RT6203ENGSP datasheet(16/21 Pages) RICHTEK

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RT6203E

DS6203E-00 January 2019

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

The amplitude of the capacitive soar is a function of the

load step, the output capacitor value, the inductor value

and the output voltage :

OUT

SOAR

OUT

L( I

)





Due to some modern digital loads can exhibit nearly

instantaneous load changes, the amplitude of the ESR

step up or down should be taken into consideration.

Enable Operation (EN)

EN is a high voltage input pin. For automatic start-up, the

EN pin can be connected to VIN directly. The inherent

hysteresis makes EN useful as a simple timing delay. To

add an additional time delay, the EN pin can be connected

to GND through a capacitor CEN, as shown in Figure 2.

The additional time delay for switching operation to start

can be calculated with the EN's internal logic threshold.

(typically 2V).

An external MOSFET can be added to implement an logic-

controlled EN pin, as shown in Figure 3. The MOSFET

Q1 can provide the logic control on the EN pin, pulling it

down. To prevent enabling circuit when VIN is smaller than

the VOUT target value or some other desired voltage level,

a resistive divider can be placed to control the EN voltage

as the additional input under voltage lockout function, as

shown in Figure 4.

Figure 2. Enable Timing Control

Figure 3. Logic Control for the EN Pin

RT6203E

GND

VIN

REN1

REN2

External Bootstrap Diode

Connect a 0.1

μF low ESR ceramic capacitor between the

BOOT and SW pins. This capacitor provides the gate driver

voltage for the high-side MOSFET. It is recommended to

add an external bootstrap diode between an external 5V

and BOOT pin for efficiency improvement when input

voltage is lower than 5.5V. The bootstrap diode can be a

low cost one such as IN4148 or BAT54. The external 5V

can be a 5V fixed input from system or a 5V output of the

RT6203E Note that the external boot voltage must be lower

than 5.5V.

External BOOT Capacitor Series Resistor

The internal power MOSFET gate driver is not only

optimized to turn the switch on fast enough to minimize

switching loss, but also slow enough to reduce EMI. Since

the switch rapidly turn-on will induce high di/dt noise which

let EMI issue much worse. During switch turn-off, SW is

discharged relatively slowly by the inductor current during

the dead time between high-side and low-side switch on-

times. In some cases it is desirable to reduce EMI further,

at the expense of some additional power dissipation. The

switch turn-on can be slowed by placing a small (<47

Ω)

resistance between BOOT and the external bootstrap

capacitor. This will slow the high-side switch turn-on speed

and VSW's rise. The recommended external diode

connection is shown in Figure 5, using external diode to

charge the BOOT capacitor, and place a resistor between

BOOT and the capacitor/diode connection to reduce turn-

on speed for any EMI issue consideration.

GND

VIN

REN

CEN

RT6203E

GND

VIN

REN

Enable

Figure 4. Resistor Divider for Lockout Threshold Setting

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