Datasheet

7
TPS40170
FB
UDG-09208
R1
R2
+
+
+
V
REF
FB
COMP
V
OUT
6
TRK
SS
EAMP
TRK IN
TRK
( )
+
= ´
OUT REF
R1 R2
V V
R2
( )
+
= ´
OUT TRK
R1 R2
V V
R2
TPS40170
www.ti.com SLUS970A –MARCH 2011–REVISED NOVEMBER 2013
Tracking
The TRK pin is used for output voltage tracking. The output voltage is regulated so that the FB pin equals the
lowest of the internal reference voltage (V
REF
) or the level-shifted SS pin voltage (SS
EAMP
) or the TRK pin
voltage. Once the TRK pin goes above the reference voltage, then the output voltage is no longer governed by
the TRK pin, but it is governed by the reference voltage.
If the voltage tracking function is used, then it should be noted that the SS pin capacitor must remain connected
as the SS pin and is also used for FAULT timing. For proper tracking using the TRK pin, the tracking voltage
should be allowed to rise only after SS
EAMP
has exceeded V
REF
, so that there is no possibility of the TRK pin
voltage being higher than the SS
EAMP
voltage. From Figure 21, for SS
EAMP
= 0.6 V, the SS pin voltage is typically
1.7 V.
The maximum slew rate on the TRK pin should be determined by the output capacitance and feedback loop
bandwidth. A higher slew rate can possibly trip overcurrent protection.
Figure 26 shows the tracking functional block. For SS
EAMP
voltages greater than TRK pin voltage, the V
OUT
is
given by Equation 12 and Equation 13.
.
For 0 V < V
TRK
< V
REF
.
(12)
.
For V
TRK
> V
REF
.
(13)
Figure 26. Tracking Functional Block
There are three potential applications for the tracking function.
• simultaneous voltage tracking
• ratiometric voltage tracking
• sequential startup mode
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