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G923 Schematic ( PDF Datasheet ) - Interpoint Corporation Company

Teilenummer G923
Beschreibung High PSRR LDO Regulators
Hersteller Interpoint Corporation Company
Logo Interpoint Corporation Company Logo 




Gesamt 9 Seiten
G923 Datasheet, Funktion
www.DataSheet4U.com
Global Mixed-mode Technology Inc.
G923
300mA High PSRR LDO Regulators
Features
„ Low, 90µA No-Load Supply Current
„ Guaranteed 300mA Output Current
„ Dropout Voltage is 200mV @ 150mA Load
„ PSRR=65dB @ 120Hz
„ Over-Temperature Protection and Short-Circuit
Protection
„ Two Modes of Operation ----
Fixed Mode: 1.50V~5.00V
Adjustable Mode: from 1.25V to 5.50V
„ Max. Supply Current in Shutdown Mode < 1µA
„ Low Output Noise at 224µVRMS
„ Stable with low cost ceramic capacitors
Applications
„ Notebook Computers
„ Cellular Phones
„ PDAs
„ Digital still Camera and Video Recorders
„ Hand-Held Devices
„ Audio Codec
General Description
The G923 is a low supply current, high PSRR, and low
dropout linear regulator that comes in a space saving
SOT-23-5 package. The supply current at no-load is
90µA. In the shutdown mode, the maximum supply
current is less than 1µA. Operating voltage range of
the G923 is from 2.50V to 5.50V. The over-current
protection limit is set at 550mA typical. An over- tem-
perature protection circuit is built-in in the G923 to
prevent thermal overload. These power saving fea-
tures make the G923 ideal for use in the bat-
tery-powered applications such as notebook com-
puters, cellular phones, and PDAs.
The G923 has two modes of operation. When the SET
pin is connected to ground, its output is a pre-set value:
1.50V~5.00V. There is no external component needed
to decide the output voltage. When an output other
than the preset value is needed, two external resistors
should be used as a voltage divider. The output volt-
age is then decided by the resistor ratio. The G923
comes in a space saving SOT-23-5 package.
Pin Configuration
SHDN 1
5 SET
GND 2
G923
G963
IN 3
SOT-23-5
4 OUT
CIN
_ 1µF
BATTERY
IN OUT
G923
SHDN
GND
SET
Fixed mode
OUTPUT
VOLTAGE
COUT
1µF
BATTERY C1µINF
IN OUT
G923
SET
SHDN
GND
R1
R2
OUTPUT
VOLTAGE
1CµOFUT
Adjustable mode
Ver: 1.1
Jan 19, 2006
TEL: 886-3-5788833
http://www.gmt.com.tw
1






G923 Datasheet, Funktion
Global Mixed-mode Technology Inc.
Pin Description
G923
PIN NAME
FUNCTION
Active-Low Shutdown Input. A logic low reduces the supply current to less than 1µA. Connect to IN for normal opera-
1 SHDN
tion.
Ground. This pin also functions as a heatsink. Solder to large pads or the circuit board ground plane to maxi-
2 GND
mize thermal dissipation.
3 IN Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with 1µF to GND
Regulator Output. Fixed or adjustable from 1.25V to +5.5V. Sources up to 300mA. Bypass with a 1µF, 0.2Ω
4 OUT
typical ESR capacitor to GND.
Feedback Input for Setting the Output Voltage. Connect to GND to set the output voltage to the preset output
5 SET
voltage. Connect to an external resistor divider for adjustable-output operation.
Detailed Description
The block diagram of the G923 is shown in Figure 1. It
consists of an error amplifier, 1.25V bandgap reference,
PMOS output transistor, internal feedback voltage divider,
mode comparator, shutdown logic, over current protec-
tion circuit, and over temperature protection circuit.
The mode comparator compares the SET pin voltage
with an internal 350mV reference. If the SET pin volt-
age is less than 350mV, the internal feedback voltage
divider’s central tap is connected to the non-inverting
input of the error amplifier. The error amplifier com-
pares non-inverting input with the 1.25V bandgap ref-
erence. If the feedback voltage is higher than 1.25V,
the error amplifiers output becomes higher so that the
PMOS output transistor has a smaller gate-to-source
voltage (VGS). This reduces the current carrying capa-
bility of the PMOS output transistor, as a result the
output voltage decreases until the feedback voltage is
equal to 1.25V. Similarly, when the feedback voltage is
less than 1.25V, the error amplifier causes the output
PMOS to source more current to pull the feedback
voltage up to 1.25V. Thus, through this feedback ac-
tion, the error amplifier, output PMOS, and the voltage
dividers effectively form a unity-gain amplifier with the
feedback voltage force to be the same as the 1.25V
bandgap reference. The output voltage, VOUT, is then
given by the following equation:
VOUT = 1.25 (1 + R1/R2).
(1)
Alternatively, the relationship between R1 and R2 is
given by:
R1 = R2 (VOUT /1.25 - 1).
(2)
For the reasons of reducing power dissipation and
loop stability, R2 is chosen to be 100KΩ. For G923-
330, R1 is 164K, and the pre-set VOUT is 3.30V.
When external voltage divider is used, as shown in
Figure 2, the SET pin voltage will be larger than
350mV. The non-inverting input of the amplifier will be
connected to the external voltage divider. However,
the operation of the feedback loop is the same, so that
the conditions of Equations 1 and 2 are still true. The
output voltage is still given by Equation 1.
IN
SHDN
GND
Ver: 1.1
Jan 19, 2006
SHUTDOWN
LOGIC
ERROR
AMP
OVER CURRENT
PROTECT & DYNAMIC
FEEDBACK
OVER TEMP.
PROTECT
1.25V
Vref
MODE COMPARATOR
350mV
P
OUT
SET
R1
R2
Figure 1. Functional Diagram
6
TEL: 886-3-5788833
http://www.gmt.com.tw

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