ISSUED DATE :2005/12/12
REVISED DATE :
Ordering Information ( contd. )
The GQ2181 series of COMS regulators contain a PMOS pass transistor, voltage reference, error amplifier,
over-current protection, and thermal shutdown.
The P-channel pass transistor receives data from the error amplifier, over-current shutdown, and thermal
protection circuits. During normal operation, the error amplifier compares the output voltage to a precision
reference. Over-current and Thermal shutdown circuits become active when the junction temperature exceeds
150 , or the current exceeds 150mA. During thermal shutdown, the output voltage remains low. Normal
operation is restored when the junction temperature drops below 120 .
The GQ2181 switches from voltage mode to current mode when the load exceeds the rated output current.
This prevents over-stress. The GQ2181 also incorporates current fold-back to reduce power dissipation when
the output is short circuited. This feature becomes active when the output drops below 0.8 volts, and reduces
the current flow by 65%. Full current is restored when the voltage exceeds 0.8 volts.
The GQ2181 is stable with an output capacitance to ground of 0.22 F or greater. Ceramic capacitors have the
lowest ESR, and will offer the best AC performance. Conversely, Aluminum Electrolytic capacitors exhibit the
highest ESR, resulting in the poorest AC response.
A second capacitor is recommended between the input and ground to stabilize Vin. The input capacitor should
be at least 1 F to have a beneficial effect.
A large capacitor improves the AC ripple rejection, but also makes the output come up slowly. This “Soft”
turn-on is desirable in some applications to limit turn-on surges.
All capacitors should be placed in close proximity to the pins. A “Quiet” ground termination is desirable. This
can be achieved with a “Star” connection.
When actively, pulled low, the PMOS pass transistor shuts off, and all internal circuits are powered down. In
this state, the quiescent current is less than 1 A. This pin behaves much like an electronic switch.