LTC2970-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2970-1' PDF : 36 Pages View PDF
LTC2970/LTC2970-1
U
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.
22
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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