ISSUED DATE :2004/12/28
REVISED DATE :2006/04/18B
GTM
CORPORATION
Detailed Description
The GJ2148 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
150к, or the current exceeds 2.2A. During thermal shutdown, the output voltage remains low. Normal
operation is restored when the junction temperature drops below 120к.
The GJ2148 behaves like a current source when the load reaches 2.2A. However, if the load impedance drops
below 0.3ꢂ, the current drops back to 600mA to prevent excessive power dissipation. Normal operation is
restored when the load resistance exceeds 0.75ꢂ.
External Capacitors
The GJ2148 is stable with an output capacitance to ground of 4.7ꢀF 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. Unfortunately, large value ceramic capacitors are
comparatively expensive. One option is to parallel a 0.1ꢀF ceramic capacitor with a 10ꢀF Aluminum Electrolytic.
The benefit is low ESR, high capacitance, and low overall cost.
A second capacitor is recommended between the input and ground to stabilize Vin. The input capacitor should
be at least 0.1ꢀF to have a beneficial effect.
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.
Characteristics Curve
GJ2148
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