IMP37
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: TJ = TA + (PD x ΘJA).
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.
The thermal resistance from juntion-to-ambient (ΘJA) is the sum of
the three thermal resistances:
ΘJA = ΘJT + ΘTS + ΘSA
Where ΘJT = Junction-to-Tab thermal resistance
ΘTS = Tab-to-Heat Sink thermal resistance
ΘSA = Heat Sink-to-Air thermal resistance
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
Table 2. Thermal Resistance of Packages
Output Bypass Capacitor (ESR < 0.5Ω)
10µF Tantalum, 100µF Aluminum
Thermal Resistance
Package Type
Junction to Tab, Θ
An input bypass capacitor is recommended. A 10µF or larger tanta-
JT
lum capacitor is suitable for most applications.
SOT-223
TO-263
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
VIN
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
408-432-9100/www.impweb.com
© 1999 IMP, Inc.
4
IMP [ IMP, INC ]
