LTC2978A View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC2978A

8-Channel PMBus Power System Manager Featuring Accurate Output Voltage Measurement

Linear Technology 

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LTC2978A

PMBus Command Description

ON_OFF_CONFIG

The ON_OFF_CONFIG command configures the combination of CONTROLn pin input and PMBus bus commands needed

to turn the LTC2978A 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 VIN is initially

applied, the part will typically require tINIT 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 tOFF_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

b[7:5] Reserved

b[4] On_off_config_controlled_on

b[3] On_off_config_use_pmbus

b[2] On_off_config_use_control

b[1] Reserved

b[0] On_off_config_control_fast_off

OPERATION

Don’t care. Always returns 0.

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.

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.

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.

Not supported. Always returns 1.

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 VOUT_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 register does not respond to the global page command (PAGE=0xFF).

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For more information www.linear.com/LTC2978A

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