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UCC28251 Datasheet(PDF) 26 Page - Texas Instruments

Part No. UCC28251
Description  UCC28251 Advanced PWM Controller With Prebias Operation
Download  55 Pages
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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UCC28251 Datasheet(HTML) 26 Page - Texas Instruments

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R
1
2
V
0.7 V
R
R
0.7 V
-
=
´
(
)
(
)
R
F
2
R
0.7 V
V
V
R
8.5
A
V
0.7 V
´
-
<
m ´
-
HICC
HICC
2.4 V
0.3 V
T
C
2.7 A
-
=
´
m
OC(delay )
HICC
0.6 V
T
C
75 A
=
´
m
0.3V
0.6V
2.4V
HICC
t
t
4V
SS
OUTA
OUTB
Normal
OC
Normal
OC
Hiccup
Soft Start
T
OCdealy
T
HICC
UCC28251
SLUSBD8E – FEBRUARY 2013 – REVISED DECEMBER 2014
www.ti.com
Feature Description (continued)
Figure 35. Cycle-by-Cycle Current Limit Delay Timer and Hiccup Restart Timer
As shown in Figure 35, cycle-by-cycle current limiting shut-down delay time is:
(13)
And hiccup-restart-time THICC is equal to:
(14)
As soon as the outputs are shut-down, the SS pin is pulled to ground internally until the hiccup restart timer is
reset after time duration THICC.
8.3.15 OVP/OTP (19/6)
The OVP/OTP pin provides multiple fault protection functions. If the voltage on the OVP/OTP pin exceeds 0.7 V,
a fault shutdown occurs. All outputs stop switching and stay off (low) during the shutdown, and the SS pin is
pulled to ground internally. Once the fault condition is cleared (i.e. OVP/OTP voltage drops below 0.7 V), the
UCC28251 enters hiccup mode. A soft-start cycle begins after the hiccup cycle is finished. An internal 8.5-µA
switched current source is used to create hysteresis.
If the external resistor divider runs from line voltage VIN, a line over voltage protection is implemented.
If the external resistor divider runs from the output voltage, output over voltage fault protection is achieved.
Figure 36 shows the over-voltage protection external configuration at the OVP/OTP pin.
According to the protection threshold VR and recovery threshold VF, choose an arbitrary R2 value. To ensure a
realistic solution, R2 needs to meet the following:
(15)
The other two resistors, R1 and R3 can be calculated.
(16)
26
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Product Folder Links: UCC28251


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