rt9259c Richtek Technology Corporation, rt9259c Datasheet - Page 8

• Manufacturer Part Number: rt9259c
• Description: Synchronous Buck Dc-dc Linear Power Controller
• Manufacturer: Richtek Technology Corporation

RT9259C
Application Information
Introduction
The RT9259C is a
specifically designed to deliver high quality power where
12V power source is available. This part consists of a
synchronous buck controller and an LDO controller. The
synchronous buck controller integrates internal MOSFET
drivers that support 12V+12V bootstrapped voltage for high
efficiency power conversion. The bootstrap diode is built-
in to simplify the circuit design and minimize external part
count. The LDO controller drives an external N-MOSFET
for lower power requirement.
Internal 5VDD Regulator
It is highly recommended to power
decoupled 12V to VCC12 pin. VCC12 powers the RT9259C
control circuit, low side gate driver and bootstrap circuit for
high side gate driver. A bootstrap diode is embedded to
facilitates PCB design and reduce the total BOM cost. No
external Schottky diode is required. The RT9259C
integrates MOSFET gate drives that are powered from the
VCC12 pin and support 12V + 12V driving capability.
Converters that consist of RT9259C feature high efficiency
without special consideration on
MOSFETs.
An internal linear regulator regulates VCC12 input to a
5VDD voltage for internal control logic circuit. No external
bypass capacitor is required for filtering the 5VDD voltage.
This further facilitates PCB design and reduces the total
BOM cost.
Power On Reset
The RT9259C
power (at the VCC12) pin. The power on reset function
(POR) continually monitors the input bias supply voltage
at the VCC12 pin. The VCC12V POR level is typically
9.6V at VCC12V rising.
Frequency Setting and Shut Down
Connecting a resistor R
sets the operation frequency. The relation can be roughly
expressed in the equation.
www.richtek.com
8
f
OSC
≅
2
30
kHz
automatically
+
7700
R
dual-channel DC/DC controller
RT
RT
(kHz)
from the RT_DIS pin to GND
initializes upon applying input
the RT9259C with well-
the selection of
When let open, the free running frequency is 230kHz
typically. Figure 1 shows the operation frequency vs. R
for quick reference.
Shorting the RT_DIS pin to GND with an external signal-
level MOSFET shuts down the device. This allows flexible
power sequence control for specified application. The
RT_DIS pin threshold voltage is 0.4V typically.
VIN1 Detection
The RT9259C continuously generates a 10kHz pulse train
with 1μs pulse width to turn on the upper MOSFET for
detecting the existence of VIN1 after VCC12V POR and
RT_DIS enabled as shown in Figure 2. PHASE pin voltage
is monitored during the detection duration.
If the PHASE voltage crosses 1.5V four times, VIN1
existence is recognized and the RT9259C
start cycle as described in next section.
V
IN1
PHASE_M
1400
1200
1000
POR_H
800
600
400
200
0
10
Figure 1. RT vs. fsw at Low Frequency
+
-
1.5V
Figure 2
Internal Counter will count (V
four times (rising & falling) to recognize
V
1st 2nd 3rd 4th PHASE
IN1
R
RT
is ready.
UGATE
PHASE
DS9259C-03 August 2007
100
(kohm)
(kΩ)
waveform
initiates its soft
PHASE
1000
> 1.5V)
RT