RT8296BHGSP Ver la hoja de datos (PDF) - Richtek Technology
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RT8296BHGSP Datasheet PDF : 15 Pages
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RT8296B
Application Information
The RT8296B is a synchronous high voltage buck converter
that can support an input voltage range from 4.5V to 23V
and the output current can be up to 3A.
Output Voltage Setting
The resistive voltage divider allows the FB pin to sense
the output voltage as shown in Figure 1.
VOUT
R1
FB
RT8296B
R2
GND
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive voltage
divider according to the following equation :
VOUT
=
VFB
1+
R1
R2
where VFB is the feedback reference voltage (0.8V typ.).
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 for efficiency
improvement when input voltage is lower than 5.5V or duty
cycle 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 of the
RT8296B. Note that the external boot voltage must be
lower than 5.5V.
5V
BOOT
RT8296B
SW
100nF
Figure 2. External Bootstrap Diode
Soft-Start
The RT8296B contains an external soft-start clamp that
gradually raises the output voltage. The soft-start timing
can be programmed by the external capacitor between
SS pin and GND. The chip provides a 6µA charge current
for the external capacitor. If 0.1µF capacitor is used to
set the soft-start, the period will be 13.5ms(typ.).
Chip Enable Operation
The EN pin is the chip enable input. Pulling the EN pin
low (<0.4V) will shutdown the device. During shutdown
mode, the RT8296B quiescent current will drop below 3µA.
Driving the EN pin high (>2.7V, < 5.5V) will turn on the
device again. For external timing control (e.g.RC), the EN
pin can also be externally pulled high by adding a REN*
resistor and CEN* capacitor f rom the VIN pin
(see Figure 5).
An external MOSFET can be added to implement digital
control on the EN pin when no system voltage above 2.5V
is available, as shown in Figure 3. In this case, a 100 kΩ
pull-up resistor, REN, is connected between VIN and the
EN pin. MOSFET Q1 will be under logic control to pull
down the EN pin.
VIN
Chip Enable
2 VIN
BOOT 1
REN
CIN
RT8296B
100k
SW 3
7 EN
Q1
8 SS
CSS
4,
9 (Exposed Pad) GND
FB 5
COMP 6
CBOOT L
VOUT
R1
COUT
CC RC
R2
CP
Figure 3. Enable Control Circuit for Logic Control with Low Voltage
DS8296B-03 March 2011
www.richtek.com
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