WT2595M50

WEITRON 2A Step-down Voltage Regulator P b Lead(Pb)-Free Power Converter 150kHz General Description: WT2595M The WT2595M is a monolithic integrated circuit that provide all the active functions for a step-down switching regulator, capable of driving a 2A load without additional transistor component. Requiring a minimum number of external component, the board space can be saved easily. The external shutdown function can be controlled by TTL logic level and then come into standby mode. The internal compensation makes feedback control have good line and load regulation without external design. Regarding protected function, thermal shutdown is to prevent over temperature operating from damage, and current limit is against over current operating of the output switch. The WT2595M operates at a switching frequency of 150Khz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Other features include a guaranteed +4% tolerance on output voltage under specified input voltage and output load conditions, and +15% on the oscillator frequency. The output version included fixed 3.3V, 5V, 12V, and an adjustable type. The packages are available in a standard 8-lead SOP8. Features: * 3.3V, 5V, 12V and adjustable output versions * Adjustable version output voltage range, 1.23V to 37V +4% max over line and load condiction * SOP-8 packages * Voltage mode non-synchronous PWM control * Thermal-shutdown and current-limit protection * ON/OFF shutdown control input * Input voltage range up to 40V * Output load current: 2A * 150 kHz fixed frequency internal oscillator * Low power standby mode * Built-in switching transistor on chip Applications: * Simple High-efficiency step-down(buck) regulator * Efficient preregulator for linear regulators * On-card switching regulators * Positive to negative converter * Battery Charger WEITRON hpp://www.weitron.com.tw 1/9 28-Sep-06 WT2595M Ordering Information Part Number WT2595M33 WT2595M50 WT2595M12 WT2595M Voltage 3.3V 5.0V 12.0V ADJ Package SOP-8 SOP-8 SOP-8 SOP-8 Packing Type 2,500Units / Tape & Reel 2,500Units / Tape & Reel 2,500Units / Tape & Reel 2,500Units / Tape & Reel Connection Diagrams Surface Mount Package (Top View) SOP- 8 GND GND GND GND Pin Descriptions Name VIN Out Gnd FB Description Operating voltage input Switching output Ground Output voltage feedback control ON/OFF Shutdown 8765 WT YWW 2595M 50 1234 Vin Vout Y WW ON/OFF FB =Year =Weekly ON/OFF http://www.weitron.com.tw WEITRON 2/9 28-Sep-06 WT2595M Ty pical Application Circuit FB DC Input Vin 1 12V WT2595M -33 4 8 SD 76 5 3 2 Out L1 33uH 3.3V/2A Output Load Inductor Capacitor Cin Gnd Schottky Diode D1 Capacitor Co Function Description Pin Functions +VIN This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. Out Internal switch and power output. The voltage at this pin switches between (+VIN – VSAT) and approximately – 0.5V, with a duty cycle of approximately VOUT / VIN. The PC board copper area connected to this pin should be kept a minimum in order to reduce the coupling sensitivity to the circuitry Ground Circuit ground. Feedback Complete the feedback loop by sensing the regulated output voltage ON /OFF Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 100uA. Pulling this pin below a threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin above 1.3V (up to a maximum of 25V) shuts the regulator down. If this shutdown feature is not needed, the ON /OFF pin must be wired to the ground pin, in either case the regulator will be in the ON condition. Thermal Considerations The SOP-8 package needs a heat sink under most condictions . The size of the heatsink depends on the input voltage, the output voltage, the load current and the ambient temperature. The WT2595M junction temperature rises above ambient temperature for a 2A load and different input and output voltages. The data for these curves was taken with the WT2595M operating as a buck switching regulator in an ambient temperature of 25oC (still air). These temperature increments are all approximate and are affected by many factors. Some of these factors include board size, shape ,thickness ,position ,location, and even board temperature. Other factors are trace width, total printed circuit copper area, copper thickness , single or double-sided, multi-layer board and amount of solder on the board. Higher ambient temperatures require more heat sinking. For the best thermal performance ,wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (One exception is the out(switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat(lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further. The effectiveness of the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board , as well as whether the surrounding air is still or moving. Furthermore, some of these components such as the catch diode will add heat to the PC board and heat can vary as the input voltage changes. For the inductor, depending on the phical size, type of core material and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board. http://www.weitron.com.tw WEITRON 3/9 28-Sep-06 WT2595M Block Diagram SD VIN 200mV Current Source bias 1.235V Reference 2.5V Regulator Start up 220mV + Com_ p Comp + + FB _ Comp + Absolute Maximum Ratings Symbol VCC VSD VFB VOUT PD TST TOP VOP Parameter Rating +45 -0.3 to +25 -0.3 to +25 -1 Internally limited -65 to +150 -40 to +125 +4.5 to +25 Unit V V V V W o o Supply Voltage ON/OFF Pin input voltage Feedback Pin voltage Output voltage to Ground Power dissipation Storage temperature Operating temperature Operating voltage http://www.weitron.com.tw WEITRON _ Amp Pre-driver 150kHz OSC. Thermal Limit 4/9 _ 2A Switch Output Gnd C C V 28-Sep-06 WT2595M Electrical Characteristics Unless otherwise specified, VIN=12V for 3.3V, 5V, adjustable version and V IN=24V for the 12V version. ILOAD = 0.2A Symbol IB FOSC Fscp VSAT DC ICL IL IQ ISTBY VIL VIH IH IL Ts Parameter Feedback bias current oscillator frequency Oscillator frequency short circuit protect saturation voltage Max. Duty Cycle(ON) Min. Duty cycle(OFF) current limit Output = 0 Output = 1 Output leakage current Conditions VFB=1.3V (Adjustable version only) Min. Typ. -10 Max. -50 -100 173 173 70 1.4 1.5 Unit nA Khz Khz V % 127 of When current limit occurred and VFB