MICROELECTRONICS
A
A
Power Management
GM1117
1.0A LOW DROPOUT PRECISION LINEAR REGULATORS
Protection Diodes
When large external capacitors are used with most
linear regulator, it is wise to add protection diodes. If
the input voltage of the regulator is shorted, the out-
put capacitor will discharge into the output of the reg-
ulator. The discharge current depends on the value
of capacitor, output voltage, and rate at which V
IN
drops.
Figure 2
Protection Diode Scheme for
Large Output Capacitors
(a),(b)
Output Voltage Sensing
The GM1117 are three terminal regulators. For which,
they cannot provide true remote load sensing. Load
regulation is limited by the resistance of the conductors
connecting the regulator to the load. For best results
the GM1117 should be connected are as shown in
Figure 3.
V
IN
V
IN
V
OUT
R
C
Conductor
Parasitic
Resistance
R
LOAD
GM1117-3.3
GND
(a) Fixed Version
(a) Fixed Version
IN4002
V
IN
V
IN
V
OUT
V
OUT
V
IN
C2
V
IN
ADJ
V
OUT
R
C
R1
R2
(b) Adjustable Version
(b) Adjustable Version
Figure 3
(a),(b)
Conductor Parasitic Resistance Effects are
Minimized by this Grounding Scheme For Fixed
and Adjustable Output Regulators
GM1117-3.3
C1
GND
Conductor
Parasitic
Resistance
R
LOAD
GM1117-Adj
IN4002
V
IN
V
IN
V
OUT
V
OUT
GM1117-Adj
C1
ADJ
R1
C
ADJ
C2
Calculating Power Dissipation and Heat
Sink Requirements
R2
The GM1117 precision linear regulators include thermal
shutdown and current limit circuitry to protect the de-
In the GM1117 linear regulators, the discharge path
is through a large junction, and protection diodes are
normally not needed. However, damage can occur if
the regulator is used with large output capacitance
values and the input voltage is instantaneously
shorted to ground. In this case, a diode connected
as shown above in Figure 2.
vices. However, high power regulators normally oper-
ate at high junction temperatures. It is important to cal-
culate the power dissipation and junction temperatures
accurately to be sure that you use and adequate heat
sink. The case is connected to V
OUT
on the GM1117,
and electrical isolation may be required for some appli-
cations. Thermal compound should always be used
with high current regulators like the GM1117.
GM1117
7
GAMMA [ GAMMA MICROELECTRONICS INC. ]
