40V, 3A, 500KHz DC/DC Buck Converter

Transcription

1 40V, 3A, 500KHz DC/DC Buck Converter Product Description The is an efficiency and low-cost buck converter with integrated low RDS(ON) high-side 100mΩ MOSFET switch. It is capable of delivering 3A continuous output current over a wide range of supplying voltage from 8V to 40V. With a simple voltage divider, the output voltage is easily adjustable from 1.22V to 24V. Other features such as 500kHz PWM frequency, programmable soft-start, total fault-free protection and low 35μA shutdown current/ 1.2mA quiescent current make ideally to be used in application like automotive equipments and networking devices. The is available in popular PSOP-8 green package with exposed pad. Features 8V to 40V Input Voltage Range Adjustable Output from 1.22V to 24V Continuous 3A Output Current Integrated 100mΩ MOSFET Switch 1.22V Voltage Reference with ±2% Accuracy Low 35μA Shutdown Current Low 1.2mA Quiescent Current Fixed 500kHz Switching Frequency Rapid Response Current Mode Operation Over Voltage and Current Limit Over Temperature Protection Available in PSOP-8 package RoHS Compliant, 100%Pb & Halogen Free Applications FPGA,DSP,ASIC Power Supplies Green Electronics/Appliances Networking Systems Distributed Power Systems Notebook Computers Set-Top Box Automotive Electronics Wireless Communication Device LCD Monitor/ LCD TV Functional Block Diagram 1

2 Packages & Pin Assignments PSF (PSOP-8) Name NO. Description BS 1 High-side MOSFET switch gate drive boost input. Connect at least 100nF capacitor from LX to BS to control the High-Side switch. Place the capacitor close to this pin. V IN 2 Power Input. Drive IN with an 8V to 40V power source to activate the converter. LX 3 Switching Output. LX is the switching node that generate PWM waveforms to the output. GND 4 Power ground. FB 5 COMP 6 EN 7 SS 8 Feedback Input. FB pin monitors the voltage offset from output to regulate output voltage. Use a voltage divider feedback from the output to drive FB pin. 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. Chip Enable. Pull EN high to enable the regulator, pull it low to turn it off. Pull up with a 100kΩ resistor to start it up automatically. Soft-Start Control. SS controls the soft-start time. A 10nF capacitor sets the soft-start time to 0.5ms typically. Leave SS unconnected to disable this feature. Typical Application 2

3 Ordering Information GS Brand Name Part Number GS 5485B PS F Package Code Pb Free Code Part Number Package Quantity PSF PSOP PCS Marking Information Absolute Maximum Ratings (Note 1) Symbol Parameter Value Units V IN Supply Voltage Range -0.3 to 42 V V LX Switch Voltage Range -1 to V IN +1 V V BS Boost Voltage Range (V LX -0.3) to (V LX +6) V - All Other Pins Voltage Range -0.3 to +6 V T J Operating Junction Temperature Range -40 to +160 C T STG Storage Temperature Range -65 to +150 C T LEAD Lead Temperature (Soldering 10 sec) 260 C HBM ESD Rating(Human Body Model) ±2 KV MM ESD Rating(Machine Model) ±200 V Note 1: Stress beyond those listed at absolute maximum rating table may cause permanent damage to the device. These are stress rating ONLY. For functional operation are strongly recommend follow up recommended operation conditions table. Recommend Operating Ratings Symbol Parameter Value Units V IN Supply Voltage Range 8 to 40 V V OUT Output Voltage Range 1.22 to 24 V T A Operating Free-air Temperature Range -40 to +85 C θ JA Thermal Resistance Junction to Ambient 50 C/W θ JC Thermal Resistance Junction to Case 10 C/W 3

4 Electrical Characteristics V IN =24V, T A =25ºC, unless otherwise specified. Symbol Parameter Test Conditions Min Typ Max Units V IN Input Voltage V I Q Supply Current V EN =2.0V, Non-Switching ma I SHDN Shutdown Supply Current V EN =0V ua V FB Feedback Voltage 8V V IN 40V V R DS(ON)H High-Side MOSFET R DS(ON) mω R DS(ON)L Low-Side MOSFET R DS(ON) Ω I LIM Current Limit A A EA Error Amplifier Voltage Gain V/V G EA G CS Error Amplifier Transconductance COMP to Current Sense Transconductance μʊ Ʊ F OSC Oscillation Frequency KHz F OSC-SH Short Circuit Oscillation Frequency V FB =0V KHz D MAX Maximum Duty Cycle V FB =1.0V % T ON(MIN) Minimum On Time ns V EN(TH) EN Shutdown Threshold Voltage V EN Rising V EN Input Low Current V EN =0V ua Soft-Start Bias Current ua T SD Thermal Shutdown Threshold Thermal Shutdown Hysteresis

