LTM8045 datasheet(17/54 Pages) AD

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LTM4655

Rev. 0

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PGDFB1 (D2): Channel 1 Power Good Feedback

Programming Pin. Connect PGDFB1 to VOSNS1+ through a

resistor, RPGDFB1. RPGDFB1 configures the voltage thresh-

old of (VOUT1+ – VOUT1–) for which PGOOD1 toggles its

state. If the PGOOD1 feature is used, set RPGDFB1 to:

RPGDFB1 =

VOUT1+ – VOUT1–

0.6V

– 1 • 4.99k

(1)

Otherwise, leave PGDFB1 open circuit.

A small filter capacitor (220pF) internal to the LTM4655

on this pin provides high frequency noise immunity for

the PGOOD1 output indicator.

PGDFB2 (D7): Channel 2 Power Good Feedback

Programming Pin. Connect PGDFB2 to VOSNS2+ through a

resistor, RPGDFB2. RPGDFB2 configures the voltage thresh-

old of (VOUT2+ – VOUT2–) for which PGOOD2 toggles its

state. If the PGOOD2 feature is used, set RPGDFB2 accord-

ing to Equation 2.

RPGDFB2 =

VOUT2+ – VOUT2–

0.6V

– 1

⎡

⎣

⎢

⎤

⎦

⎥

• 4.99k

(2)

Otherwise, leave PGDFB2 open circuit.

A small filter capacitor (220pF) internal to the LTM4655

on this pin provides high frequency noise immunity for

the PGOOD2 output indicator.

fSET1 (E3): Channel 1 Oscillator Frequency Programming

Pin. The default switching frequency of channel 1 is

400kHz. If needed, the programmed frequency can be

increased by connecting a resistor between fSET1 and

SVOUT1–. Keep fSET1-related trace lengths short. (See the

Applications Information section.) Note the synchroniza-

tion range of CLKIN1 is approximately ±40% of the oscil-

lator frequency programmed by this fSET1 pin.

fSET2 (E8): Channel 2 Oscillator Frequency Programming

Pin. The default switching frequency of channel 2 is

400kHz. If needed, the programmed frequency can be

increased by connecting a resistor between fSET2 and

SVOUT2–. Keep fSET2-related trace lengths short. (See the

Applications Information section.) Note the synchroniza-

tion range of CLKIN2 is approximately ±40% of the oscil-

lator frequency programmed by this fSET2 pin.

CLKIN1 (B1): Channel 1 Mode Select and Oscillator

Synchronization Input. Referred to GND. Leave CLKIN1

open circuit for forced continuous mode operation.

Alternatively, this pin can be driven so as to synchronize

the switching frequency of channel 1 to a clock signal.

In this condition, channel 1 operates in forced continu-

ous mode and the cycle-by-cycle turn-on of its primary

MOSFET is coincident with the rising edge of the clock

applied to CLKIN1. Note the synchronization range of

CLKIN1 is approximately ±40% of the oscillator frequency

programmed by the fSET1 pin. (See the Applications

Information section.) The LTM4655 contains a built-in

dual 180° out-of-phase clock generator. Electrically con-

nect CLKIN1 to CLKOUT1 with a short trace, if desired,

to synchronize the switching frequency of channel 1

to CLKOUT1. If 0° phase interleaving is desired, connect

CLKOUT1 to both CLKIN1 and CLKIN2.

CLKIN2 (B6): Channel 2 Mode Select and Oscillator

Synchronization Input. Referred to GND. Leave CLKIN2

open circuit for forced continuous mode operation.

Alternatively, this pin can be driven so as to synchronize

the switching frequency of channel 2 to a clock signal. In

this condition, channel 2 operates in forced continuous

mode and the cycle-by-cycle turn-on of its primary

MOSFET is coincident with the rising edge of the clock

applied to CLKIN2. Note the synchronization range of

CLKIN2 is approximately ±40% of the oscillator frequency

programmed by the fSET2 pin. (See the Applications

Information section.) The LTM4655 contains a built-in

dual 180° out-of-phase clock generator. Electrically

connect CLKIN2 to CLKOUT2 with a short trace, if desired,

to synchronize the switching frequency of channel 2

to CLKOUT2. If 0° phase interleaving is desired, connect

CLKOUT1 to both CLKIN1 and CLKIN2.

PIN FUNCTIONS

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