Datasheet

LTC2977
34
2977fa
For more information www.linear.com/LTC2977
ON_OFF_CONFIG
The ON_OFF_CONFIG command configures the combination of CONTROLn pin input and PMBus bus commands needed
to turn the LTC2977 on/off, including the power-on behavior, as shown in the following table. This command register
responds to the global page command (PAGE=0xFF). After the part has initialized, an additional comparator monitors
VIN_SNS. The VIN_ON threshold must be exceeded before the output power sequencing can begin. After V
IN
is initially
applied, the part will typically require t
INIT
time to initialize and begin the TON_DELAY timer. The readback of voltages
and currents may require an additional wait for t
UPDATE_ADC
. A minimum t
OFF_MIN
wait time must be observed for any
CONTROL pin toggle used to turn the unit off and then back on.
ON_OFF_CONFIG Data Contents
BITS(S) SYMBOL OPERATION
b[7:5] Reserved Don’t care. Always returns 0.
b[4] On_off_config_controlled_on Controls default autonomous power-up operation.
0: Unit powers up regardless of the CONTROLn pin or OPERATION value. Unit always powers up with
sequencing. To turn unit on without sequencing, set TON_DELAY = 0.
1: Unit does not power up unless commanded by the CONTROLn pin and/or the OPERATION command
on the serial bus. If On_off_config[3:2] = 00, the unit never powers up.
b[3] On_off_config_use_pmbus Controls how the unit responds to commands received via the serial bus.
0: Unit ignores the Operation_control[1:0] bits.
1: Unit responds to Operation_control[1:0]. Depending on On_off_config_use_control, the unit may also
require the CONTROLn pin to be asserted for the unit to start.
b[2] On_off_config_use_control Controls how unit responds to the CONTROLn pin.
0: Unit ignores the CONTROLn pin.
1: Unit requires the CONTROLn pin to be asserted to start the unit. Depending on On_off_config_use_
pmbus the OPERATION command may also be required to instruct the device to start.
b[1] Reserved Not supported. Always returns 1.
b[0] On_off_config_control
_fast_off CONTROLn
pin turn off action when commanding the unit to turn off
0: Use the programmed TOFF_DELAY.
1: Turn off the output and stop transferring energy as quickly as possible, i.e. pull V
OUT_ENn
low
immediately. The device does not sink current in order to decrease the output voltage fall time.
CLEAR_FAULTS
The CLEAR_FAULTS command is used to clear any status bits that have been set. This command clears all fault and
warning bits in all unpaged status registers, and the paged status registers selected by the current PAGE setting. At
the same time, the device negates (clears, releases) its contribution to ALERTB.
The CLEAR_FAULTS command does not cause a unit that has latched off for a fault condition to restart. See Clearing
Latched Faults for more information.
If the fault condition is present after the fault status is cleared, the fault status bit shall be set again and the host noti
-
fied by the usual means.
Note: This command responds to the global page command (P
AGE=0xFF).
PMBus COMMAND DESCRIPTION