RT6296E
Application Information
The RT6296E is a high voltage buck converter that can
support the input voltage range from 4.5V to 17V and the
input voltage range from 4.5V to 17V and the output current
can be up to 3A.
Output Voltage Selection
The resistive voltage divider allows the FB pin to sense a
fraction of the output voltage as shown in Figure 1.
Figure 2. External Bootstrap Diode
FB
RT6296E
GND
R5
R1
V
OUT
R2
BOOT
RT6296E
SW
100nF
5V
The TTH Voltage setting
The TTH voltage is used to be change the transition
threshold between power saving mode and CCM. Higher
TTH voltage gets higher efficiency at light load condition
but larger output ripple; a lower TTH voltage can improve
output ripple but degrades efficiency during light load
condition. A resistor divider from PVCC (5V) of RT6296E
can help to build TTH voltage, as shown in Figure 3. It is
recommended that TTH voltage should be less than 0.6V.
PVCC
R3
TTH
RT6296E
GND
R4
Figure 1. Output Voltage Setting
For adjustable voltage mode, the output voltage is set by
an external resistive voltage divider according to the
following equation :
R1
V
OUT
�½
V
FB
1
R2
Where V
FB
is the feedback reference voltage (0.807V typ.).
Table 2 lists the recommended resistors value for common
output voltages.
Table 2. Recommended Resistors Value
V
OUT
(V)
1.0
3.3
5.0
R1 (k)
20.5
40.2
40.2
R2 (k)
84.5
13
7.68
R5 (k)
49.9
8.2
8.2
Figure 3. TTH Voltage Setting
External Soft-Start Capacitor
RT6296E provides external soft-start function. The soft-
start function is used to prevent large inrush current while
converter is being powered-up. The soft-start timing can
be programmed by the external capacitor (C
SS
) between
SS pin and GND. The Chip provides a 11μA charge current
(I
SS
) for the external capacitor. The soft-start time (t
SS
,
V
REF
is from 0V to 0.8V) can be calculated by the following
formula :
t
SS
(ms) =
C
SS
(nF)
1.3
I
SS
(
A)
External Bootstrap Diode
Connect a 100nF low ESR ceramic capacitor between
the BOOT pin and SW pin. 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, as shown as Figure 2, for
efficiency improvement when input voltage is lower than
5.5V or duty ratio is higher than 65% .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 (PVCC) of the RT6296E.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6296E-02
June 2016
www.richtek.com
9
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
