TPS65135 Datasheet, PDF (12/21 Pages) Texas Instruments – Single-Inductor, Multiple-Output (SIMO) Regulator

TPS65135
SLVS704A – NOVEMBER 2011 – REVISED NOVEMBER 2011
V_in I_p
L
V_pos V_neg
L
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A
A
t_clock
M0116-01
Figure 17. Inherently Perfect Line-Transient Regulation
The converter always sees the sum of the negative and positive output voltage, which is calculated as:
V
O
=
V
OUTP
+
V
OUTN
(1)
The converter duty cycle is calculated using the efficiency estimation from the data sheet curves or from real
application measurements. A 70% efficiency value is a good value to go through the calculations.
V
D=
O
h
×
V
IN
+
V
O
(2)
The output current for entering continuous conduction mode can be calculated. The switching frequency can be
obtained from the data sheet graphs. A frequency of 1.5 MHz is usually sufficient for these types of calculations.
I
C
=
V
O
×
(1-
D)²
f
S
×
2
×
L
(3)
The inductor ripple current when operating in CCM can also be calculated.
DI_L
=
V
IN
×D
L
×
f
S
(4)
Last but not least, the converter switch peak current is calculated as follows.
I_{L _ peak}
=
I_{OUT +}
1- D
1
2 ^{× DIL}
(5)
Overvoltage Protection
The device monitors the positive and negative output voltage. The regulators monitor the outputs and reduce the
current limit when the output voltages exceed the overvoltage protection limit. They are clamped using a zener
diode, the positive output to typically 7V and the negative to –7.6 V.
Short-Circuit Protection
Both outputs are protected against short circuits either to GND or against the other output. The device switching
frequency and the current limit are reduced in case of a short circuit.
Soft-Start Operation
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 µs.
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