參數(shù)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(shù): 30/52頁
文件大?。?/td> 1291K
代理商: TPS40180RGER
www.ti.com
RIPPLE
RIPPLE(TotOUT)
RIPPLE(COUT)
OUT
SW
Co
RIPPLE
I
V
8 C
f
ESR
I
-
÷
-
è
=
(22)
Step 3: Input Capacitor Selection
f
OUT
IN(min)
RIPPLE(Cin)
IN
SW
I
V
C
V
=
(23)
RIPPLE(CinESR)
Cin
1
OUT
RIPPLE
2
V
ESR
I
=
+
(24)
RMS _ CIN
OUT
I
D
(1 D)
I
=
-
(25)
MOSFET Selection
2
RIPPLE
rms
OUT
I
Isw
D
I
7.08 A
12
÷
=
+
=
÷
è
(26)
(
)
2
SW(cond)
SWrms
DS(on)(sw )
P
I
R
0.47 W
=
=
(27)
(
)
PK
IN
SW
DRV
SW
SW(sw )
I
V
f
R
Qgd
Qgs
P
0.35 W
Vgtdrv
+
=
(28)
SLVS753B – FEBRUARY 2007 – REVISED NOVEMBER 2007
With an 880-
F output capacitance, the ripple voltage at the capacitor is calculated to be 1.5 mV. In the
specification, the output ripple voltage should be less than 30 mV, so based on Equation 22, the required
maximum ESR is 9.4 m
. The selected capacitors can meet this requirement.
The input voltage ripple depends on input capacitance and ESR. The minimum capacitor and the maximum ESR
can be estimated by:
For this design, assume VRIPPLE(Cin) is 100 mV and VRIPPLE(CinESR) is 50 mV, so the calculated minimum
capacitance is 89
F and the maximum ESR is 2.3 m. Choosing four 22 F, 16 V, 2m ESR ceramic
capacitors meets this requirement.
Another important thing for the input capacitor is the RMS ripple current rating. The RMS current in the input
capacitor is estimated by:
where
D is the duty cycle
The calculated RMS current is 6.6 A. Each selected ceramic capacitor has a RMS current rating of 4.3 A, so it is
sufficient to reach this requirement.
The MOSFET selection determines the converter efficiency. In this design, the duty cycle is very small so that
the high-side MOSFET is dominated with switching losses and the low-side MOSFET is dominated with
conduction loss. To optimize the efficiency, choose smaller gate charge for the high-side MOSFET and smaller
RDS(on) for the low-side MOSFET. RENESAS HAT2167H and HAT2164H are selected as the high-side and
low-side MOSFET respectively. The power losses in the high-side MOSFET is calculated with the following
equations:
The RMS current in the high-side MOSFET is
The RDS(on)(sw) is 9.3 m when the MOSFET gate voltage is 4.5 V. The conduction loss is:
The switching loss is:
The calculated total loss is the high-side MOSFET is:
36
Copyright 2007, Texas Instruments Incorporated
Product Folder Link(s): TPS40180
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