G914 Datasheet, PDF (4/6 Pages) Global Mixed-mode Technology Inc – 150mA Low-Dropout Linear Regulators

Global Mixed-mode Technology Inc.
G914
IN
OUT
＋
－ _BATTERY ^CIN
1µF
G914
ADJ
SHDN
GND
OUTPUT
VOLTAGE
R1
R2
C_OUT
R_L
1µF
470pF
of the chosen package to the ambient air. In the case
of a SOT23-5 package, the thermal resistance is typi-
cally 220^oC/Watt.
The die attachment area of the G914’s lead frame is
connected to pin 2, which is the GND pin. Therefore,
the GND pin of G914 can carry away the heat of the
G914 die very effectively. To improve the power dis-
sipation, 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 G914 use a current mirror to monitor the output
current. A small portion of the PMOS output transis-
tor’s current is mirrored onto a resistor such that the
voltage across this resistor is proportional to the out-
put current. This voltage is compared against the ref-
erence voltage. Once the output current exceeds the
limit, the PMOS output transistor enters constant cur-
rent mode. The current is set to 370mA typically.
Over Temperature Protection
To prevent abnormal temperature from occurring, the
G914 has a built-in temperature monitoring circuit.
When it detects the temperature is above 150^oC, the
output transistor is turned off. When the IC is cooled
down to below 135^oC, the output is turned on again. In
this way, the G914 will be protected against abnormal
junction temperature during operation.
Shutdown Mode
When the SHDN pin is connected a logic low voltage,
the G914 enters shutdown mode. All the analog cir-
cuits are turned off completely, which reduces the
current consumption to only the leakage current. The
output is disconnected from the input. When the out-
put has no load at all, the output voltage will be dis-
charged to ground through the internal resistor voltage
divider.
Operating Region and Power Dissipation
Since the G914 is a linear regulator, its power dissipa-
tion is always given by P = I_OUT (V_IN – V_OUT). The
maximum power dissipation is given by:
P_D(MAX) = (T_J–T_A)/θ_JA,=150^oC-25^oC/220^oC/W= 568mW
Applications Information
Capacitor Selection and Regulator Stability
Normally, use a 1µF capacitor on the input and a 1µF
capacitor on the output of the G914. Larger input ca-
pacitor values and lower ESR provide better sup-
ply-noise rejection and transient response. A higher-
value input capacitor (10µF) may be necessary if large,
fast transients are anticipated and the device is lo-
cated several inches from the power source.
Power-Supply Rejection and Operation from Sources
Other than Batteries
The G914 is designed to deliver low dropout voltages
and low quiescent currents in battery powered sys-
tems. Power-supply rejection is 42dB at low frequen-
cies.
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 G914 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 0mA to 100mA is
12mV. Increasing the output capacitor's value and
decreasing its ESR attenuates transient spikes.
Input-Output (Dropout) Voltage
A regulator's minimum input-output voltage differential
(or dropout voltage) determines the lowest usable
supply voltage. In battery-powered systems, this will
determine the useful end-of-life battery voltage. Be-
cause the G914 use a P-channel MOSFET pass tran-
sistor, their dropout voltage is a function of R_DS(ON)
multiplied by the load current.
Where (T_J–T_A) is the temperature difference the G914
die and the ambient air,θ_JA, is the thermal resistance
Ver 0.1 Preliminary
Nov 05, 2001
TEL: [phone]
http://www.gmt.com.tw
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