參數(shù)資料
型號： TPS40211DRCTG4
廠商： TEXAS INSTRUMENTS INC
元件分類： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO10
封裝： GREEN, PLASTIC, SON-10
文件頁數(shù)： 5/47頁
文件大?。?/td> 1375K
代理商： TPS40211DRCTG4
T
8
10
2
7
4
6
9
2
SW
T
SW
T
1
R
5.8
10
f
C
8
10
f
1.4
10
f
1.5
10
1.7
10
C
4
10
C
-
=
+
+
-
+
-
+
1
RC
150 mV
S
Q
R
+
8
5
VDD
GND
R
RC
C
RC
CLK
External Frequency
Synchronization
(optional)
V
IN
TPS40210/11
UDG-08063
www.ti.com
SLUS772D – MARCH 2008 – REVISED APRIL 2010
Setting the Oscillator Frequency
The oscillator frequency is determined by a resistor and capacitor connected to the RC pin of the TPS40210. The
capacitor is charged to a level of approximately VVDD/20 by current flowing through the resistor and is then
discharged by a transistor internal to the TPS40210. The required resistor for a given oscillator frequency is
found from either Figure 1 or Equation 5.
(5)
Where:
RT is the timing resistance in k
f SW is the switching frequency in kHz
CT is the timing capacitance in pF
For most applications a capacitor in the range of 68 pF to 120 pF gives the best results. Resistor values should
be limited to between 100 k
and 1 M as well. If the resistor value falls below 100 k, decrease the capacitor
size and recalculate the resistor value for the desired frequency. As the capacitor size decreases below 47 pF,
the accuracy of Equation 5 degrades and empirical means may be needed to fine tune the timing component
values to achieve the desired switching frequency.
Synchronizing the Oscillator
The TPS40210 and TPS40211 can be synchronized to an external clock source. Figure 20 shows the functional
diagram of the oscillator. When synchronizing the oscillator to an external clock, the RC pin must be pulled below
150 mV for 20 ns or more. The external clock frequency must be higher than the free running frequency of the
converter as well. When synchronizing the controller, if the RC pin is held low for an excessive amount of time,
erratic operation may occur. The maximum amount of time that the RC pin should be held low is 50% of a
nominal output pulse, or 10% of the period of the synchronization frequency.
Under circumstances where the duty cycle is less than 50%, a Schottky diode connected from the RC pin to an
external clock may be used to synchronize the oscillator. The cathode of the diode is connected to the RC pin.
The trip point of the oscillator is set by an internal voltage divider to be 1/20 of the input voltage. The clock signal
must have an amplitude higher than this trip point. When the clock goes low, it allows the reset current to restart
the RC ramp, synchronizing the oscillator to the external clock. This provides a simple, single-component method
for clock synchronization.
Figure 20. Oscillator Functional Diagram
Copyright 2008–2010, Texas Instruments Incorporated
13
Product Folder Link(s): TPS40210 TPS40211
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