rt9259 Richtek Technology Corporation, rt9259 Datasheet - Page 8

• Manufacturer Part Number: rt9259
• Description: Synchronous Buck Dc-dc Linear Power Controller
• Manufacturer: Richtek Technology Corporation

RT9259
Application Information
Introduction
The RT9259 is a dual-channel DC/DC controller 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 the RT9259 with well-
decoupled 12V to VCC12 pin. VCC12 powers the RT9259
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 RT9259 integrates
MOSFET gate drives that are powered from the VCC12
pin and support 12V + 12V driving capability. Converters
that consist of RT9259 feature high efficiency without
special consideration on the selection of 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 RT9259 automatically
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
+
7700
R
RT
RT
(kHz)
from the RT_DIS pin to GND
initializes upon applying input
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 RT9259 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 RT9259 initiates its soft
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
DS9259-03T00 August 2007
is ready.
UGATE
PHASE
100
(kohm)
(kΩ)
waveform
PHASE
1000
> 1.5V)
RT