G9612 Datasheet, PDF (7/8 Pages) Global Mixed-mode Technology Inc – Low-Dropout, 500mA Linear Regulator with Reset

Global Mixed-mode Technology Inc.
G9612
Foldback Current Limiting
The G9612 also include a foldback current limiter. It
monitors and controls the pass transistor’s gate volt-
age, estimating the output current and limiting it to
900mA for output voltages above 0.78V. If the output
voltage drops below 0.78V, implying a short-circuit
condition, the output current is limited to 400mA.
Thermal Overload Protection
Thermal overload protection limits total power dissipa-
tion in the G9612. When the junction temperature ex-
ceeds T_J = +160°C, the thermal sensor sends a signal
to the shutdown logic, turning off the pass transistor
and allowing the IC to cool. The thermal sensor will
turn the pass transistor on again after the IC’s junction
temperature cools by 30°C, resulting in a pulsed out-
put during thermal overload conditions.
Thermal overload protection is designed to protect the
G9612 in the event of fault conditions. For continual
operation, the absolute maximum junction temperature
rating of T_J = +160°C should not be exceeded.
The worst-case thermal resistance from junction to
air (θ_JA) requirements are:
θ_JA =
(150°C -T_A)
P_D
Use larger copper pad area to obtain specific heat sink
thermal resistance values for larger output current,
higher input-output difference, and higher ambient
temperature.
C_D Capacitor Selection
The reset timeout delay is set by internally pull-up R_D
(typical value 200kΩ) and external C_D.
When the voltage at C_D pin exceeds the buffer thresh-
old, typically 0.8 V_CC, the RESET output high. The
voltage detector and buffer have built-in hysterisis to
prevent erratic reset operation. For C_D = 0.1µF, typical
reset time delay is 30ms. The formula of delay time is:
T(ms) = 303 x C_D(µF)
Operating Region and Power Dissipation
Maximum power dissipation of the G9612 depends on
the thermal resistance of the case and circuit board,
the temperature difference between the die junction
and ambient air, and the rate of air flow. The power
dissipation across the device is P = I_OUT (V_IN-V_OUT).
The resulting maximum power dissipation is:
P_MAX=
(T_J-T_A)
(θ_JC+θ_CA)
where (T_J -T_A) is the temperature difference between
the G9612 die junction and the surrounding air, θ_JC is
the thermal resistance of the package chosen, and θ_CA
is the thermal resistance through the printed circuit
board, copper traces and other materials to the sur-
rounding air. The thermal resistance of SOT89-5 with
0.18 inch² copper heat sink isθ_JA = 125°C/W.
The power dissipation of G9612 is:
P_D = (V_IN - V_OUT) x I_OUT
Regulator Output Capacitor Selection and Regu-
lator Stability
Normally, use capacitors 0.1µF minimum on the input
and 10µF minimum on the output of the G9612. The
larger input capacitor values provide better supply noise
rejection and line-transient response. Improve load tran-
sient response, stability, and power-supply rejection by
using large output capacitors. For stable operation over
the full temperature range and with load current up to
500mA, 10µF tantalum or 47µF aluminum minimum is
recommended. Too small capacitors with small ESR
can result in oscillation.
Transient Considerations
The Typical Operating Characteristics show the
G9612 load-transient response. Two components of
the output response can be observed on the
load-transient graphs—a DC shift from the output im-
pedance due to the different load currents, and the
transient response. Typical transients for step changes
in the load current from 5mA to 500mA are 0.1V. In-
creasing the output capacitor’s value attenuates tran-
sient spikes.
Ver: 1.7
Apr 01, 2005
TEL: [phone]
http://www.gmt.com.tw
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