Global Mixed-mode Technology Inc.
OUTPUT
VOLTAGE
IN
＋
－
BATTERY C
IN
1µF
OUT
R1
G923
G923
SHDN
GND
SET
R2
C
OUT
4.7µF
R
L
mount device, heat sinking is accomplished by using
the heat spreading capabilities of the PC board and its
copper traces. In the case of a SOT-23-5 package, the
thermal resistance is typically 240
°
C/Watt. (See
Recommended Minimum Footprint) [Figure 3] Refer to
Figure 4 is the G923 valid operating region (Safe Op-
erating Area) & refer to Figure 5 is maximum power
dissipation of SOT-23-5.
The die attachment area of the G923
’
s lead frame is
connected to pin 2, which is the GND pin. Therefore,
the GND pin of G923 can carry away the heat of the
G923 die very effectively. To improve the maximum
power providing capability, connect the GND pin to
ground using a large ground plane near the GND pin.
Figure 2. Adjustable Output Using External
Feedback Resistors
Over Current Protection
The G923 uses a current sense-resistor to monitor the
output current. A portion of the PMOS output transis-
tor’s current is mirrored to a resistor such that the
voltage across this resistor is proportional to the output
current. Once the output current exceeds limit thresh-
old, G923 would be protected with a limited output
current. Further more, when the output is short to
ground, the output current would be folded-back to a
less limit.
Over Temperature Protection
To prevent abnormal temperature from occurring, the
G923 has a built-in temperature monitoring circuit.
When it detects the temperature is above 145
°
C, the
output transistor is turned off. When the IC is cooled
down to below 120
°
C, the output is turned on again. In
this way, the G923 will be protected against abnormal
junction temperature during operation.
Shutdown Mode
When the
SHDN
pin is connected a logic low voltage,
the G923 enters shutdown mode. All the analog cir-
cuits are turned off completely, which reduces the
current consumption to only the leakage current. The
G923 output pass transistor would get into high im-
pedance level. There is an internal discharge path to
help to shorten discharge delay time.
Operating Region and Power Dissipation
Since the G923 is a linear regulator, its power dissipa-
tion is always given by P = I
OUT
(V
IN
- V
OUT
). The maxi-
mum power dissipation is given by:
Applications Information
Capacitor Selection and Regulator Stability
Normally, use a 1
µ
F capacitor on the input and a
4.7
µ
F capacitor on the output of the G923. Larger in-
put capacitor values and lower ESR provide better
supply-noise rejection and transient response. A
higher- value input capacitor (10
µ
F) may be necessary
if large, fast transients are anticipated and the device
is located several inches from the power source.
Power-Supply Rejection and Operation from
Sources Other than Batteries
The G923 is designed to deliver low dropout voltages
and low quiescent currents in battery powered sys-
tems. Power-supply rejection is 65dB at low frequen-
cies. As the frequency increases above 20kHz, the
output capacitor is the major contributor to the rejec-
tion of power-supply noise.
When operating from sources other than batteries,
improve supply-noise rejection and transient response
by increasing the values of the input and output ca-
pacitors, and using passive filtering techniques.
Load Transient Considerations
The G923 load-transient response graphs show two
components of the output response: a DC shift of the
output voltage due to the different load currents, and
the transient response. Typical overshoot for step
changes in the load current from 10mA to 300mA is
8mV. Increasing the output capacitor's value and de-
creasing its ESR attenuates transient spikes.
Input-Output (Dropout) Voltage
A regulator
'
s minimum input-output voltage differential
(or dropout voltage) determines the lowest usable sup-
ply voltage. In battery-powered systems, this will de-
termine the useful end-of-life battery voltage. Because
the G923 use a P-channel MOSFET pass transistor,
their dropout voltage is a function of R
DS(ON)
multiplied
by the load current.
P
D(MAX)
= (T
J
- T
A
) /
θ
JA
,=(150
°
C-25
°
C)/240
°
C/W = 520mW
Where (T
J
-T
A
) is the temperature difference the G923
die and the ambient air,
θ
JA
, is the thermal resistance
of the chosen package to the ambient air. For surface
Ver: 1.5
Jan 16, 2007
TEL: 886-3-5788833
http://www.gmt.com.tw
7
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
