RT6264A datasheet(21/25 Pages) RICHTEK

21 / 25 page

RT6264A/B

is a registered trademark of Richtek Technology Corporation.

DS6264A/B-02

August

2021

www.richtek.com

to improve efficiency when the input voltage is below 5.5V.

The bootstrap diode can be a low-cost one, such as

1N4148 or BAT54. The external 5V can be a fixed 5V

voltage supply from the system, or a 5V output voltage

generated by the RT6264A/B. Note that the BOOT

voltage VBOOT must be lower than 5.5V.

BOOT

0.1

μF

RT6264A/B

DBOOT

CBOOT

Figure 10. External Bootstrap Diode

External Bootstrap Resistor (Optional)

The gate driver of an internal power MOSFET, utilized

as a high-side switch, is optimized for turning on the

switch. The gate driver is not only fast enough for

reducing switching power loss, but also slow enough

for minimizing EMI. The EMI issue is worse when the

switch is turned on rapidly due to the induced high di/dt

noises. When the high-side switch is turned off, the

discharging time on SW node is relatively slow

because there’s the presence of dead time, both

high-side and low-side MOSFETs are turned off in this

interval. In some cases, it is desirable to reduce EMI

further, even at the expense of some additional power

dissipation. The turn-on rate of the high-side switch can

be slowed by placing a small bootstrap resistor RBOOT

between the BOOT pin and the external bootstrap

capacitor as shown in Figure 11. The recommended

range for the RBOOT is several ohms to 47 ohms, and it

could be 0402 or 0603 in size.

This will slow down the rates of the high-side switch

turn on and the rise of VSW. In order to improve EMI

performance

and

enhancement

the

internal

MOSFET switch, the recommended application circuit

is shown in Figure 12, which includes an external

bootstrap diode for charging the bootstrap capacitor

and a bootstrap resistor RBOOT placed between the

BOOT pin and the capacitor/diode connection.

BOOT

CBOOT

RT6264A/B

RBOOT

0.1

μF

Figure 11. External Bootstrap Resistor at the BOOT

BOOT

0.1

μF

RT6264A/B

RBOOT

DBOOT

CBOOT

Figure12. External Bootstrap Diode and Resistor at

the BOOT Pin

Thermal Considerations

In many applications, the RT6264A/B does not

generate much heat due to its high efficiency and low

thermal resistance of its TSOT-23-6 (FC) package.

However, in applications which the RT6264A/B runs at

a high ambient temperature and high input voltage, the

generated heat may exceed the maximum junction

temperature of the part.

The RT6264A/B includes an over-temperature protection

(OTP) circuitry to prevent overheating due to excessive

power dissipation. If the junction temperature reaches

approximately 155°C, the RT6264A/B stops switching

the power MOSFETs until the temperature is cooled

down by 35°C.

Note that the over-temperature protection is intended to

protect

the

device

during

momentary

overload

conditions. The protection is activated outside of the

absolute maximum range of operation as a secondary

fail-safe and therefore should not be relied upon

operationally.

Continuous

operation

above

the

specified

absolute

maximum

operating

junction

temperature

may

impair

device

reliability

permanently damage the device.

The maximum power dissipation can be calculated by

the following formula :

















D MAX

J MAX

JA EFFECTIVE

= T



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