RT6203E
The amplitude of the capacitive soar is a function of the
load step, the output capacitor value, the inductor value
R
EN1
V
IN
EN
R
EN2
RT6203E
GND
and the output voltage :
2
L(I
)
OUT
V
SOAR
=
2C
V
OUT
OUT
Figure 4. ResistorDivider for Lockout Threshold Setting
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.
External Bootstrap Diode
Connect a 0.1μF 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
RT6203ENote that the external boot voltage must be lower
than 5.5V.
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 ENpin 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 ENvoltage
as the additional input under voltage lockout function, as
shown in Figure 4.
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 (<47Ω)
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.
R
EN
V
IN
EN
RT6203E
C
EN
GND
Figure 2. Enable Timing Control
R
EN
V
IN
EN
RT6203E
Q1
Enable
GND
Figure 3. Logic Control for the EN Pin
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
16
DS6203E-00 January 2019
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
