Datasheet

VREF
OVP
UCC28250
+
0.7 V
11 mA
R3
R1
PTC
4 NTC1
0.7 V
R R
3.3 V 0.7 V
= ´
-
VREF
OVP
UCC28250
+
0.7 V
11 mA
R3
R1
R2
VIN or VOUT
NTC
R4
UCC28250
www.ti.com SLUSA29C –APRIL 2010– REVISED JULY 2011
Figure 18. Over Temperature Protection
Figure 19 shows an external configuration using the OVP/OTP pin to achieve both over-voltage and over
temperature protection. Follow the same design procedure for the OVP setting to choose R
1
, R
2
, and R
3
. Choose
an NTC value at protection temperature much smaller than R
1
and with the resistance at protection temperature
as R
NTC1
, and recover temperature as R
NTC2
. The R4 value can be calculated as:
(22)
Because of the interaction between the two voltage dividers, over temperature protection thresholds move
slightly with the different input voltages.
Figure 19. Over Voltage and Over Temperature Protection With Single OVP Pin
OUTA (9/16) and OUTB (8/15)
OUTA and OUTB are the primary-side switch control signals. With the 0.2-A peak current capability, an external
gate driver is required.
SRA (7/14) and SRB (6/13)
SRA and SRB are the synchronous rectifier control signals. With the 0.2A peak current capability, an external
gate driver is required.
GND (4/11)
GND pin is the ground reference for the whole device. Tie all the signal returns to this pin.
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