RT4723

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is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS4723-00

April

2016

12

Input Current

Inductor Current

Output Current

Time

Time

Output Ripple (ac)

DTs

I

L

V

OUT1

Figure 1. Output Ripple Voltage Without Contribution of

ESR

Under Voltage Lockout

To 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.

Soft-Start

The RT4723 employs an internal soft-start feature to

avoid high inrush current during start-up. The soft-start

function is achieved by clamping the output voltage of

the internal error amplifier with another voltage source

that is increased slowly from zero to near VIN during

the soft-start period.

Negative Output Voltage Setting

The Negative output voltage can be programmed by a

MCU through the dedicated pin according to Table 2

Shutdown Delay and Discharge

When the SWIRE signal is logic low for more than

350

s, the IC function will be shut down. The output

discharge function enabled referring to Table 3

“VOP/VON Shutdown Discharge Selection with SWIRE

Pulse

”. In shutdown mode, the input supply current for

the IC is less than 1

A.

Over Current Protection

The RT4723 includes a cycle-by-cycle current limit

function which monitors 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 RT4723 has an advanced output short-circuit

protection mechanism which prevents the IC from

damage by unexpected applications. When the output

becomes shorted to ground, and the output voltage is

under the limit level with 1ms (typ.) duration, the bias

function enters shutdown mode and can only re-start

normal operation after triggering the SWIRE pin.

Over Temperature Protection

The RT4723 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

15

C, IC will automatically resume normal operation.

To maintain continuous operation, the maximum

junction temperature should be prevented from rising

above 125

C.

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature.

The maximum power dissipation can be calculated by

the following formula :

ambient thermal resistance.

For recommended operating condition specifications,

the maximum junction temperature is 125

C. The

junction to ambient thermal resistance,

dependent.

For

WL-CSP-15B

1.39x2.07

(BSC)

package, the thermal resistance,

standard JEDEC 51-7 four-layer thermal test board.