RT6296B
Application Information
The RT6296B 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 2A.
5V
BOOT
RT6296B
SW
100nF
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
External Soft-Start Capacitor
R5
R1
R2
FB
RT6296B
GND
V
OUT
RT6296B 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 (CSS) between SS pin and GND. The Chip
provides a 11A charge current (ISS) for the external
capacitor. The soft-start time (tSS, VREF is from 0V to
0.8V) can be calculated by the following formula :
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
R2
VOUT VFB 1
C
(nF)1.3
(A)
SS
t
(ms) =
SS
I
SS
Where VFB is the feedback reference voltage (0.807V
typ.). Table 1 lists the recommended resistors value for
common output voltages.
Inductor Selection
The inductor value and operating frequency determine
the ripple current according to a specific input and
output voltage. The ripple current IL increases with
higher VIN and decreases with higher inductance.
Table 2. Recommended Resistors Value
VOUT (V)
1.0
R1 (k)
20.5
R2 (k)
84.5
R5 (k)
82
3.3
40.2
13
33
V
V
OUT
OUT
I
1
L
5.0
40.2
7.68
33
f L
V
IN
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output
voltage ripple. High frequency with small ripple current
can achieve highest efficiency operation. However, it
requires a large inductor to achieve this goal.
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 RT6296B.
For the ripple current selection, the value of IL =
0.3(IMAX) will be a reasonable starting point. The
largest ripple current occurs at the highest VIN. To
guarantee that the ripple current stays below the
specified maximum, the inductor value should be
chosen according to the following equation :
VOUT
VOUT
IN(MAX)
V
L
1
f IL(MAX)
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
10
DS6296B-02 June 2016
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
