Datasheet

LTC2974
31
2974fc
For more information www.linear.com/LTC2974
OPERATION Data Contents (On_off_config_use_pmbus=0)
On or Off
SYMBOL Action Operation_control[1:0] Operation_margin[1:0] Operation_fault[1:0] Reserved (read only)
BITS b[7:6] b[5:4] b[3:2] b[1:0]
FUNCTION
Output at nominal 00, 01 or 10 00 XX 00
Margin low (ignore faults and
warnings)
00, 01 or 10 01 01 00
Margin low 00, 01 or 10 01 10 00
Margin high (ignore faults and
warnings
00, 01 or 10 10 01 00
Margin high 00, 01 or 10 10 10 00
Reserved All remaining combinations
ON_OFF_CONFIG
The ON_OFF_CONFIG command configures the combination of CONTROL pin input and PMBus commands needed
to turn the LTC2974 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 tUPDATE_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
BIT(S) SYMBOL OPERATION
b[7:5] Reserved Don’t care. Always returns 0.
b[4] On_off_config_controlled_on Control default autonomous power up operation.
0: Unit powers up regardless of the CONTROL 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 CONTROL 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].
1: Unit responds to Operation_control[1:0]. Depending on On_off_config_use_control, the unit may also
require the CONTROL pin to be asserted for the unit to start.
b[2] On_off_config_use_control Controls how unit responds to the CONTROL pin.
0: Unit ignores the CONTROL pin.
1: Unit requires the CONTROL 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 CONTROL 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. The device does not sink current in
order to decrease the output voltage fall time.
pMbus coMManD DescripTion