Document
RT9226
March, 2000
PWM Step-down DC/DC Converter Controller
General Description
Features
The RT9226 is a low cost, high-efficiency voltage-mode PWM controller for motherboard power supply application. High-side N-channel MOSFET driver, short-circuit protection, and soft start function are integrated in a single chip. A simple high power buck regulator with shutdown function can be implemented with minimum external components.
The RT9226 provides current-limit protection by monitoring the voltage drop across N-channel MOSFET in over current condition, therefore, eliminates the current sensing resistor and minimizes the efficiency loss. The soft start function reduces the stress on power supply and components in power on duration. The 200 kHz operating frequency and high speed PWM control loop with high-side N-channel MOSFET driver provide optimized compromise between efficiency, cost, and response speed.
l Low cost and small size l High efficiency l Fast response with 200kHz operating frequency l Adjustable current limit by sensing MOSFET
rDS(ON), without extra current sensing resistor l Shutdown function
Applications
l Low cost CPU power supply l Motherboard I/O power supply l Add-on card power supply
Ordering Information
RT9226-oo
Pin Configurations
Part Number
Pin Configuration
Package type S: SOP-14
Operation temperature range C: Commercial standard
RT9226CS (Plastic SOP-14)
TOP VIEW
RT 1
14 VCC
OCSET 2
13 NC
SS 3
12 NC
NC 4
11 NC
FB 5
10 BOOT
EN 6
9 UGATE
GND 7
8 PHASE
RichTek Technology Corp.
6F, No. 35, Hsintai Road, Chupei City, Hsinchu, Taiwan, R.O.C. -- 1 / 6 --
DS9226-01 Tel: (8863)5510047 Fax: (8863)5537749
Absolute Maximum Ratings
l Supply Voltage (VCC) l Input, Output or I/O Voltage
l Ambient Temperature Range(TA) l Operating Junction Temperature Range (TJ) l Storage Temperature Range (TSTG) l Power Dissipation and Thermal Characteristics:
l SOP Plastic Package, PD @ TA=25 l Thermal Resistance, R JA l Lead Temperature (Soldering) 10 seconds (TLEAD)
Electrical Characteristics
Vcc=12V, GND=0V, TA=25 , unless other wise specified.
Parameter
Symbol
Test condition
VCC Supply Current Nominal Supply Current Power-on Reset
ICC
UGATE Open
VCC Rising Threshold VCC Falling Threshold Enable Input Threshold
VOCSET = 4.5V VOCSET = 4.5V
Oscillator
Frequency
Ramp Amplitude
Internal Voltage Reference
Reference Voltage
VREF
PWM Controller Error Amplifier
DC Gain
PWM Controller Gate Driver
UGATE Source UGATE Sink Protection
RUGATE RUGATE
IUGATE = 0.3A IUGATE = 0.3A
OCSET Sink Current SS Current
IOCSET ISS
VOCSET = 4.5V VSS = 1.5V
RT9226
March, 2000
15V GND–0.3V to Vcc+0.3V 0 to 70 0 to 125 −65 to 150
0.625W 160 /W 260
Min Typ Max Units -- 3 -- mA
-- 9.5 --- 7.5 -0.2 -- 2.2
V V V
170 200 230 kHz
-- 1.9 --
--
1.225 1.250 1.275 V
-- 65 -- dB
-- 8 --- 6 --
170 200 230 -- 10 --
µA µA
RichTek Technology Corp.
6F, No. 35, Hsintai Road, Chupei City, Hsinchu, Taiwan, R.O.C. -- 2 / 6 --
DS9226-01 Tel: (8863)5510047 Fax: (8863)5537749
Function Block Diagram
EN
10µA SS Soft Start
4.5V
Power-on Reset
_ +
PWM
Control
+ Comparator Logic
Over Current Comparator
Vref _+
+
FB _
Error
Amp
Oscillator
RT
RT9226
March, 2000
VCC OCSET 200µA
PHASE
BOOT UGATE GND
RichTek Technology Corp.
6F, No. 35, Hsintai Road, Chupei City, Hsinchu, Taiwan, R.O.C. -- 3 / 6 --
DS9226-01 Tel: (8863)5510047 Fax: (8863)5537749
Pin Description
Pin No. Pin Name
1 RT
2 OCSET 3 SS 4 NC 5 FB 6 EN 7 GND 8 PHASE 9 UGATE 10 BOOT 11 NC 12 NC 13 NC 14 VCC
RT9226
March, 2000
Pin Function
Oscillator frequency adjusting pin
The switching frequency (f) is increased by placing a resistor (R) from this pin to GND and reduced by placing a resistor (R) to VCC according to following formulae:
Speed up: f = 200(1+ 2 × 10 4 ) kHz R
1
Speed down: f = 200(1–
) kHz
6 × 10− 6 R
Current limit set pin with 200µA current sink Soft start pin, connect a capacitor from this pin to GND No connected Voltage-control feedback loop input Regulator enable pin Ground pin Current limit sense pin MOSFET driver output Driver power No connected No connected No connected IC power
RichTek Technology Corp.
6F, No. 35, Hsintai Road, Chupei City, Hsinchu, Taiwan, R.O.C. -- 4 / 6 --
DS9226-01 Tel: (8863)5510047 Fax: (8863)5537749
Typical Applications
RT9226
March, 2000
R1 C3
12V
10Ω C1 1µF
D2 15V
10
1000 pF
L1
BOOT
2
14 VCC
OCSET
R4 2.2k
+ 1µH C4
1 RT
9
1000µF x 2
6 EN
UGATE
CET6030L
Q1
L2
38
C2 0.1µ F
SS 5
FB
PHASE 7
GND
D1
7µ H C5
+
1000µF x 6
RT9226
R2
330 R3 200
VIN 5V
V OUT 3.3V/10A
C4, C5: Each 1000µF 6.3WV DC, Sanyo MV-GX or Equivalent. L1: Core: Micrometals T50-52; Winding: 5 turns of 18 AWG. L2: Core: Micrometals T60-52; Winding: 14 turns of 17 AWG. D1: BYV118
Q1: CET6030L
RichTek Technology Corp.
6F, No. 35, Hsintai Road, Chupei City, Hsinchu, Taiwan, R.O.C. -- 5 / 6 --
DS9226-01 Tel: (8863)5510047 Fax: (8863)5537749
Package Information
RT9226
March, 2000
14 8.