參數(shù)資料
型號: TPS40050PWPRG4
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: 0.2 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封裝: GREEN, PLASTIC, HTSSOP-16
文件頁數(shù): 7/36頁
文件大?。?/td> 648K
代理商: TPS40050PWPRG4
TPS40050
TPS40051
TPS40053
SLUS540F DECEMBER 2002 REVISED JUNE 2004
www.ti.com
15
APPLICATION INFORMATION
SYNCHRONIZING TO AN EXTERNAL SUPPLY
The TPS4005x can be synchronized to an external clock through the SYNC pin. Synchronization occurs on the
falling edge of the SYNC signal. The synchronization frequency should be in the range of 20% to 30% higher
than its programmed free-run frequency. The clock frequency at the SYNC pin replaces the master clock
generated by the oscillator circuit. Pulling the SYNC pin low programs the TPS4005x to freely run at the
frequency programmed by RT.
The higher synchronization must be factored in when programming the PWM ramp generator circuit. If the PWM
ramp is interrupted by the SYNC pulse, a UVLO condition is declared and the PWM becomes disabled. Typically
this is of concern under low-line conditions only. In any case, RKFF needs to be adjusted for the higher switching
frequency.
In order to specify the correct value for RKFF at the synchronizing frequency, calculate a ’dummy’ value for RT
that would cause the oscillator to run at the synchronizing frequency. Do not use this value of RT in the design.
R
T(dummy) +
1
f
SYNC
17.82
10*6
* 23 kW
Use the value of RT(dummy) to calculate the value for RKFF.
R
KFF + VIN(min) * 3.5 V
58.14
R
T(dummy) ) 1340
W
This value of RKFF ensures that UVLO is not engaged when operating at the synchronization frequency.
D RT(dummy) is in k
LOOP COMPENSATION
Voltage-mode buck-type converters are typically compensated using Type III networks. Since the TPS4005x
uses voltage feedforward control, the gain of the PWM modulator with voltage feedforward circuit must be
included. The modulator gain is described in Figure 9, with VIN being the minimum input voltage required to
cause the ramp excursion to cover the entire switching period as described in equation (19).
A
MOD +
V
IN
V
S
or
A
MOD(dB) + 20
log
V
IN
V
S
Duty dycle, D, varies from 0 to 1 as the control voltage, VC, varies from the minimum ramp voltage to the
maximum ramp voltage, VS. Also, for a synchronous buck converter, D = VO / VIN. To get the control voltage
to output voltage modulator gain in terms of the input voltage and ramp voltage,
D
+
V
O
V
IN
+
V
C
V
S
or
V
O
V
C
+
V
IN
V
S
(17)
(18)
(19)
(20)
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