LTC2970CUFD datasheet(22/36 Pages) LINER

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LTC2970/LTC2970-1

29701fc

OPERATIO

This causes open-drain outputs GPIO_1 and GPIO_0 to

automatically pull the power supplies’ run/soft-start pins

to ground.

CHn_A_IDAC(): Hard connect Chn_a_idac[7:0] with a value

that forces the power supplies off when GPIO_CFG = 1.

Verify that Chn_a_idac_pol is at the appropriate value.

CHn_A_IDAC_TRACK(): Set Chn_a_idac_track_en = 1,

and set the Chn_a_idac_track[7:0] target value to the

code that causes VOUTn to most closely approximate the

corresponding power supply’s feedback node voltage

when it is in regulation.

CHn_A_DELAY_TRACK(): Set the value by which the

incrementing of IDACn should be delayed with respect to

the start of tracking event. This controls whether the power

supplies track up coincidentally or sequentially.

IO(): Release the run/soft-start pins by programming

io_gpio_n = 1. This will enable the power supplies without

allowing their outputs to move since these are held low

by Chn_a_idac[7:0]. Wait until power supplies have had

sufﬁcient time to start running before starting tracking.

SYNC(): Optional command that allows multiple LTC2970-

1’s to be synchronized for tracking. Writing Sync_track

= 1 will allow the LTC2970-1 to ﬁnish its current ADC

conversion before having it wait to receive io_track_start

= 1. The LTC2970-1 will timeout this wait command after

tTIMEOUT_SYNC. Reading back Sync_track = 1 using the

global address will ensure all LTC2970-1’s are synchronized

before proceeding with the tracking operation.

IO(): Set Io_track_start = 1 and keep the run/soft-start pins

enabled. Use the global I2C address to simultaneously track

up power supplies across multiple LTC2970-1’s.

LTC2970-1 response: For each tracking enabled channel,

the LTC2970-1 will decrement the CHn_A_delay_track

counter at a rate of tDEC_TRACK. As soon as a channel’s

tracking counter reaches zero, the LTC2970-1 will begin

stepping the value of Chn_a_idac[7:0] by one count until

the ﬁnal value of Chn_a_idac_track[7:0] is reached, at which

point Chn_a_idac_track_en is de-asserted. When the ﬁnal

value is reached for all channels, GPIO_CFG is asserted

low. After a time delay of tHOLD_TRACK, Chn_a_idac_en is

de-asserted.

Power-Up Tracking Rules:

Tracking cannot begin if Chn_a_idac_con is not connected.

This condition is met when the previous procedure is

followed.

Chn_a_idac_track_pol, Chn_a_idac_track_en, and ch0_

idac[7:0] updates will be ignored after IO(Io_track_start)

is asserted until tracking is complete or whenever tracking

is pending, i.e., GPIO_CFG pulled high with either GPIO_0

or GPIO_1 asserted pulled high.

11. Tracking Power Supplies Off (LTC2970-1 Only)

The LTC2970-1 tracking feature allows the I2C to initiate

a controlled power down of two or more supplies.

Procedure: This procedure describes all steps necessary

to track down two or more power supplies. Steps that

require I2C interaction are preﬁxed with the required I2C

command function.

CHn_IDAC(): Disable the IDAC’s for each tracking enabled

channel (Chn_a_idac_en = 0). Ensure Chn_a_idac_pol is

at the appropriate value.

CHn_IDAC_TRACK(): Select the channels to be tracked

by setting Chn_a_idac_track_en = 1, and set the target

value for each Chn_a_idac_track[7:0] to that which forces

the supply off.

CHn_A_DELAY_TRACK(): Set the value by which the

decrementing of that channel’s DAC should be delayed

with respect to the start of the tracking event. This con-

trols whether the supplies track down coincidentally or

sequentially.

SYNC(): Optional command that allows multiple LTC2970-

1’s to be synchronized for tracking. Writing Sync_track

= 1 will allow the LTC2970-1 to ﬁnish its current ADC

conversion before having it wait to receive io_track_start

= 1. The LTC2970-1 will timeout this wait command after

tTIMEOUT_SYNC. Reading back Sync_track = 1 using the

global address will ensure all LTC2970’s are synchronized

before proceeding with the tracking operation.

IO(): Set Io_track_start = 1. Use the global I2C address

to simultaneously track down power supplies across

multiple LTC2970’s.

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