A5268完整版

3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
Maximum
-0.3V to +30V -1V to VIN+0.3 -0.3V to VSW + 6 -0.3V to +6 -0.3V to VIN 2 200
Unit
V V V V V kV
n Applications
l Distributed Power System l Networking System l FPGA, DSP, ASIC Power Supplies l Notebook Computers
C
n Typical Application
VIN 12V R4 100K Ω IN
mW
Maximum Junction Temperature
150
o
C
Solder Iron(10 Sec)**
350
* Measure θJC on backside center of Exposed Pad. ** MIL-STD-202G 210F
6
Rev.B.02
A5268
n Electrical Specifications
Unit
o
C C C
o
C
-65 to +150
o
ie
Rev.B.02
5
A5268
n Thermal Information
Parameter
Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation
2
IN
3 4 5
SW GND FB
6
COMP
7
EN
8
SS
4
Rev.B.02
A5268
n Absolute Maximum Ratings
Parameter
Supply Voltage Switch Voltage Boost Switch Voltage All Other Pins EN Voltage ESD Classification (HBM) ESD Classification (MM)
3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
Package
SOP-8/PP
Die Attach
Symbol
θJC
Maximum
19
Unit
o
C/W
SOP-8/PP
Conductive Epoxy
θJA PD
84
SOP-8/PP
1450
2
Rev.B.02
A5268
n Pin Configuration
SOP-8/PP Top View
8 7 6 5
3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
A5268 1. BS 2. IN 3. SW
A5268
4. GND 5. FB 6. COMP 7. EN Die Attach: Conductive Epoxy 8. SS
A5268
n General Description
The A5268 is a fixed frequency monolithic synchronous buck regulator that accepts input voltage from 4.75V to 28V. Two NMOS switches with low on-resistance are integrated on the die. Current mode topology is used for fast transient response and good loop stability. Shutdown mode reduces the input supply current to less than 1µA. An adjustable soft-start prevents inrush current at turn-on. This device is available in SOP-8/PP package with exposed pad for low thermal resistance.
VIN = 12V, TA = 25OC, unless otherwise noted.
Parameter Shutdown Current Supply Current Feedback Voltage OVP Threshold Voltage Error Amplifier Voltage Gain Error Amplifier Transconductance High-side Switch On Resistance Low-side Switch On Resistance Switch Leakage Current High-side Switch Current Limit Low-side Switch Current Limit COMP to Current Sense Transconductance Current Limit Oscillation Frequency Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum On Time Input Undervoltage Lockout Input Undervoltage Lockout Hysteresis Soft-Start Current Source Soft-Start Period EN Lockout Threshold Voltage GCS fOSC,CL fOSC,SCR DMAX t ON,MIN VUVLO VUVLO,HYST ISS t SS V EN A EA GEA RDS,ON,HI RDS,ON,LO ISW,LK V FB Symbol ISHDN
n Functional Block Diagram
1.1V OVDET OVP
3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
CURRENT SENSE AMP FB 0.3V osc CLK BS S Q COMP 6uA 0.925V EA CLAMP ML SS OVP OTP UVP OTDET UVLO IRCMP GND EN 2.5V 1.5V LOCKOUT CMP SHUTDOWN CMP INTERNAL REGULATORS IN PWM R LOGIC MH SW SLOPE 5V VIN
EN BS SW
ie
C5 10nF VOUT 5V 3A
C1 10µ F/35V x2
L1 15µH/3.4A
A5268
SS GND FB S COMP
C4 0.1µ F
C3 3.3nF
R3 6.98KΩ1%
R1 44.2K Ω1% R2 10KΩ1%
C2 22µF/10V x2
Rev.B.02
1
A5268
Pin Name
BS
Pin Description
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side NChannel MOSFET switch. Connect a 10nF or greater capacitor from SW to BS to power the high side switch. Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 4.75V to 28V power source. Bypass IN 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 BS to power the high-side switch. Ground. Connect the exposed pad to pin 4. Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback reference voltage is 0.925V. 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 2.7V to turn on the regulator, drive it lower than 1.1V to turn it off. Pull up to the IN pin with 100KΩ resister for automatic start up. Soft-start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. Add a 0.1µF capacitor set the soft-start period to 15mS. To disable the soft start feature, leave the SS unconnected.
1
2
3
4
Note: The area enclosed by dashed line represents Exposed Pad and connect to.02
3
A5268
n Pin Description
Pin Number
1
3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
3A, 28V, 340KHz Synchronous Rectified Step-Down Converter
n Features
l 3A Output Current l Wide 4.75V to 28V Operating Input Range l Integrated Power MOSFET Switches l Output Adjustable from 0.925V to 25V l Up to 95% Efficiency l Programmable Soft Start l Stable with Low ESR Ceramic Output Capacitors l Cycle-by Cycle Over Current Protection l Fixed 340KHz Frequency l Input Under Voltage Lockout l System Protected by Over-current Limiting, Over-voltage Protection and Thermal Shutdown l Thermally Enhanced SOP-8/PP Package l Green Products Meet RoHS Standards
v
n Recommended Operating Conditions
Parameter
Ambient Temperature Range Junction Temperature Range Storage Temperature Range
Rating
-40 to +85 -40 to +125