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UCC28251 Datasheet(PDF) 4 Page - Texas Instruments

Part No. UCC28251
Description  UCC28251 Advanced PWM Controller With Prebias Operation
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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UCC28251 Datasheet(HTML) 4 Page - Texas Instruments

 
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16
17
18
19
20
10
9
8
7
6
15
14
13
12
11
1
2
3
4
5
RAMP/CS
ILIM
EN
OVP/OTP
VREF
SRB
SRA
OUTB
OUTA
HICC
RT
VSENSE
SS
SP
PS
REF/EA+ FB/EA- COMP
GND
VDD
QFN-20
TOP VIEW
15
14
13
12
11
10
9
8
7
6
16
17
18
19
20
1
2
3
4
5
RAMP/CS
ILIM
EN
OVP/OTP
VREF
SRB
SRA
OUTB
OUTA
HICC
RT
VSENSE
SS
SP
PS
REF/EA+
FB/EA-
COMP
GND
VDD
TSSOP-20
TOP VIEW
UCC28251
SLUSBD8E – FEBRUARY 2013 – REVISED DECEMBER 2014
www.ti.com
5 Description (continued)
Externally programmable soft-start, used in conjunction with an internal pre-biased startup circuit, allows the
controller to gradually reach a steady-state operating point under all output conditions. The UCC28251 can be
configured for primary or secondary-side control and either voltage or current mode control can be implemented.
The oscillator operates at frequencies up to 1.8 MHz, and can be synchronized to an external clock. Input
voltage feedforward, cycle-by-cycle current limit, and a programmable hiccup timer allow the system to stay
within a safe operation range. Input voltage, output voltage and temperature protection can be implemented.
Dead time between primary-side switch and secondary-side synchronous rectifiers can be independently
programmed.
6 Pin Configuration and Functions
Pin Functions
PIN
I/O
DESCRIPTION
QFN-20
PW-20
NAME
5
12
VDD
I
Bias supply input.
20
7
VREF
O
3.3-V reference output.
18
5
EN
I
Device enable and disable.
15
2
RT
I
Oscillator frequency set or synchronous clock input.
12
19
SP
I
Synchronous rectifier off to primary on dead-time set .
11
18
PS
I
Primary off to synchronous rectifier on dead-time set .
PWM ramp input (for voltage mode control) or current sense input (for current
16
3
RAMP/CS
I
mode control).
1
8
REF/EA+
I
Error amplifier non-inverting input.
2
9
FB/EA-
I
Error amplifier inverting input.
3
10
COMP
I/O
Error amplifier output.
14
1
VSENSE
I
Output voltage sensing for pre-bias control.
13
20
SS
I/O
Soft-start programming.
17
4
ILIM
I
Current sense for cycle-by-cycle over-current protection.
10
17
HICC
I
Cycle-by-cycle current limit time delay and Hiccup time setting.
19
6
OVP/OTP
I
Over voltage and over temperature protection pin.
9
16
OUTA
O
0.2-A sink/source primary switching output.
8
15
OUTB
O
0.2-A sink/source primary switching output.
4
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Copyright © 2013–2014, Texas Instruments Incorporated
Product Folder Links: UCC28251


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