参数资料
型号: TPS40052PWP
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封装: GREEN, PLASTIC, HTSSOP-16
文件页数: 16/33页
文件大小: 753K
代理商: TPS40052PWP
TPS40052
SLUS563C AUGUST 2003 REVISED FEBRUARY 2005
23
www.ti.com
DESIGN EXAMPLE
4. Calculate the power losses
Power losses in the high-side MOSFET (Si7860DP) at 14.4-VIN where switching losses dominate can be
calculated from equation (29).
I
RMS + IO
d
+ 8
0.086
+ 2.35 A
substituting (28) into (27) yields
P
COND + 2.35
2
0.008
(1
) 0.007
(150
* 25)) + 0.083 W
and from equation (29), the switching losses can be determined.
P
SW(fsw) + VIN
I
O
t
SW
f
SW + 14.4 V
8A
20 ns
170 kHz
+ 0.39 W
The MOSFET junction temperature can be found by substituting equation (31) into equation (30)
T
J + PCOND ) PSW
q
JA ) TA +
(0.083
) 0.39)
40
) 85 + 90OC
5. Calculate synchronous rectifier losses
The synchronous rectifier MOSFET has two loss components, conduction, and diode reverse recovery losses.
The conduction losses are due to IRMS losses as well as body diode conduction losses during the dead time
associated with the anti-cross conduction delay.
The IRMS current through the synchronous rectifier from (32)
I
RMS + IO
1
* d + 8
1
* 0.126 + 7.48 A
RMS
The synchronous MOSFET conduction loss from (27) is:
P
COND + 7.48
2
0.008
(1
) 0.007(150 * 25)) + 0.83 W
The body diode conduction loss from (33) is:
P
DC + 2
I
O
V
FD
t
DELAY
f
SW + 2
8.0 A
0.8 V
100 ns
170 kHz
+ 0.218 W
The body diode reverse recovery loss from (34) is:
P
RR + 0.5
Q
RR
V
IN
f
SW + 0.5
30 nC
14.4 V
170 kHz
+ 0.037 W
The total power dissipated in the synchronous rectifier MOSFET from (35) is:
P
SR + PRR ) PCOND ) PDC + 0.037 ) 0.83 ) 0.218 + 1.085 W
The junction temperature of the synchronous rectifier at 85
°C is:
T
J + PSR
q
JA ) TA +
(1.085)
40
) 85 + 128oC
In typical applications, paralleling the synchronous rectifier MOSFET with a Schottky rectifier increases the
overall converter efficiency by approximately 2% due to the lower power dissipation during the body diode
conduction and reverse recovery periods.
(45)
(46)
(47)
(48)
(49)
(50)
(51)
(52)
(53)
(54)
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