RT8299 查看數據表（PDF） - Richtek Technology
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RT8299 Datasheet PDF : 15 Pages
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RT8299
Application Information
The RT8299 is a synchronous high voltage buck converter
that can support the input voltage range from 3V to 24V
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.
VOUT
R1
FB
RT8299
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
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
RT8299. Note that the external boot voltage must be lower
than 5.5V
5V
BOOT
RT8299
SW
100nF
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 RT8299 quiescent current drops to lower than
3μA. Driving the EN pin high (>2V, < 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 from 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 100kΩ
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
REN
100k
Q1
VIN
BOOT
CIN
RT8299
SW
EN
VCC
FB
C
PGOOD
GND
CBOOT
L
R
100k
VCC
VOUT
R1 COUT
R2
Figure 3. Enable Control Circuit for Logic Control with
Low Voltage
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.
VIN
12V
VIN
BOOT
REN
CIN
10µF
RT8299
100k
SW
EN
CBOOT
L
VOUT
8V
REN2
R1 COUT
VCC
C
FB
R
100k
R2
GND PGOOD
VCC
Figure 2. External Bootstrap Diode
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8299-01 May 2012
Figure 4. The Resistors can be Selected to Set IC
Lockout Threshold
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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