5 Function Description The is a fixed frequency, current mode synchronous buck converter. During normal operation, the internal MOSFET switch is controlled by the gate driver and dominates the duty cycle of the PWM waveform. While the switch is turned off, the inductor current flows through the external diode. PWM Oscillation The frequency of the internal oscillator is fixed at 500KHz. In case of short circuit (output/feedback voltage is zero), frequency will be down to 100KHz to reduce the heat and minimize the power consumption. Error Amplifier The error amplifier compares the voltage of FB pin with the internal voltage reference V REF. When the output current increases, the voltage of FB pin decreases and the error amplifier output will start to increase. This will force the gate driver to increase the duty cycle of the PWM waveform and raise the inductor current to compensate the output voltage drop. Chip Enable The has an EN pin to perform chip enable control. The regulator can be enabled and disabled by simply applying state logic values on EN pin. The precision values of the rising threshold is 1.0V and the falling threshold is 0.8V. Never leave the EN pin floating and make sure the value of the logic away from the voltage region of rising threshold and falling threshold. Short Circuit Protection Once the output is shorted to ground, the protection circuit will be activated and the oscillation frequency will be reduced to lower frequency around 100KHz to prevent the inductor current increasing beyond the current limit. The PWM frequency will be back to its typical value 500KHz after the short condition is removed. Input Capacitor Selection The requires an input decoupling capacitor and a bulk capacitor is needed depending on the application. A ceramic capacitor about 10uF is recommended for the decoupling capacitor. An additional 0.1uF speed-up capacitor near pin 2 to ground is good to provide additional high noise filtering. The capacitor voltage rating needs to be greater than the maximum input voltage. Output Capacitor Selection The output capacitor is required to stabilize the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. If non-low ESR electrolytic capacitors are used, limit the total value of the C OUT lower than 470μF. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by : Thermal Protection Thermal shutdown is implemented to prevent the chip from operating at exceedingly high temperatures. When the silicon die temperature is higher than its upper threshold, it forces the whole chip entering shutdown state. When the temperature is lower than its lower threshold, it resumes the normal operation. Output Voltage The internal reference V REF is 1.22V(Typical).The output voltage is divided by a resistor, R1 and R2 to the FB pin. The output voltage is given by : Input Supply Voltage V IN supplies current to internal control circuits and output voltages. The supply voltage range is from 8V to 40V. A power on reset(por) continuously monitors the input supply voltage. The buck converter draws pulsed current with sharp edges each time the upper switch turns on, resulting in voltage ripples and spikes at supply input. A minimum 10uF ceramic capacitor with shortest PCB trace is highly recommended for bypassing the supply input. The characteristics of the output capacitor also affect the stability of the regulation system. The can be optimized for a wide range of capacitance and ESR values. PCB Layout Recommendation 1. Keep the input switching current loop as small as possible. 2. Keep the LX pin as physically small and short as possible to minimize parasitic capacitance and inductance and to minimize radiated emissions. 3. Keep analog and non-switching components away from switching components. 4. Do not allow switching current to flow under the device. 5. Output capacitor should be connected to a broad pattern of the GND. 6. Voltage feedback loop should be as short as possible, and preferably with ground shield. 7. Extra via is preferable for IN, LX and GND connection. 8. C IN /C OUT should be placed as near as possible to the device. 5

6 Typical Characteristics 6

7 Typical Characteristics (continue) 7

8 Package Dimension PSOP-8 PLASTIC PACKAGE Dimensions SYMBOL Millimeters Inches MIN NOM MAX MIN NOM MAX A A A A b b c c D E E E e 1.27BSC h L L BSC θ

9 NOTICE Information furnished is believed to be accurate and reliable. However Globaltech Semiconductor assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties, which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Globaltech Semiconductor. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information without express written approval of Globaltech Semiconductor. CONTACT US GS Headquarter 4F.,No.43-1,Lane11,Sec.6,Minquan E.Rd Neihu District Taipei City 114, Taiwan (R.O.C) Wu-Xi Branch No.21 Changjiang Rd., WND, Wuxi, Jiangsu, China (INFO. &. TECH. Science Park Building A 210 Room) sales_cn@gs-power.com Version_1.0 NOTICE