Datasheet

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RIPPLE
OC CS
LIM
ILIM
I
I DCR A
2
R
I
R1
C1
L
DCR
10 mA
ILIM1
L1
V
OUT1
SW1
UDG-11114
+
R
ILIM
+
OC
A
CS
=15
CS1–CS1+
I
OUT
TPS40322
SLUSAF8D –JUNE 2011–REVISED JANUARY 2014 www.ti.com
Overcurrent Protection
The TPS40322 has dedicated ILIM pins for each channel for use when operating in dual-output mode. When
operating in two-phase mode, both channels share the same overcurrent level set by ILIM1. The overcurrent
level is set with a resistor connected from the ILIMx pin to analog ground. The sensed current signal is amplified
by the CS amplifier with a gain of 15, and then compared with the established overcurrent level to determine if
there is an OC fault. This design is shown in Figure 17.
Figure 17. Overcurrent Protection
Equation 3 shows the current limit resistance (R
LIM
) calculation for desired overcurrent limit.
where
• I
OC
is the desired DC over current limit level
• I
RIPPLE
is the inductor peak-peak ripple current
• DCR is the inductor DC resistance
• A
CS
is the current sensing amplifier gain (typically 15)
• I
ILIM
is the internal source current out of ILIMx pin (typically 10 µA) (3)
The TPS40322 implements cycle-by-cycle current limit when the inductor peak current has exceeded the set
limit. When the controller counts three consecutive clock cycles of an overcurrent condition, the high-side and
low-side MOSFETs are turned off and the controller enters a hiccup mode. After six soft-start cycles, normal
switching is attempted. If the overcurrent has cleared, normal operation resumes, otherwise the sequence
repeats.
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