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参数资料
| 型号： | TC2576VAT |
| 元件分类： | 稳压器 |
| 英文描述： | 7.5 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PSFM5 |
| 封装： | TO-220, 5 PIN |
| 文件页数： | 7/25页 |
| 文件大小： | 213K |
| 代理商： | TC2576VAT |
15
TC2576
TC2576-2 12/04/00
3.0A Step-Down Switching Regulator
2001 Microchip Technology Inc.
DS21399A
Thermal Analysis and Design
The following procedure must be performed to deter-
mine whether or not a heatsink will be required. First
determine:
1. PD (max) – maximum regulator power dissipation in the
application.
2. TA(max) – maximum ambient temperature in the
pplication.
3. TJ(max) – maximum allowed junction temperature
(125
°C for the TC2576). For a conservative design, the
maximum junction temperature should not exceed 110
°C
to assure safe operation. For every additional +10
°C tem-
perature rise that the junction must withstand, the estimated
operating lifetime of the component is halved.
4.
ΘJC – package thermal resistance junction–case.
5.
ΘJA – package thermal resistance junction–
ambient.
(Refer to Absolute Maximum Ratings on page 2 of this
data sheet or
ΘJC and ΘJA values).
The following formula is to calculate the approximate
total power dissipated by the TC2576:
PD = (VIN x IQ ) + d x ILOAD x VSAT
where d is the duty cycle and for buck converter
d =
tON
=
VO
T
VIN
IQ (quiescent current) and VSAT can be found in the
TC2576 data sheet,
VIN is minimum input voltage applied,
VO is the regulator output voltage,
ILOAD is the load current.
The dynamic switching losses during turn–on and turn–
off can be neglected if a proper type catch diode is used.
Packages (Free–Standing)
For a free-standing application when no heatsink is
used, the junction temperature can be determined by the
following expression:
TJ = (ΘJA ) (PD ) + T A
where (
ΘJA )(PD ) represents the junction temperature
rise caused by the dissipated power and TA is the maxi-
mum ambient temperature.
Some Aspects That can Influence
Thermal Design
It should be noted that the package thermal resistance
and the junction temperature rise numbers are all approxi-
mate, and there are many factors that will affect these
numbers, such as PC board size, shape, thickness, physical
position, location, board temperature, as well as whether the
surrounding air is moving or still.
Other factors are trace width, total printed circuit copper
area, copper thickness, single– or double–sided, multilayer
board, the amount of solder on the board or even color of the
traces.
The size, quantity and spacing of other components on
the board can also influence its effectiveness to dissipate
the heat.
ADDITIONAL APPLICATIONS
Inverting Regulator
An inverting buck–boost regulator using the TC2576
(12V) is shown in Figure 8. This circuit converts a positive
input voltage to a negative output voltage with a common
ground by bootstrapping the regulators ground to the
negative output voltage. By grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it.
In this example the TC2576 (12V) is used to generate a
–12V output. The maximum input voltage in this case
cannot exceed 28V because the maximum voltage appear-
ing across the regulator is the absolute sum of the input and
output voltages and this must be limited to a maximum of
40V.
Figure 8. Inverting Buck-Boost Develops (12V)
D1
1N5822
L1
68
H
Output
GND
2
5
4
Feedback
12 to 40V
Unregulated
DC Input
1
3
R247k
ON/OFF
+VIN
–12V @ 700A
Regulated
Output
TC2576
(12V)
COUT
2200
F
CIN
100
F
/50V
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