Datasheet

LTC2977

2977fa

For more information www.linear.com/LTC2977

PMBus

COMMAND DESCRIPTION

MFR_DAC

This command register allows the user to directly program the 10-bit DAC. Manual DAC writes require the channel

to be in the ON state,TON_RISE to have expired and MFR_CONFIG_LTC2977 b[5:4] = 10b or 11b. Writing MFR_

CONFIG_LTC2977 b[5:4] = 10b commands the DAC to hard-connect with the value in Mfr_dac_direct_val. Writing

b[5:4] = 11b commands the DAC to soft-connect. Once the DAC has soft-connected, Mfr_dac_direct_val returns the

value that allowed the DAC to be connected without perturbing the power supply. MFR_DAC writes are ignored when

MFR_CONFIG_LT C 2977 b[5:4] = 00b or 01b.

MFR_DAC Data Contents

BIT(S) SYMBOL OPERATION

b[15:10] Reserved Read only, always returns 0.

b[9:0] Mfr_dac_direct_val DAC code value.

MFR_POWERGOOD_ASSERTION_DELAY

This command register allows the user to program the delay from when the internal power good signal becomes valid

until the power good output is asserted. This delay is counted using SHARE_CLK if available, otherwise the internal

oscillator is used. This delay is internally limited to 13.1 seconds, and rounded to the nearest 200µs. The read value

of this command always returns what was last written and does not reflect internal limiting.

The power good de-assertion delay and threshold source is controlled by Mfr_config_all_pwrgd_off_uses_uv.

Systems that require a fast power good de-assertion should set Mfr_config_all_pwrgd_off_uses_uv=1. This uses the

VOUT_UV_FAULT_LIMIT and the high speed comparator to de-assert the PWRGD pin. Systems that require a separate

power good off threshold should set Mfr_config_all_pwrgd_off_uses_uv=0. This uses the slower ADC polling loop

and POWER_GOOD_OFF to de-assert the PWRGD pin.

MFR_POWERGOOD_ASSERTION_DELAY Data Contents

BIT(S) SYMBOL OPERATION

b[15:0] Mfr_powergood_assertion_delay The data uses the L11 format.

This delay is counted using SHARE_CLK if available, otherwise the internal oscillator is used.

Delays are rounded to the nearest 200µs.

Units: ms. Max delay is 13.1 sec.