CMOS LOW DROPOUT REGULATORS

2007-5-18

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FSP2114

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

The FSP2114 is a high performance LDO with low quiescent current consumption. As illustrated in the above Figure,

Functional Block Diagram, the FSP2114 architecture incorporates reference and bias circuitry, error amplifier,

feedback voltage resistor divider, 2Ω P-channel power MOSFET pass transistor and current limiter.

VOLTAGE REGULATION

Normally, the LDO's error amplifier compares the output feedback voltage (via the resistor divider) with the reference

voltage and generates an error signal that is used to drive the P-channel power MOSFET. When the output voltage

is higher than the needed value, the P-channel is driven to maintain regulation. When the output voltage is lower

than the needed value, the P-channel conducts to increase the output to its desired value. This negative feedback

mechanism results in a constant regulated output voltage.

CURRENT LIMIT

When the output current is at the current limit value, the current limiter circuitry prevents the output current from

increasing further. This current limit value is typically 400mA for output voltage higher than 2V, and decreases for

lower output voltage parts (see Typical Performance Characteristics). As the output voltage decreases, the current

limit value folds back gradually, eventually reaching 100mA at 0V.

APPLICATION INFORMATION

INPUT CAPACITOR

Any good quality capacitor with a value of 1µF or more can be used as an input capacitor for this LDO. Connect the

input capacitor as close to the IN and G as possible. Ceramic capacitors have better performance and lower ESR

(Equivalent Series Resistance) than other types of capacitors, and are recommended.

OUTPUT CAPACITOR

The FSP2114 LDO requires an output capacitor for stability. This capacitor should be connected as close to OUT

and G as possible to maximize the performance of the device. The output capacitance and ESR ranges for stability

However, to ensure the best performance for the device, the output capacitor should have a minimum capacitance of

1µF, and an ESR value between 10mΩ and 500mΩ. High quality ceramic capacitors with X7R or X5R dielectric

types are strongly recommended.

IN

G

THERMAL

SHUTDOWN

REFERENCE

& BIAS

OUT

CURRENT

SENSE