RT8230A datasheet(4/18 Pages) RICHTEK

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RT8237E

DS8237E-02

October 2020

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Operation

The RT8237E integrates a Constant-On-Time (COT) PWM

controller, and the controller provides the PWM signal

which relies on the output ripple voltage comparing with

internal reference voltage.

The UGATE driver is turned on at the beginning of each

cycle. After the internal one-shot timer expires, the UGATE

driver will be turned off. The pulse width of this one-shot is

determined by the converter's input voltage and the output

voltage to keep the frequency fairly constant over the input

voltage and output voltage range.

Power On Reset, UVLO

Power On Reset (POR) occurs when VCC rises above to

approximately 4.1V (typical), the RT8237E will reset the

fault latch and prepare the PWM for operation. When the

input voltage below 3.7V(min), the Under Voltage Lockout

(UVLO) circuitry inhibits switching by keeping UGATE and

LGATE low.

Soft-Start

The output voltage will track the internal ramp voltage during

soft-start interval to prevent large inrush current and output

voltage overshoot while the converter is being powered

up.

Mode Selection

The RT8237E supports mode selection through the RF

by connecting a resistor from the RF pin to either GND or

PGOOD. When the resistor is connected to GND, the

controller operates in diode emulation mode. When the

resistor is connected to PGOOD, the controller operates

in CCM mode.

Current Limit Setting

The RT8237E has a cycle-by-cycle current limit control.

The current limit circuit employs a unique

“valley” current

sensing algorithm. If the magnitude of the sensing signal

at PHASE is above the current limit threshold, the PWM

is not allowed to initiate a new cycle.

Over Voltage Protection

The output voltage can be continuously monitored for over

voltage condition. When the output voltage exceeds 25%

of its set voltage threshold, the UGATE goes low and the

LGATE is forced high.

Under Voltage Protection

The output voltage can be continuously monitored for under

voltage condition. When the output voltage is less than

70% of its set voltage, under voltage protection is triggered

and then both UGATE and LGATE gate drivers are forced

low.

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