Datasheet

R5 + R6
ǒ
V
out
V
FB
* 1
Ǔ
+ R6 ǒ
V
out
1.213
* 1Ǔ
V
out
+ 1.213
ǒ
1 )
R5
R6
Ǔ
Q3
I
DRVP
DRP
Current
Control
SoftStart
V
V
GH
23V/50mA
C13
0.47 µF
FBP
C
fly
V
S
R5
R6
SUP =V
IN S
orV
TPS65161
TPS65161A, TPS65161B
www.ti.com SLVS617E –APRIL 2006–REVISED MARCH 2013
Soft Start (Step-Down Converter)
To avoid high inrush current during start-up, an internal soft start is implemented in the TPS65161. When the
step-down converter is enabled over EN1, its reference voltage slowly rises from zero to its power-good
threshold of typically 90% of V
ref
. When the reference voltage reaches this power-good threshold, the error
amplifier is released to its normal operation at its normal duty cycle. To further limit the inrush current during soft
start, the converter frequency is set to 1/4
th
of the switching frequency f
s
and then ½ of f
s
determined by the
comparator that monitors the feedback voltage. See the internal block diagram. Soft start is typically completed
within 1 ms.
Short-Circuit Protection (Step-Down Converter)
To limit the short-circuit current, the device has a cycle-by-cycle current limit. To avoid the short-circuit current
rising above the internal current limit when the output is shorted to GND, the switching frequency is reduced as
well. This is implemented by two comparators monitoring the feedback voltage. The step-down converter
switching frequency is reduced to ½ of f
s
when the feedback is below 0.9 V and to 1/4
th
of the switching
frequency when the feedback voltage is below 0.6 V.
Positive Charge Pump
The positive charge pump provides a regulated output voltage set by the external resistor divider. Figure 16
shows an extract of the positive charge-pump driver circuit. The operation of the charge-pump driver can be
understood best with Figure 16. During the first cycle, Q3 is turned on and the flying capacitor C
fly
charges to the
source voltage, V
S
. During the next clock cycle, Q3 is turned off and the current source charges the drive pin,
DRP, up to the supply voltage, V
(SUP)
. Because the flying capacitor voltage sits on top of the drive pin voltage,
the maximum output voltage is V
(SUP)
+V
S
. The SUP pin can be connected either to the input voltage V
IN
of the
TPS65161 or the output voltage of the main boost converter V
S
.
Figure 16. Extract of the Positive Charge-Pump Driver
If higher output voltages are required, another charge-pump stage can be added to the output.
Setting the output voltage:
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