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SS8014-xxG

Over Current Protection

The SS8014 uses a current mirror to monitor the output

current. A small portion of the PMOS output transistor’s

current is mirrored onto a resistor such that the voltage

across this resistor is proportional to the output current.

This voltage is compared against the 1.25V reference.

Once the output current exceeds the limit, the PMOS

output transistor is turned off. Once the output transistor is

turned off, the current monitoring voltage decreases to

zero, and the output PMOS is turned on again. If the over

current condition persist, the over current protection cir-

cuit will be triggered again. Thus, when the output is

shorted to ground, the output current will be alternating

between 0 and the over current limit. The typical over

current limit of the SS8014 is set to 350mA. Note that

the input bypass capacitor of 1µF must be used in this

case to filter out the input voltage spike caused by the

surge current due to the inductive effect of the package

pin and the printed circuit board’s routing wire. Otherwise,

the actual voltage at the IN pin may exceed the absolute

maximum rating.

Over Temperature Protection

To prevent abnormal temperature from occurring, the

SS8014 has a built-in temperature monitoring circuit.

When it detects the temperature is above 150

output transistor is turned off. When the IC is cooled

down to below 135

this way, the SS8014 will be protected against abnor-

mal junction temperature during operation.

Shutdown Mode

When the SHDN pin is connected a logic low voltage,

the SS8014 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 output has no load

at all, the output voltage will be discharged to ground

through the internal resistor voltage divider.

Operating Region and Power Dissipation

Since the SS8014 is a linear regulator, its power dissi-

maximum power dissipation is given by:

SS8014 die and the ambient air, and

θ

resistance of the chosen package to the ambient air. For

surface mount devices, heat sinking is accomplished by

using the heat spreading capabilities of the PC board and

its copper traces. In the case of a SOT23-5 package, the

thermal resistance is typically 240

ommended Minimum Footprint) [Figure 2]. Refer to Fig-

ure 3 for the SS8014 valid operating region (Safe Op-

erating Area) & refer to Figure 4 for the maximum power

dissipation of the SOT-23-5.

The die attachment area of the SS8014’s lead frame is

connected to pin 2, which is the GND pin. Therefore, the

GND pin of SS8014 can carry away the heat of the

SS8014 die very effectively. To improve the power

dissipation, connect the GND pin to ground using a large

ground plane near the GND pin.

Applications Information

Capacitor Selection and Regulator Stability

Normally, use a 1µF capacitor on the input and a 1µF

capacitor on the output of the SS8014. Larger input

capacitor 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 located

several inches from the power source. For stable opera-

tion over the full temperature range, with load currents up

to 120mA, a minimum of 1µF is recommended.

Power-Supply

Rejection

and

Operation

from

Sources Other than Batteries

The SS8014 is designed to deliver low dropout volt-

ages and low quiescent currents in battery powered sys-

tems. Power-supply rejection is 57dB at low frequencies

as the frequency increases above 20 kHz; the output

capacitor is the major contributor to the rejection of

power-supply noise.

When operating from sources other than batteries, im-

prove supply-noise rejection and transient response by

increasing the values of the input and output capacitors,

and using passive filtering techniques.

Load Transient Considerations

The SS8014 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 at-

tenuates 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. Because the

SS8014 uses a P-channel MOSFET pass transistor, the

load current.

1/12/2005 Rev.2.10