Application Notes

The LP8358 is a linear regulator with power good output

designed to be used with a low ESR, low cost ceramic

capacitors.

EXTERNAL CAPACITORS

The LP8358 regulator requires an output capacitor to main-

tain stability. The capacitor must be at least 1µF or greater.

The capacitor can be low-ESR ceramic chip capacitor, how-

ever for improved capacitance over temperature, tantalum

capacitors can be used.

A 1µF input capacitor is recommend when the supply capaci-

tance is more than 10 inches away from the device, or when

the supply is a battery.

X7R dielectric ceramic capacitors are recommended be-

cause of their temperature performance. X7R-type capacitor

change capacitance by 15% over their operating tempera-

ture range and are the most stable type of ceramic capaci-

tors. Z5U and Y5V dielectric capacitors change value by as

much 50% and 60% respectively over their operating tem-

perature range. To use a ceramic chip capacitor with Y5V

dielectric, the value must be much higher than a X7/R ce-

ramic or a tantalum capacitor to ensure the same minimum

capacitance value over the operating temperature range.

Tantalum capacitors have a very stable dielectric (10% over

their operating temperature range) and can also be used

with this device.

ENABLE/SHUTDOWN

The LP8358 has an active high enable pin that allows the

to the Shutdown pin will cause the output to turn off, in this

state current consumed by the regulator goes nearly to zero.

voltage. The enable/shutdown pin must not be left floating; a

floating enable pin may cause an indeterminate state on the

output.

ACTIVE SHUTDOWN

The LP8358 is designed with a N-channel MOSFET that

acts as a shutdown clamp. The N-channel turns on when the

device is disabled to allow the output capacitor and load to

discharge

POWER GOOD

The power good output is an open-drain output with extreme

low R

reset generator once the regulated voltage is up and/ or a

fault condition. When a fault condition occurs, the output of

the power good pin goes low. The power good output comes

back up once the output has reached 97% of its nominal

value and 1ms to 5ms delay has passed , see timing dia-

gram.

The LP8358 internal circuit monitors overcurrent, tempera-

ture and falling output voltage. If one of these conditions is

flagged this indicates a fault condition.

The flagged condition output is fed into an onchip delay

circuit that drives the open drain output transistor.

TRANSIENT RESPONSE

The LP8358 implements a unique output stage to dramati-

cally improve transient response recovery time. The output is

a totem-pole configuration with a P-channel MOSFET pass

device and a N-channel MOSFET clamp. The N-channel

clamp is a significantly smaller device that prevents the

output voltage from overshooting when a heavy load is

removed. This feature helps to speed up the transient re-

sponse by significantly decreasing transient response recov-

ery time during the transition from heavy load to light load.

THERMAL BEHAVIOR

The LP8358 regulator has internal thermal shutdown to pro-

tect the device from over heating. Under all operating con-

ditions, the maximum junction temperature of the LP8358

must be below 125˚C. Maximum power dissipation can be

calculated based on the output current and the voltage drop

across the part. The maximum power dissipation is

P

θ

JA

θ

for the LP8358 in the SOT23-5 package. T

ambient temperature T

perature of the die, 125˚C.

When operating the LP8358 at room temperature, the maxi-

mum power dissipation is 425mW.

The actual power dissipated by the regulator is

P

Substituting P

for the operating condition that is critical to the application

will give the maximum operating condition for the regulator

circuit. To prevent the device from entering thermal shut-

down, maximum power dissipation cannot be exceeded.

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