RT2810A/B
R
100k
External BOOT Bootstrap Diode
EN
V
EN
RT2810A/B
GND
IN
When the input voltage is lower than 5.5V it is
recommended to add an external bootstrap diode between
VIN(or VINR) and the BOOT pin to improve enhancement
of the internal MOSFET switch and improve efficiency.
The bootstrap diode can be a low cost one such as 1N4148
or BAT54.
Q1
Enable
Figure 3. Digital Enable Control Circuit
R
EN1
External BOOT Capacitor Series Resistance
V
IN
EN
The internal power MOSFET switch gate driver is
optimized to turn the switch on fast enough for low power
loss and good efficiency, but also slow enough to reduce
EMI. Switch turn-on is when most EMI occurs since VSW
rises rapidly. 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 (<47Ω)
resistance between BOOT and the external bootstrap
capacitor. This will slow the high-side switch turn-on and
VSW's rise. To remove the resistor from the capacitor
charging path (avoiding poor enhancement due to
undercharging the BOOT capacitor), use the external diode
shown in Figure 6 to charge the BOOT capacitor and place
the resistance between BOOT and the capacitor/diode
R
EN2
RT2810A/B
GND
Figure 4. ResistorDivider for Lockout Threshold Setting
Output Voltage Setting
Set the desired output voltage using a resistive divider
from the output to ground with the midpoint connected to
FB. The output voltage is set according to the following
equation :
VOUT = 0.7 x (1 + R1 / R2)
V
OUT
R1
FB
RT2810A/B
R2
connection.
GND
5V
Figure 5. Output Voltage Setting
BOOT
Place the FB resistors within 5mm of the FB pin. Choose
R2 between 10kΩ and 100kΩ to minimize power
consumption without excessive noise pick-up and
calculate R1 as follows :
RT2810A/B
SW
0.1µF
Figure 6. External Bootstrap Diode
PVCC Capacitor Selection
R2(V
0.7)
OUT
R1
0.7
For output voltage accuracy, use divider resistors with 1%
or better tolerance.
Decouple PVCC to GND with a 1μF ceramic capacitor.
High grade dielectric (X7R, or X5R) ceramic capacitors
are recommended for their stable temperature and bias
voltage characteristics.
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2810A/B-07 April 2019
www.richtek.com
13
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
