOD12, PGOOD3 (M2, M3): Output voltage power

good indicator for VOUT1 and VOUT2 are combined, and

VOUT3 separate. The open-drain logic output is pulled to

ground when the output voltage is not within ±7.5% of the

regulation point.

COMP1, COMP2, COMP3 (M4, L4, K4): Current Control

Threshold and Error Amplifier Compensation Point. The

current comparator threshold increases with this control

voltage. The LTM4633 regulator channels are all internally

compensated for proper stability. COMP1 and COMP2 can

be tied together for PolyPhase® 20A parallel operation.

See the Applications Information section.

VFB1, VFB2, VFB3 (M5, L5, K5): The Negative Input of the

Error Amplifier for Each of the Three Channels. Internally,

each of these pins is connected to their respective output

with a 60.4k precision resistor. Different output voltages

can be programmed with an additional resistor between

eachindividualVFBpinandground.InPolyPhaseoperation,

tying the VFB1 and VFB2 pins together allows for parallel

operation up to 20A. See the Applications Information

section for details.

TK/SS1,TK/SS2,TK/SS3(M9,M10,M11):OutputVoltage

TrackingandSoft-StartInputs.Whenoneparticularchannel

is configured to be the master, a capacitor to ground at

this pin sets the ramp rate for the master channel’s output

voltage. When the channel is configured to be the slave,

the VFB voltage of the master channel is reproduced by a

resistor divider and applied to this pin. Internal soft-start

currents of 1.5μA are charging the soft-start capacitors.

In dual output (2 + 1) mode, TK/SS1 and TK/SS2 need to

be shorted externally.

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