Power Management
MICROELECTRONICS
A
A
GM66500 SERIES
5A ULTRA LOW - DROPOUT REGULATOR
Calculate the power dissipation of the regulator from
these numbers and the device parameters from this
datasheet, where the ground current is taken from
data sheet
P
D
= (V
IN
- V
OUT
)I
OUT
+ V
IN
I
GND
APPLICATION INFORMATION
The GM66500 series is a high-performance low-
dropout voltage regulator, suitable for moderate to
high-current voltage regulator applications. Its 400mV
dropout voltage at full load makes it especially valuable
in battery-powered systems and as a high-efficiency
noise filter in post-regulator applications.
Unlike older NPN-pass transistor designs, where the
minimum dropout voltage is limited by the base-to-
emitter voltage drop and collector-to-emitter saturation
voltage, dropout performance of the PNP output of
these devices is limited only by the low V
CE
saturation
Voltage.
The GM66500 series regulator is fully protected from
damage due to fault conditions. Current limiting is
provided. This limiting is linear, output current during
overload conditions is constant. Thermal shutdown
disables the device when the die temperature exceeds
the maximum safe operating temperature. Transient
protection allows device (and load) survival even when
the input voltage spikes above and below nominal. The
output structure of these regulators allows voltages in
excess of the desired output voltage to be applied
without reverse current flow.
The heat sink thermal resistance is determined by:
T
J(MAX)
- TA
q
SA
=
- (q
JC
+ q
CS
)
P
D
where T
J(max)
2°C/W.
The heat sink may be significantly reduced in
applications where the minimum input voltage is
known and is large compared with the dropout
voltage. Use a series input resistor to drop
excessive voltage, and distribute the heat between
this resistor and the regulator. The low dropout
properties of Super
beta
PNP regulators allow
significant reductions in regulator power dissipation
and the associated heat sink without compromising
performance. When this technique is employed, a
capacitor of at least 1.0µF is needed directly
between the input and regulator ground.
Output Capacitor
125°C and
q
CS
is between 0°C and
V
IN
GM66500 - X.X
V
IN
V
OUT
V
OUT
GND
+
C
IN
+
C
OUT
Figure 10. Capacitor Requirements
Thermal Design
Linear regulators are simple to use. The most
complicated design parameters to consider are thermal
characteristics.
Thermal design requires four application-specific
parameters:
Maximum ambient temperature (T
A
)
Output Current (I
OUT
)
Output Voltage (V
OUT
)
Input Voltage (V
IN
)
Ground Current (I
GND
)
GM66500 SERIES
The GM66500 series requires an output capacitor to
maintain stability and improve transient response.
Proper capacitor selection is important to ensure
proper operation. The GM66500 series output
capacitor selection is dependent upon the ESR
(equivalent series resistance) of the output capacitor
to maintain stability. When the output capacitor is
47µF or greater, the output capacitor should have
less than 1W of ESR. This will improve transient
response as well as promote stability. Ultra-low-ESR
capacitors, such as ceramic chip capacitors may
promote instability. These very low ESR levels may
cause an oscillation and/or underdamped transient
response. When larger capacitors are used, the
ESR requirement approaches zero. A 100µF
ceramic capacitor can be used on the output while
maintaining stability. A low-ESR 47µF solid tantalum
capacitor works extremely well and provides good
transient response and stability over temperature.
Aluminum electrolytics can also be used, as long as
the ESR of the capacitor is 1W .
The value of the output capacitor can be increased
without limit. Higher capacitance values help to
improve transient response, ripple rejection, and
reduce output noise.
6
GAMMA [ GAMMA MICROELECTRONICS INC. ]
