Datasheet
2
o
c
S
V (1 D)
I =
f 2 L
-g
g g
(1)
in
L
S
V D
i =
L f
D
g
g
+
out
in
sw
I
V D
I =
2 f L 1 D-
g
g g
(2)
Overvoltage Protection
Short-Circuit Protection
Soft-Start Operation
Start-Up Sequencing
8.7ms
V
pos
V
neg
T0298-01
Output-Current Mismatch
Input Capacitor Selection
TPS65136
www.ti.com
............................................................................................................................................................. SLVS831A – APRIL 2008 – REVISED JULY 2008
The inductor ripple current when operating in CCM can also be calculated.
Last but not least, the converter switch peak current is calculated.
The device monitors both the positive and negative output voltages. The positive regulator monitors the positive
output and reduces the current limit when the output voltage exceeds the overvoltage protection limit. The
negative output is clamped using a zener diode, typically to – 7.6 V.
Both outputs are protected against short circuits either to GND or against the other output. For the positive
output, the device switching frequency and the current limit are reduced in case of a short circuit.
The device increases the current limit during soft-start operation to avoid high inrush currents during start-up.
The current limit typically ramps up to its full-current limit within 100 µ s.
The TPS65136 includes an internal, fixed start-up sequence, where the negative output voltage rail comes up
after the positive output voltage rail. The device starts the positive rail first, and an internal counter delays the
start-up of the negative rail, typically by 8.7 ms. The negative rail is clamped, typically to – 0.4 V, until the internal
timer commands the negative rail to start up.
Figure 15. Start-Up Sequencing
The device operates best when the current of the positive output is similar to the current of the negative output.
However, the device is able to regulate an output-current mismatch between the outputs of up to 30%. If the
output-current mismatch becomes much larger, then one of the outputs goes out of regulation.
The device typically requires a 10- µ F ceramic input capacitor. Larger values can be used to lower the input
voltage ripple. Table 1 lists capacitors suitable for use on the TPS65136 input.
Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Link(s): TPS65136