RT8293AHZSP Просмотр технического описания (PDF) - Richtek Technology
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RT8293AHZSP Datasheet PDF : 15 Pages
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RT8293A
Application Information
The RT8293A is a synchronous high voltage buck converter
that can support the input voltage range from 4.5V to 23V
and the output current can be up to 3A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
Soft-Start
The RT8293A 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.).
VOUT
Chip Enable Operation
R1
The EN pin is the chip enable input. Pulling the EN pin
FB
low (<0.4V) will shut down the device. During shutdown
RT8293A
R2
mode, the RT8293A quiescent current drops to lower than
GND
3µA. Driving the EN pin high (>2.7V, < 5.5V) will turn on
the device again. For external timing control (e.g.RC),
Figure 1. Output Voltage Setting
the EN pin can also be externally pulled high by adding a
The output voltage is set by an external resistive voltage
divider according to the following equation :
REN* resistor and CEN* capacitor from the VIN pin (see
Figure 5).
VOUT
=
VFB
1+
R1
R2
An external MOSFET can be added to implement digital
control on the EN pin when no system voltage above 2.5V
where VFB is the feedback reference voltage (0.8V typ.).
is available, as shown in Figure 3. In this case, a 100kΩ
pull-up resistor, REN, is connected between VIN and the
External Bootstrap Diode
Connect a 100nF low ESR ceramic capacitor between
EN pin. MOSFET Q1 will be under logic control to pull
down the EN pin.
the BOOT pin and SW pin. This capacitor provides the
gate driver voltage for the high side MOSFET.
VIN
It is recommended to add an external bootstrap diode
between an external 5V and BOOT pin for efficiency Chip Enable
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 of the
REN
100k
2 VIN
BOOT 1
CIN
RT8293A
7 EN
SW 3
CBOOT
L
Q1
8 SS
CSS
4,
9 (Exposed Pad)
GND
FB 5
COMP 6
CC RC
CP
VOUT
R1 COUT
R2
RT8293A. Note that the external boot voltage must be
lower than 5.5V.
Figure 3. Enable Control Circuit for Logic Control with
5V
Low Voltage
BOOT
RT8293A
SW
100nF
Figure 2. External Bootstrap Diode
To prevent enabling circuit when VIN is smaller than the
VOUT target value, a resistive voltage divider can be placed
between the input voltage and ground and connected to
the EN pin to adjust IC lockout threshold, as shown in
Figure 4. For example, if an 8V output voltage is regulated
from a 12V input voltage, the resistor, REN2, can be
selected to set input lockout threshold larger than 8V.
DS8293A-03 March 2011
www.richtek.com
9
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