參數(shù)資料
型號(hào): TPS53314RGFR
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: SWITCHING REGULATOR, 1070 kHz SWITCHING FREQ-MAX, PQCC40
封裝: 5 X 7 MM, GREEN, PLASTIC, VQFN-40
文件頁(yè)數(shù): 13/29頁(yè)
文件大小: 800K
代理商: TPS53314RGFR
R1
R2
Voltage
Divider
37
+
VFB
+
0.6 V
PWM
Control
Logic
and
Divider
VIN
L
ESR
COUT
VC
RLOAD
IIND
IOUT
UDG-10203
IC
Switching Modulator
Output
Capacitor
VOUT
TPS53314
LL
VIN
( ) =
OUT
1
H s
s
ESR
C
=
p
SW
0
OUT
f
1
f
2
ESR
C
4
SLUSAK3
– MAY 2011
Small Signal Model
From small-signal loop analysis, a buck converter using D-CAP
mode can be simplified as shown in Figure 37.
Figure 37. Simplified Modulator Model
The output voltage is compared with the internal reference voltage (ramp signal is ignored here for simplicity).
The PWM comparator determines the timing to turn on the high-side MOSFET. The gain and speed of the
comparator can be assumed high enough to keep the voltage at the beginning of each on-cycle substantially
constant.
(1)
For the loop stability, the 0 dB frequency,
0, defined in Equation 2 must be lower than of the switching
frequency.
(2)
According to Equation 2, the loop stability of D-CAP
mode modulator is mainly determined by the capacitor
chemistry. For example, specialty polymer capacitors (SP-CAP) have COUT on the order of several 100 F and
ESR in range of 10 m
Ω. These makes 0 on the order of 100 kHz or less and the loop is stable. However,
ceramic capacitors have an
0 at more than 700 kHz, and need special care when used with this modulator. An
application circuit using ceramic capacitors is described in External Parts Selection section under All Ceramic
Output Capacitors.
Ramp Signal
The TPS53314 adds a ramp signal to the 0.6-V reference in order to improve jitter performance. The feedback
voltage is compared with the reference information to keep the output voltage in regulation. By adding a small
ramp signal to the reference, the signal-to-noise ratio at the onset of a new switching cycle is improved.
Therefore the operation becomes less jittery and more stable. The ramp signal is controlled to start with
–7 mV at
the beginning of an on-cycle and becomes 0 mV at the end of an off-cycle in steady state.
20
Copyright
2011, Texas Instruments Incorporated
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