LTC2970CUFD datasheet(23/36 Pages) LINER

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LTC2970/LTC2970-1

29701fc

OPERATIO

LTC2970-1 response: Each tracking enabled channel is soft

connected. The GPIO_CFG pin is released allowing it to be

pulled high. The LTC2970-1 waits tSETUP_TRACK to allow

GPIO_CFG to settle. For each tracking enabled channel,

the Chn_a_delay_track counter is decremented 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. The tracking enable bit

is then cleared for both channels (Chn_a_idac_track_en

= 0).

IO(): The I2C interface may then be used to set GPIO_1

and GPIO_0 low, disabling the power supplies.

Power Down Tracking Rules:

Power down tracking requests will be ignored until the

user has disabled the IDAC’s by setting Chn_a_idac_en =

0 for each tracking enabled channel.

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 and whenever tracking

range is conﬁgured; (GPIO_CFG high with either GPIO_0

or GPIO_1 asserted high).

12. Continuous Power Supply Voltage Servo

The continuous voltage servo feature allows the LTC2970

to servo an external power supply to a programmed

value. The voltage of the external supply is monitored

over Chn_A_ADC and compared to a target value stored

in Chn_a_servo. After each conversion, Chn_A_IDAC is

incremented by 1, decremented by 1, or held; whichever

brings or keeps the measured voltage closer to the targeted

servo value.

Procedure:

Follow procedure for hard connecting or soft connecting

the LTC2970 to power supply trim pin; when updating

CHn_A_IDAC(), Chn_a_idac_servo_repeat should be as-

serted high. The servo channel’s IDAC must be enabled

before Chn_A_servo_en can be set high.

Determine the target servo voltage, Chn_a_servo[14:0].

Update CHn_A_SERVO() with Chn_a_servo_en = 1, and

Chn_a_servo[14:0].

Update CHn_A_IDAC() with Chn_a_idac_servo_repeat =

1. This step may be skipped if Chn_a_idac_servo_repeat

was set high during the soft or hard connect procedure.

LTC2970 response: The LTC2970 will continuously in-

crement, decrement or hold Chn_a_idac[7:0] in order

to match the measured value of (VINn_AP-VINn_AM) to

Chn_a_servo[14:0].

Whenever the CHn_A_SERVO() register is updated an in-

ternal ﬂag is cleared indicating that a successful servo has

not been completed. This internal ﬂag, Chn_a_servo_done,

initially causes the ADC to operate in an accelerated 12-bit

mode. Once the channel reaches the servo target, the ADC

switches back to 14-bit mode for two conversions before

asserting Chn_a_servo_done high.

In continuous voltage servo mode the Chn_a_servo_done

ﬂags allow the initial servo target to be reached quickly.

During this time, ADC conversions for all non-servo chan-

nels are temporarily inhibited.

Rules:

The IDAC associated with the servo channel must be

enabled. If Chn_a_idac_en is low the servo enable bit

Chn_a_servo_en is always forced low.

The IDAC associated with the servo channel must be con-

nected (Chn_a_idac_con = 1).

An IDAC fault may be generated during a continuous servo

operation. The LTC2970 will report the fault and continue

trying to servo that channel.

LTC2970-1 Only: There must be no pending tracking

commands. A pending tracking command will clear

Chn_a_servo_en.

LTC2970-1 Only: The tracking range must not be enabled;

(GPIO_CFG high with either GPIO_0 or GPIO_1 asserted

high). An enabled tracking range will clear Chn_a_servo_en

low.

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