參數資料
型號: TPS40180RGER
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: 0.05 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQCC24
封裝: GREEN, PLASTIC, VQFN-24
文件頁數: 15/52頁
文件大小: 1291K
代理商: TPS40180RGER
www.ti.com
Selecting Current Sense Network components
CS
L
R
C
R
=
÷
è
(17)
R
CS
L
C
CS
R
L
UDG-07033
Inductor
+
_
V
C
(
)
(
)
f
CS(max)
IN
OUT
L
SW
G
V
2 V
L
R
+
>
÷
è
(18)
SLVS753B – FEBRUARY 2007 – REVISED NOVEMBER 2007
Some consideration must be given to selecting the components that are used to sense current in the converter. If
an R-C filter across the inductor is used, the R-C time constant should match the natural time constant of the
inductor. Equation 17 and Figure 27 describe the relationship.
Figure 27. Current Sense Network
The amplitude of the VC voltage must also be considered. If the VC voltage is expected to rise above 60 mV at
the desired overcurrent threshold, an attenuator should be used to keep the voltage to a maximum of 60 mV. To
implement the divider, place a resistor in parallel with CCS. The time constant of the whole network should remain
the same as the L/R time constant of the inductor.
High ripple current applications can also cause problems under certain conditions. When the sensing network is
matched to the inductor, the ripple voltage on the capacitor CCS is the same as the ripple voltage produced on
the effective inductor resistance. If this ripple component is too great, sub-harmonic instability can result and the
PWM exhibits excessive jitter or give a long pulse, short pulse type of output. To minimize this effect, the slope of
the signal presented to the current sense amplifier must be less than a maximum value. This places a minimum
limit on what the inductor L/R time constant can be for a given application as shown in Equation 18. If the chosen
inductor and other application parameters fall outside these recommendations, it is necessary to attenuate the
current feedback signal with an extra resistor.
where
L is the inductance in H
R
L is the equivalent series resistance of the inductor in
G
CS(max) is the maximum gain of the current sense amplifier, 13.75
V
IN is the input voltage in V
V
OUT is the output voltage in V
f
SW is the switching frequency in Hz
22
Copyright 2007, Texas Instruments Incorporated
Product Folder Link(s): TPS40180
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