Document
RT8269
3A, 24V, 400kHz Step-Down Converter
General Description
The RT8269 is a high voltage buck converter that can support the input voltage range from 4.75V to 24V and the output current can be up to 3A. Current Mode operation provides fast transient response and eases loop stabilization. The chip provides protection functions such as cycle-bycycle current limiting and thermal shutdown protection. In shutdown mode, the regulator draws 25μA of supply current. The RT8269 is available in a SOP-8 (Exposed Pad) surface mount package.
Features
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Wide Operating Input Range : 4.75V to 24V Adjustable Output Voltage Range : 0.92V to 15V Output Current up to 3A 25μA Low Shutdown Current Power MOSFET : 0.1Ω High Efficiency up to 95% 400kHz Fixed Switching Frequency Stable with Low ESR Output Ceramic Capacitors Thermal Shutdown Protection Cycle-By-Cycle Over Current Protection RoHS Compliant and Halogen Free
Ordering Information
RT8269 Package Type SP : SOP-8 (Exposed Pad-Option 1) Lead Plating System G : Green (Halogen Free and Pb Free)
Note : Richtek products are :
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Applications
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Distributive Power Systems Battery Charger DSL Modems Pre-regulator for Linear Regulators
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RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
(TOP VIEW)
BOOT VIN SW GND
2 3 4 8
`
SS EN COMP FB
GND 9
7 6 5
SOP-8 (Exposed Pad)
Typical Application Circuit
VIN 4.75V to 24V Chip Enable 2 CIN 10µFx2 VIN BOOT RT8269 7 EN SW 3 1 CBOOT L1 10nF 10µH D1 B330A CC 2.7nF R1 25.8k R2 10k VOUT 3.3V/3A COUT 22µFx2
8 SS CSS 4, 0.1µF 9 (Exposed Pad) GND
FB 5 COMP 6 RC 22k
CP NC
DS8269-02 March 2011
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datasheet pdf - http://www.DataSheet4U.net/
RT8269
Table 1. Recommended Component Selection
VOUT (V) R1 (k Ω) R2 (kΩ ) R C (kΩ ) CC (nF) L ( μ H) C OUT (μ F)
15 10 8 5 3.3 2.5 1.8 1.2
153 100 77 43 25.8 17 9.1 3
10 10 10 10 10 10 10 10
62 54 40 27 22 16 13 13
0.82 1.2 1.5 2.2 2.7 2.2 2.2 2.2
22 22 15 15 10 6.8 4.7 2.2
22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2
Functional Pin Description
Pin No. 1 Pin Name BOOT Pin Function High Side Gate Drive Boost Input. BOOT supplies the drive for the high side N-MOSFET switch. Connect a 10nF or greater capacitor from SW to BOOT to power the high side switch. Power Input. VIN supplies the power to the IC, as well as the step-down converter switches. Bypass VIN to GND with a suitable large capacitor to eliminate noise on the input to the IC. Power Switching Output. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high side switch.
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2
VIN
3 4, 9 (Exposed Pad) 5
SW GND FB
Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Feedback Input. FB senses the output voltage to regulate said voltage. The feedback reference voltage is 0.92V typically. Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off. If the EN pin is open, it will be pulled to high by internal circuit. Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1μF capacitor sets the soft-start period to 10ms.
6
COMP
7
EN
8
SS
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DS8269-02 March 2011
datasheet pdf - http://www.DataSheet4U.net/
RT8269
Function Block Diagram
VIN VCC 1µA EN 10k 1.1V 3V VA + Shutdown Comparator 0.5V VCC Foldback Control + + Current Comparator Logic Internal Regulator Oscillator 400kHz/120kHz Current Sense Slope Comp Amplifier + -
VA
BOOT SW
VCC 10µA
UV Comparator
GND
SS
+ +EA Gm = 680µA/V
0.92V
FB
COMP
Absolute Maximum Ratings
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(Note 1)
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Supply Voltage, VIN ----------------------------------------------------------------------------------------- −0.3V to 26V Switching Voltage, SW ------------------------------------------------------------------------------------- −0.3V to (VIN + 0.3V) BOOT Voltage ------------------------------------------------------------------------------------------------ (VSW − 0.3V) to (VSW + 6V) The Other Pins ----------------------------------------------------------------------------------------------- −0.3V to 6V Power Dissipation, PD @ TA = 25°C SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------- 1.333W Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA ----------------------------------------------------------.