LTC2970CUFD datasheet(21/36 Pages) LINER

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LTC2970/LTC2970-1

29701fc

OPERATIO

soft connect failed with an IDAC fault (Fault_chn_a_idac =

1). Recall that a new hard connection requires the previous

value of Chn_a_idac_en = 0.

LTC2970-1 Only: Hard connect requests will be ignored

and the user will not be able to change Chn_a_idac_pol,

Chn_a_idac_con or Chn_a_idac[7:0] if GPIO_CFG is high

and either GPIO_0 or GPIO_1 are high.

LTC2970-1 Only: Hard connect requests will be ignored and

the user will not be able to change Chn_a_idac_pol, Chn_a_

idac_con or Chn_a_idac[7:0] if there is a pending tracking

operation.

7. Programming a Previously Connected IDAC

The LTC2970 IDAC’s may be programmed after they have

been connected with a soft connect or a hard connect

provided a servo operation is not enabled on the associ-

ated channel.

Procedure:

Determine the value for Chn_a_idac[7:0]. The values

‘h00 or ‘hff are allowed, but will trip the IDAC’s fault bit

(Fault_chn_a_idac = 1).

Verify that the IDAC is already connected, and that

Chn_a_idac_con is high.

Ensure that servo mode is not enabled for the channel

being programmed. Chn_a_servo_en must be low. This

requirement prevents the user from interfering with a

previously requested servo operation.

Update the CHn_A_IDAC() register with Chn_a_idac_pol,

Chn_a_idac_con = 1, Chn_a_idac_en = 1, and Chn_a_

idac[7:0].

Note: Care should be taken to preserve the current value

of the Chn_a_idac_pol bit, since the LTC2970 does not

prevent the user from changing this value when writing

to the IDAC control registers.

Rules:

Setting Chn_a_idac_con to zero will not disconnect the

DAC unless Chn_a_idac_en is also set low.

All Hard Connect rules apply.

8. Disconnecting the LTC2970 from the Power Supply

Trim Pin

VOUTn can be placed in a high impedance state simply by

clearing the Chn_a_idac_en bit. In order to minimize the

resulting disturbance to the power supply voltage, the

IDAC code should not be changed from its current value

when clearing the Chn_a_idac_en bit. This is not an issue

if the channel’s associated servo_en bit is high.

Disconnect Procedure:

Update CHn_IDAC() with Chn_a_idac_en set low.

The LTC2970 will immediately disconnect the buffered

IOUTn from VOUTn.

Disconnect Rules:

Clearing Chn_a_idac_con with Chn_a_idac_en high will

not disconnect the IDAC. Only setting Chn_a_idac_en low

will clear Chn_a_idac_con.

LTC2970-1 Only: Chn_a_idac_en may not be changed if

the feedback node connection is conﬁgured for tracking.

Tracking is enabled when GPIO_CFG is high and either

GPIO_0 or GPIO_1 are high.

9. Tracking Power Supplies Overview (LTC2970-1

Only)

The LTC2970-1 tracking feature allows the I2C interface

to initiate a controlled power up or power down of two

or more supplies (Figure 2 shows a typical LTC2970-1

application circuit). Multiple LTC2970-1’s with different

addresses may be simultaneously programmed using

the LTC2970 group address and the SYNC() command.

Tracking is enabled when GPIO_CFG is pulled high and

either GPIO_0 or GPIO_1 are high.

10. Tracking Power Supplies On (LTC2970-1 Only)

The LTC2970-1 tracking feature allows the I2C to initiate

a controlled power up of two or more supplies.

Procedure: This procedure describes all the steps neces-

sary to track up two or more power supplies. Steps that

require I2C interaction are preﬁxed with the required I2C

command function.

Power-up the LTC2970-1 with GPIO_CFG pulled high.

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