RT9012 datasheet(9/11 Pages) RICHTEK

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RT9012

Preliminary

DS9012-06 August 2007

www.richtek.com

Applications Information

Like any low-dropout regulator, the external capacitors used

with the RT9012 must be carefully selected for regulator

stability and performance. Using a capacitor whose value

is > 1

μF on the RT9012 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 RT9012 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

RT9012 output ensures stability. The RT9012 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 RT9012

and returned to a clean analog ground.

Figure 1. Stable Cout ESR Range

Thermal Considerations

Thermal protection limits power dissipation in RT9012.

When the operation junction temperature exceeds 170

°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 40

°C. RT9012

lowers its OTP trip level from 170

°C to 110°C when output

short circuit occurs (VOUT < 0.4V) as shown in Figure 2. It

limits IC case temperature under 100

°C and provides

maximum safety to customer while output short circuit

occurring.

OUT Short to GND

0.4V

OUT

TSD

OTP Trip Point

170 C

° 110 C

110 C

80 C

IC Temperature

Figure 2. Short Circuit Thermal Folded Back Protection

when Output Short Circuit Occurs (Patent)

For continuous operation, do not exceed absolute

maximum operation junction temperature 125

°C. The

power dissipation definition in device is :

PD = (VIN

− VOUT) x IOUT + VIN x IQ

The maximum power dissipation depends on the thermal

resistance of IC package, PCB layout, the rate of

surroundings airflow and temperature difference between

junction to ambient. The maximum power dissipation can

be calculated by following formula :

PD(MAX) = ( TJ(MAX)

− TA ) /θJA

Where TJ(MAX) is the maximum operation junction

temperature 125

°C, TAis the ambient temperature and the

θJA is the junction to ambient thermal resistance.

Region of Stable COUT ESR vs. Load Current

0.001

0.01

0.1

100

150

200

250

300

Load Current (mA)

Unstable Range

Stable Range

Simulation Verify

RT9012-FM, VIN = 5V

CIN = COUT1 =

COUT2 = 1uF/X7R

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