LTM4680 datasheet(17/132 Pages) AD

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LTM4681

Rev. 0

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PIN FUNCTIONS

SGND01, SGND23 (F10-F11, U10-U11): SGND is the sig-

nal ground return path of the LTM4681 internal control-

lers. SGND is not internally connected to GND. Connect

SGND to GND local to the LTM4681. See recommended

layout.

VIN01 (A5-A6, B5-B6, C5-C6, D5-D6, E5-E6, F5-F6,

G5-G6, H5-H6, J5-J6, K5-K6): Positive Power Input to

Channel 0 and 1 Switching Stages. Provide sufficient

decoupling capacitance in the form of multilayer ceramic

capacitors (MLCCs) and low ESR electrolytic (or equiv-

alent) to handle reflected input current ripple from the

step-down switching stage. MLCCs should be placed as

close to the LTM4681 as physically possible. See Layout

Recommendations in the Applications Information

section.

VIN23 (N5-N6, P5-P6, R5-R6, T5-T6, U5-U6, V5-V6,

W5-W6, Y5-Y6, AA5-AA6, AB5-AB6): Positive Power

Input to Channel 2 and 3 Switching Stages. Provide suf-

ficient decoupling capacitance in the form of MLCCs and

low ESR electrolytic (or equivalent) to handle reflected

input current ripple from the step-down switching stage.

MLCCs should be placed as close to the LTM4681 as

physically possible. See Layout Recommendations in the

Applications Information section.

SW0 (C1-C2, D1-D2, E1-E2): Switching Node of Channel

0 Step-Down Converter Stage. Used for test purposes

or EMI-snubbing. May be routed a short distance to a

local test point to monitor switching action of channel

0, if desired, but do not route near any sensitive signals;

otherwise, leave electrically isolated (open).

SW1 (G1-G2, H1-H2, J1-J2): Switching Node of Channel

1 Step-Down Converter Stage. Used for test purposes

or EMI-snubbing. May be routed a short distance to a

local test point to monitor switching action of channel

1, if desired, but do not route near any sensitive signals;

otherwise, leave open.

SW2 (P1-P2, R1-R2, T1-T2): Switching Node of Channel

2 Step-Down Converter Stage. Used for test purposes

or EMI-snubbing. May be routed a short distance to a

local test point to monitor switching action of channel

2, if desired, but do not route near any sensitive signals;

otherwise, leave open.

SW3 (V1-V2, W1-W2, Y1-Y2): Switching Node of Channel

3 Step-Down Converter Stage. Used for test purposes or

EMI-snubbing. May be routed a short distance to a local

test point to monitor switching action of channel 3, if

desired, but do not route near any sensitive signals; oth-

erwise, leave open.

SVIN_01 (J8): Input Supply for LTM4681’s Internal Control

IC for channel 0 and 1. In most applications, SVIN_01 con-

nects to VIN01. SVIN_01 can be operated from an auxiliary

supply separate from VIN01 for powering the VIN01 from

a lower supply like 3.3V. The SVIN_01 pin has an onboard

1Ω and 1µF decoupling capacitor. The 1Ω resistor is used

to measure the actual control chip current. See MFR_

READ_ICHIP and MFR_ADC_CONTROL COMMAND sec-

tion. When operating from 4.5V to 5.75V with no auxiliary

bias supply, then the main input supply should connect to

SVIN_01 and INTVCC_01. See Test Circuit 2 for an example.

In this configuration, the ICHIP current will not be relevant

since INTVCC_01 is connected to SVIN_01.

SVIN_23 (P11): Input Supply for LTM4681’s Internal

Control IC for channel 2 and 3. In most applications,

SVIN_23 connects to VIN_23. SVIN_23 can be operated from

an auxiliary supply separate from VIN23 for powering the

VIN23 from a lower supply like 3.3V. The SVIN_23 pin has

an onboard 1Ω and 1µF decoupling capacitor. The 1Ω

resistor is used to measure the actual control chip cur-

rent. See MFR_READ_ICHIP and MFR_ADC_CONTROL

COMMAND section. When operating from 4.5V to 5.75V

with no auxiliary bias supply, then the main input sup-

ply should connect to SVIN_23 and INTVCC_23. See Test

Circuit 2 for an example. In this configuration, the ICHIP

current will not be relevant since INTVCC_23 is connected

to SVIN_23.

VIN_VBIAS (N9): Input pin to the internal step down regula-

tor that produces 5.5V (VBIAS pin) to power both internal

controllers to reduce power dissipation after power up.

Each internal controller has an INTVCC_01 or INTVCC_23

regulator that is powered from SVIN_01 or SVIN_23. To

eliminate this power loss through these linear regulators,

the VBIAS powers both at very high efficiency.

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