RT4730 datasheet(13/17 Pages) RICHTEK

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RT4730

DS4730-01

March 2017

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Application Information

The RT4730 is a highly integrated power solution with

Buck-Boost and inverting charge pump to generate positive

and negative output voltage for AMOLED bias. The Buck-

Boost DC-DC converter can operate with wide input voltage

from 2.9V to 4.8V. The converter feedback loop is internally

compensated for both Buck and Boost operation and it

provides seamless transition between Buck and Boost

modes operation.

Input Capacitor Selection

PVIN input ceramic capacitor with 4.7

μF capacitance and

AVIN input ceramic capacitor with 10

μF capacitance is

suggested for applications. For better voltage filtering,

select ceramic capacitors with low ESR, X5R and X7R

types are suitable because of their voltage and temperature

ranges.

Inductor Selection

The recommended power inductor is 1

μH. In applications,

need to select an inductor with the low DCR to provide

good performance and efficiency.

Output Capacitor Selection

The output capacitor selection determines the output

voltage ripple and transient response. It is recommended

to use ceramic capacitors placed as close as possible to

output and GND pins of the IC.

Under Voltage Lockout

The prevent abnormal operation of the IC in low voltage

condition, an under voltage lockout is included which shuts

down IC operation when input voltage is lower than the

specified threshold voltage.

Positive and Negative Output Voltage Setting

The positive and negative output voltage can be

programmed by a MCU through the dedicated pin

according to SWIRE pulse.

Over Current Protection

The RT4730 includes a cycle-by-cycle current limit function

which monitor the inductor current during each ON period.

The power switch will be forced off to avoid large current

damage once the current is over the limit level.

Short Circuit Protection

The RT4730 has an advanced output short-circuit protection

mechanism which prevents the IC from damage by

unexpected application. When the output becomes

shorted to ground, and the output voltage is under the

limit level, the IC enters shutdown mode and can only re-

start normal operation after re-power on.

Over Temperature Protection

The RT4730 equips an over temperature protection circuitry

to prevent overheating due to excessive power dissipation.

The OTP will shut down the bias operation when ambient

temperature exceeds 140

°C. Once the ambient

temperature cools down by approximately 10

°C, IC will

automatically resume normal operation. To maintain

continuous operation, the maximum junction temperature

should be prevented from rising above 130

°C.

Thermal Considerations

The junction temperature should never exceed the

absolute maximum junction temperature TJ(MAX), listed

under Absolute Maximum Ratings, to avoid permanent

damage to the device. The maximum allowable power

dissipation depends on the thermal resistance of the IC

package, the PCB layout, the rate of surrounding airflow,

and the difference between the junction and ambient

temperatures. The maximum power dissipation can be

calculated using the following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA

where TJ(MAX) is the maximum junction temperature, TAis

the ambient temperature, and

θJA is the junction-to-ambient

thermal resistance.

For continuous operation, the maximum operating junction

temperature indicated under Recommended Operating

Conditions is 125

°C. The junction-to-ambient thermal

resistance,

θJA, is highly package dependent. For a WL-

CSP-16B 2.34 x 2.34 (BSC), the thermal resistance,

θJA,

is 42.3

°C/W on a standard JEDEC 51-7 high effective-

thermal-conductivity four-layer test board. The maximum

power dissipation at TA = 25

°C can be calculated as below :

PD(MAX) = (125

°C − 25°C) / (42.3°C/W) = 2.36W for a

WL-CSP-16B 2.34 x 2.34 (BSC) package.

RT4730 Datasheet(PDF) 13 Page - Richtek Technology Corporation

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