Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

UCC28251 Datasheet(PDF) 17 Page - Texas Instruments

Part No. UCC28251
Description  UCC28251 Advanced PWM Controller With Prebias Operation
Download  55 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
Logo 

UCC28251 Datasheet(HTML) 17 Page - Texas Instruments

Zoom Inzoom in Zoom Outzoom out
 17 / 55 page
background image
50
150
250
350
450
550
650
750
850
950
1050
1150
1250
1350
0
50
100
150
200
RT (k
TDps=40ns
TDps=100ns
C00
-
´
=
D(SP)
SW
T
1
t
2 f
R
66.4pF
UCC28251
www.ti.com
SLUSBD8E – FEBRUARY 2013 – REVISED DECEMBER 2014
Feature Description (continued)
8.3.4 RT (Oscillator Frequency Set and Synchronization) (15/2)
The UCC28251 oscillator frequency is set by an external resistor connected between the RT pin and ground. The
oscillator frequency can be set to any value between 50 kHz to 1.4 MHz, which is equivalent to an 25-kHz to
700-kHz switching frequency. Switching frequency selection is a trade-off between efficiency and component
size. Based on the selected switching frequency, the programming resistor value can be calculated as:
(3)
In this equation, fSW is the switching frequency and TD(sp) is the dead time between synchronous rectifier turn-off
to primary switch turn-on. TD(sp) is set by an external resistor between the SP pin and ground (refer to the SP pin
description).
Each output (OUTA, OUTB, SRA, SRB) switches at half the oscillator frequency (fSW = ½ x fOSC). Figure 24
shows the relationship between RT and fOSC at certain TD(sp) and can be used to program oscillator frequency
accordingly.
Figure 24. Oscillator Frequency FOSC vs External Resistance of Rt at TD(ps) = 40 ns and 100 ns
The UCC28251 can be synchronized to an external clock by applying an external clock source to the RT pin.
Synchronization helps with parallel operation and/or preventing beat frequency noise. The UCC28251
synchronizes its internal oscillator to an external frequency source ranging from 84 kHz to 1.89 MHz, which is
equivalent to an 42-kHz to 0.945-MHz switching frequency. The internal oscillator frequency is clamped to 84
kHz during synchronization if the external source frequency drops below 84 kHz.
The UCC28251 aligns the turn-on of primary outputs OUTA and OUTB to the falling edge of the synchronizing
signal, as shown in Figure 25. If the frequency source is from the gate outputs of another half bridge controller,
interleaving can be achieved. The interleaving angle is determined by the frequency source’s duty cycle. When a
50% duty cycle is applied, optimal interleaving is achieved, and EMI filters can be minimized.
Copyright © 2013–2014, Texas Instruments Incorporated
Submit Documentation Feedback
17
Product Folder Links: UCC28251


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55 


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn