Revision 1, May 2002 www.gammamicro.com
0.8A PRECISION LINEAR REGULATORS
GM1117
PRELIMINARY
1
Adjustable or Fixed Output
Output Current of 0.8A
Dropout Voltage (typical) 1.0V @ 0.8A
Line Regulation 0.2% max.
Load Regulation 0.4% max.
Fast Transient Response
Current Limit Protection
Thermal Shutdown Protection
The GM1117 series of positive adjustable and fixed
regulators are designed to provide 0.8A output with
low dropout voltage performance. On-chip trimming
adjusts the reference voltage to 1%. Put them to work
in post regulators or microprocessor power supplies
where low voltage operation and fast transient
response are required.
Pin-to-pin compatible with the LT1086 family of
regulators, the GM1117's are available in surface-
mount SOT-223 and TO-252 packages.
3
2
1
VIN
VOUT
GND*
SOT-223
CONNECTION DIAGRAMS
Applications:
High Efficiency Linear Regulators
Post Regulators for Switching Supplies
Microprocessor Supply
Hard Drive Controllers
Battery Chargers
* On fixed versions Pin1=GND,
on adjustable versions Pin1=ADJ
V
OUT
GND
V
IN
3.3V @ 0.8A
22
F
5.0V
10
F
5.0V
GM1117-3.3
TYPICAL APPLICATION CIRCUITS
(Fixed Version)
(
Adjustable
Version)
V
OUT
ADJ
V
IN
3.3V @ 0.8A
22
F
5.0V
10
F
5.0V
GM1117-A
5.0V
0.1
F
5.0V
Tant
200
1.0%
124
1.0%
3
2
1
VIN
VOUT
ADJ*
SOT-223
(Top View)
(Top View)
ADJ/GND*
TO-252 (D-PAK)
3
2
1
V
IN
V
OUT
(Top View)
Revision 1, May 2002 www.gammamicro.com
0.8A PRECISION LINEAR REGULATORS
GM1117
PRELIMINARY
3
7
1
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V
IN
V
OUT
ADJ
Thermal
Shutdown
Bandgap
Reference
Output
Current
Limit
Error
Amplifier
+
-
BLOCK DIAGRAM
(
Adjustable
Version)
ORDERING INFORMATION
Note: other fixed versions are available: V
OUT
= 1.5V to 5.0V
Revision 1, May 2002 www.gammamicro.com
0.8A PRECISION LINEAR REGULATORS
GM1117
PRELIMINARY
4
ELECTRICAL CHARACTERISTICS
Unless otherwise specified: Adjustable Option: V
IN
= 2.65V to 7.0V and I
O
= 10mA to I
RATED
. Fixed Options:
I
O
= 0mA to I
RATED
, V
IN
(2.5V) = 3.9V to 7.0V, V
IN
(2.85V) = 4.25V to 7.0V, V
IN
(3.3V) = 4.75V to 7.0V.
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NOTES:
(1) Low duty cycle pulse testing with Kelvin connections required
(2)
V
OUT
,
V
REF
= 1%
(3) Bandwidth of 10 Hz to 10 kHz
(4) 120Hz input ripple (C
ADJ
for ADJ = 25
F)
(5) O.T. = over specified operating junction temperature range
Revision 1, May 2002 www.gammamicro.com
0.8A PRECISION LINEAR REGULATORS
GM1117
PRELIMINARY
5
The GM117 series linear regulators provide fixed and
adjustable output voltages at currents up to 0.8A. These
regulators are protected against overcurrent conditions
and include thermal shutdown protection. The GM117's
have a composite PNPNPN output transistor and
require an output capacitor for stability.
A detailed procedure for selecting this capacitor follows.
APPLICATIONS INFORMATION
Stability Considerations
The output compensation capacitor helps to determine
three main characteristics of a linear regulator's
performance: startup delay, load transient response,
and loop stability. The capacitor value and type is based
on cost, availability, size and temperature constraints. A
tantalum or aluminum electrolytic capacitor is preferred,
as a film or ceramic capacitor with almost zero ESR
can cause instability. An aluminum electrolytic capacitor
is the least expensive type, but when the circuit operates
at low temperatures, both the value and ESR of the
capacitor will vary widely. For optimum performance over
the full operating temperature range, a tantalum
capacitor is best. A 22
F tantalum capacitor will work
fine in most applications, but with high current regulators
such as the GM117 higher capacitance values will
improve the transient response and stability. Most
applications for the GM117's involve large changes in
load current, so the output capacitor must supply
instantaneous load current. The ESR of the output
capacitor causes an immediate drop in output voltage
given by:
In microprocessor applications an output capacitor
network of several tantalum and ceramic capacitors in
parallel is commonly used. This reduces overall ESR
and minimizes the instantaneous output voltage drop
under transient load conditions. The output capacitor
network should be placed as close to the load as
possible for the best results.
V =
I x ESR
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 output capacitor
will discharge into the output of the regulator. The
discharge current depends on the value of capacitor,
output voltage and rate at which V
IN
drops.
In the GM117 linear regulators, the discharge path is
through a large junction, and protection diodes are
normally not needed. However, if the regulator is used
with large output capacitance values and the input
voltage is instantaneously shorted to ground, damage
can occur. In this case, a diode connected as shown
above in Figure 1.
V
OUT
GND
V
IN
GM1117-3.3
V
OUT
V
IN
C1
C2
IN4002
V
OUT
ADJ
V
IN
GM1117-A
V
OUT
V
IN
C1
C2
IN4002
R1
R2
C
ADJ
(a) Fixed Version
(b) Adjustable Version
FIGURE 1
(a),(b)
Protection Diode Scheme for
Large Output Capacitors
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