G914X(2002) 查看數據表（PDF） - Global Mixed-mode Technology Inc
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G914X Datasheet PDF : 10 Pages
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Global Mixed-mode Technology Inc.
G914X
Pin Description
PIN
NAME
FUNCTION
1
IN
Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with 1µF to GND.
2
GND
Ground. This pin also functions as a heatsink. Solder to large pads or the circuit board ground
plane to maximize thermal dissipation.
3
SHDN
Active-High Enable Input. A logic low reduces the supply current to less than 1µA. Connect to IN for
normal operation.
4
BYP
This is a reference bypass pin. It should connect external 10nF capacitor to GND to reduce out-
put noise. Bypass capacitor must be no less than 1nF. (CBYP≥ 1nF)
5
OUT
Regulator Output. Sources up to 150mA. Bypass with a 1µF, ＜0.2Ω typical ESR capacitor to
GND.
Detailed Description
The block diagram of the G914X is shown in Figure 1.
It consists of an error amplifier, 1.25V bandgap refer-
ence, PMOS output transistor, internal feedback volt-
age divider, shutdown logic, over current protection
circuit, and over temperature protection circuit.
The internal feedback voltage divider’s central tap is
connected to the non-inverting input of the error ampli-
fier. The error amplifier compares non-inverting input
with the 1.25V bandgap reference. If the feedback
voltage is higher than 1.25V, the error amplifier’s out-
put becomes higher so that the PMOS output transis-
tor has a smaller gate-to-source voltage (VGS). This
reduces the current carrying capability of the PMOS
output transistor, as a result the output voltage de-
creases 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
conduct more current to pull the feedback voltage up
to 1.25V. Thus, through this feedback action, the error
amplifier, output PMOS, and the voltage divider effec-
tively 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 output voltage versions of G914X, the output
voltages are 2.7V for G914A, 2.8V for G914B, 3.0V for
G914C, 3.3V for G914D, and 2.5V for G914E, 2.85V
for G914F, 1.50V for G914G and 1.80V for G914H.
IN
SHDN
SHUTDOWN
LOGIC
－
ERROR
AMP
＋
OVER CURRENT
PROTECT & DYNAMIC
FEEDBACK
GND
OVER TEMP.
PROTECT
1.25V
Vref
Figure 1. Functional Diagram
OUT
BYP
R1
R2
CBYP
Ver: 1.2
Jun 30, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
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