IMP3 7
Application Information
The IMP37 voltage regulator ICs offer self-protection features
which include short-circuit current protection and automatic thermal
shutdown (for junction temperature above 165°C).
Thermal Management
The maximum operating junction temperature for the IMP37 devices
is 150°C. The junction temperature can be calculated when the
power dissipation and ambient temperature are known with this
equation: T
J
= T
A
+ (P
D
x
Θ
JA
).
The thermal resistance from juntion-to-ambient (Θ
JA
) is the sum of
the three thermal resistances:
Θ
JA
=
Θ
JT
+
Θ
TS
+
Θ
SA
Where
Θ
JT
= Junction-to-Tab thermal resistance
Θ
TS
= Tab-to-Heat Sink thermal resistance
Θ
SA
= Heat Sink-to-Air thermal resistance
Circuit Stability
Like all regulators, an output filter capacitor is required for circuit sta-
bility. Besides smoothing the output, the output capacitor
“completes” the regulator’s frequency compensation. The ESR of the
output capacitor should be less than 0.5Ω. Low ESR capacitors are
preferred.
Table 1
shows recommended minimum capacitance values for both
aluminum and tantalum capacitors. Larger values of output capaci-
tance do not cause stability problems.
Table 1. Recommended Output Bypass Capacitors
Output Bypass Capacitor (ESR < 0.5
Ω)
10
µ
F Tantalum, 100
µ
F Aluminum
An input bypass capacitor is recommended. A 10µF or larger tanta-
lum capacitor is suitable for most applications.
Table 2. Thermal Resistance of Packages
Package Type
SOT-223
TO-263
Thermal Resistance
Junction to Tab,
Θ
JT
15°C/W
10°C/W
The IMP37 series devices have thermal limiting circuitry to protect
the device from over current. For continuous operation, the maxi-
mum junction temperature rating must not be exceeded.
IMP37
V
IN
*
IN
OUT
GND
3.3V
+
+
**
* Min. 15µF Tantalum or 100µF Aluminum.
Capacitor May Be Increased Without Limit.
** 10µF Tantalum or 100µF Aluminum
37_02.eps
Figure 1. Fixed 3.3V Regulator
4
408-432-9100/www.impweb.com
©
1999 IMP, Inc.
IMP [ IMP, INC ]
