LTC7151S datasheet(17/38 Pages) AD

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LT7182S

Rev. 0

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OPERATION

LT7182S initialization typically requires 13ms. If CFG pins

are disabled (MFR_CONFIG_ALL_LT7182S bit 6 set to 1

in EEPROM), the initialization time is reduced to 10ms

(typical).

After initialization is complete, comparators monitor PVIN0

and PVIN1. The PVIN voltage must exceed the channel’s

programmable VIN_ON threshold for the channel to oper-

ate. By default, SHARE_CLK will be held low until PVIN0

exceeds VIN_ON for PAGE 0, or if PVIN0 falls below VIN_OFF.

By default, PVIN1 does not affect SHARE_CLK. The default

behavior for both channels is to turn off and remain off

if SHARE_CLK is low. See the MFR_CHAN_CONFIG_

LT7182S command in the LT7182S PMBus/I2C Reference

Manual for information on how to configure this behavior.

The RUN pin pull-down current (1.5mA typical) is released

by the LT7182S after the device completes POR initializa-

tion and the first time the channel’s PVIN potential exceeds

the VIN_ON threshold.

SOFT-START

When all conditions required for startup have been met,

and a channel is enabled, the LT7182S waits for the com-

manded turn-on delay and ramps the target output voltage

up to the commanded voltage set-point. The soft-start rise

time is set by the TON_RISE command, default 1ms. The

turn-on delay is set by TON_DELAY, which is 0ms by fac-

tory default. The LT7182S PWM always uses pulse-skip

mode during soft-start, which allows the regulator to start

up into a pre-biased load. If forced continuous conduc-

tion mode is selected (MFR_PWM_MODE_LT7182S bit

0 cleared to 0), the channel will transition to continuous

conduction mode after the commanded voltage set-point

is reached.

SHUTDOWN

The LT7182S can be programmed to turn off immediately

or to sequence off.

When sequencing off, the LT7182S waits for the turn-off

delay then performs a soft-stop ramp in which the regu-

lation target voltage is ramped down to zero. The turn-off

delay is set by the TOFF_DELAY command, default zero.

The target voltage ramp-down time is set by TOFF_FALL,

default 2ms. By default, the channel will ramp down in

forced continuous conduction mode. The ramp-off behav-

ior can be configured using MFR_PWM_MODE_LT7182S.

Sequencing off occurs if OPERATION is set to 0x40, or if

the RUN pin is de-asserted and ON_OFF_CONFIG bit 0 is

set to 0 and bit 2 is set to 1.

When immediate turn-off occurs, the regulator ramps

the inductor current to zero as quickly as possible and

then stops switching. In this case, the output voltage will

decay based only on the load current and the optional

internal 250Ω pull-down. The internal 250Ω pull-down

can be disabled by clearing bit 6 of MFR_CHAN_CONFIG_

LT7182S. Immediate shutdown occurs in any the follow-

ing situations:

• PVIN falls below the VIN_OFF threshold

• If the OPERATION command is cleared to 0x00, if

ON_OFF_CONFIG bit 3 is set to 1

• A fault condition occurs which causes the output to

turn off

• The RUN pin is de-asserted and ON_OFF_CONFIG

has been configured such that RUN pin de-assertion

causes immediate shutdown (ON_OFF_CONFIG bits 0

and 2 both set to 1)

• The FAULT pin for the channel is pulled low externally,

unless MFR_FAULT_RESPONSE has been cleared to

0x00.

• Loss of SHARE_CLK, unless bit 2 of MFR_CHAN_

CONFIG_LT7182S has been cleared

WARNING AND FAULT HANDLING

The LT7182S continuously monitors the system for fault

and warning conditions.

Fault responses are configurable using the correspond-

ing FAULT_RESPONSE commands, such as VOUT_UV_

FAULT_RESPONSE, VOUT_OV_FAULT_RESPONSE, etc.

Possible fault responses are as follows:

• Continue Operation (Ignore)

• Shut down immediately and retry if fault condition is

no longer present

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