LTC2970-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2970-1' PDF : 36 Pages View PDF
LTC2970/LTC2970-1
U
OPERATIO
5. Soft Connecting the LTC2970 to the Power Supply
Feedback Node
The soft connect feature allows the LTC2970 to connect to
the power supply’s feedback node with minimal disturbance
to the supply’s output voltage. This is accomplished by
comparing the buffered voltage of IOUTn to the voltage at
VOUTn and incrementing or decrementing Chn_a_idac[7:0]
until the comparator output (COMPn) changes. The value
of Chn_a_idac[7:0] when the comparator transitions is the
appropriate value for a soft connect. The voltage buffer
output is only connected to VOUTn if the IDAC reaches this
soft connect value without generating an instantaneous
IDAC fault (Fault_chn_a_idac).
Soft-Connect Procedure:
Determine the appropriate polarity for Chn_a_idac_pol.
Select Chn_a_idac_pol = 1 if incrementing VOUTn causes
differential voltage (VINn_AP – VINn_AM) to increase.
When properly programmed, lowering the value in Chn_
a_idac[7:0] will always cause the output of the controlled
power supply to decrease.
Ensure that the channel’s IDAC is not currently enabled for
connection, i.e., the Chn_a_idac_en bit must be 0.
Update CHn_A_IDAC() with Chn_a_idac_pol, Chn_a_idac_
con = 0, Chn_a_idac_en = 1, and Chn_a_idac[7:0] = 0x80.
The value programmed into Chn_a_idac[7:0] is ignored
and Chn_a_idac[7:0] is initially set to 8’h80.
The LTC2970 will now ramp Chn_a_idac[7:0] while moni-
toring the output of the soft connect comparator. If the soft
connect comparator trips, the LTC2970 will connect the
output of VBUFn to VOUTn and set Chn_a_idac_con high.
If the soft connect comparator does not trip before the
IDAC value reaches ‘h00 or ‘hFF, then the soft connection
will fail, an IDAC fault will be indicated (Fault_chn_a_idac),
and Chn_a_idac_con will remain low.
Soft-Connect Rules:
When both channels are requesting a soft connect, chan-
nel 0 has priority.
Soft connect requests will be ignored and the user will not
be able to change Chn_a_idac_pol or Chn_a_idac[7:0] if
the LTC2970 is servicing a previously issued soft connect
on that channel or the previously issued soft connect failed
with an IDAC fault (Fault_chn_a_idac = 1). Recall that the
Chn_a_idac_en bit must initially have been set to 0.
LTC2970-1 Only: Soft connect requests will be ignored
and the user will not be able to change Chn_a_idac_pol or
Chn_a_idac[7:0] if GPIO_CFG is high and either GPIO_0
or GPIO_1 are high.
LTC2970-1 Only: Soft connect requests will be ignored and
the user will not be able to change the Chn_a_idac_pol bit
if there is a pending tracking operation.
6. Hard Connecting the LTC2970 to the Power Supply
Trim Pin
The hard connect feature allows the LTC2970 to bypass the
soft connect algorithm and connect directly to the power
supply’s feedback node using the value programmed into
Chn_a_idac[7:0]. This feature is useful for systems that
have calculated or measured an acceptable voltage at which
to connect the IDAC’s buffered voltage VBUFn to VOUTn.
Hard Connect Procedure:
Determine the appropriate polarity for Chn_a_idac_pol.
Select Chn_a_idac_pol = 1 if incrementing VOUTn causes
(VINn_AP – VINn_AP) to increase. When properly pro-
grammed, lowering the value in the IDAC will always cause
the output of the controlled power supply to decrease.
Determine the value for Chn_a_idac[7:0]. The values ‘h00
or ‘hff are allowed, but they will trip the IDAC’s fault bit
(Fault_chn_a_idac = 1).
When the IDAC is already connected, the value Chn_a_
idac[7:0] and Chn_a_idac_pol will be programmed into the
IDAC provided all other conditions are met. See “Program-
ming a Previously Connected Current DAC” for details
Update CHn_A_IDAC() with Chn_a_idac_pol, Chn_a_idac_
con = 1, Chn_a_idac_en = 1, and Chn_a_idac[7:0].
Hard Connect Rules:
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 the LTC2970 is servicing a previously
issued soft connect on that channel or the previously issued
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