RT9004APQV datasheet(9/12 Pages) RICHTEK

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RT9004

Preliminary

DS9004-00 February 2008

www.richtek.com

Applications Information

Like any low-dropout regulator, the external capacitors used

with the RT9004 must be carefully selected for regulator

stability and performance. Using a capacitor whose value

is > 2.2

μF on the RT9004 input and the amount of

capacitance can be increased without limit. The input

capacitor must be located a distance of not more than

0.5 inch from the input pin of the IC and returned to a

clean analog ground. Any good quality ceramic or tantalum

can be used for this capacitor. The capacitor with larger

value and lower ESR (equivalent series resistance) provides

better PSRR and line-transient response.

The output capacitor must meet both requirements for

minimum amount of capacitance and ESR in all LDOs

application. The RT9004 is designed specifically to work

with low ESR ceramic output capacitor in space-saving

and performance consideration. Using a ceramic capacitor

whose value is at least 1

μF with ESR is > 20mΩ on the

RT9004 output ensures stability. The RT9004 still works

well with output capacitor of other types due to the wide

stable ESR range. Figure 1 shows the curves of allowable

ESR range as a function of load current for various output

capacitor values. Output capacitor of larger capacitance

can reduce noise and improve load transient response,

stability, and PSRR. The output capacitor should be located

not more than 0.5 inch from the VOUT pin of the RT9004

and returned to a clean analog ground.

Enable Function

The RT9004 features an LDO regulator enable/disable

function. To assure the LDO regulator will switch on, the

EN turn on control level must be greater than 1.2 volts.

The LDO regulator will go into the shutdown mode when

the voltage on the EN pin falls below 0.4 volts. For to

protecting the system, the RT9004 have a quick-discharge

function. If the enable function is not needed in a specific

application, it may be tied to VIN to keep the LDO

regulator in a continuously on state.

Thermal Considerations

Thermal protection limits power dissipation in RT9004.

When the operation junction temperature exceeds 165

°C,

the OTP circuit starts the thermal shutdown function and

turns the pass element off. The pass element turn on again

after the junction temperature cools by 30

°C.

RT9004 lowers its OTP trip level from 165

°C to 110°C

when output short circuit occurs (VOUT < 0.4V) as shown

in Figure 2. This limits IC case temperature under 100

°C

and provides maximum safety to end users when output

short circuit occurs.

Figure 1

Region of Stable COUT ESR vs. Load Current

0.00

0.01

0.10

1.00

10.00

100.00

100

150

200

250

300

Load Current (mA)

COUT = 1uF

Instable

Stable

100

COUT = 1

μF, X7R

Figure 2. Short Circuit Thermal Folded Back Protection

when Output Short Circuit Occurs

OUT Short to GND

0.4V

OUT

TSD

OTP Trip Point

165 C

° 110 C

110 C

80 C

IC Temperature

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