CM2500

CM2500 CHAMP | Alldatasheet

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WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 1 GENERAL DESCRIPTION

FEATURES

The CM2500 is a current-mode step-down DC-DC converter that generates up to 2A output current at 380kHz switching frequency. The device utilizes advanced BCD process for operation with input voltage up to 20V consuming only 20 μA in shutdown mode, the CM2500 is highly efficient with peak efficiency at 95% when in operation. Protection features include cycle-by-cycle current limit, thermal shutdown, and frequency fold back at short circuit. The CM2500 is available in SOP-8 package and requires very few external devices for operation. ‹ 2A Output Current ‹ Up to 95% Efficiency ‹ 4.75V to 20V Input Range ‹ 20 μA Shutdown Supply Current ‹ 380kHz Switching Frequency ‹ Adjustable Output Voltag e from 1.28V to 0.85·VIN ‹ Cycle-by-Cycle Current Limit Protection ‹ Thermal Shutdown Protection ‹ Frequency Fold Back at Short Circuit ‹ Stability with Wide Range of Capacitors, ‹ SOP-8 Package

APPLICATIONS

‹ TFT LCD Monitors ‹ Portable DVDs ‹ Car-Powered or Battery-Powered Equipments ‹ Set-Top Boxes ‹ Telecom Power Supplies ‹ DSL and Cable Modems and Routers ‹ Termination Supplies TYPICAL APPLICATIONS

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 2 PIN CONFIGURATION BLOCK DIAGRAM

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 3

ORDERING INFORMATION

Part Number Temperature Range Package Packing CM2500GIS -40 ℃ ~ +85 ℃ SOP-8 TAPE & REEL ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS Output Voltage ………………….…… GND-0.3V to V IN+0.3V PIN DESCRIPTION Pin Number Pin Name Pin Description 1 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 10nF capacitor between BS and SW. 2 IN Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the Application Information section. 3 SW Switch Output. Connect this pin to the switching end of the inductor. 4 GND Ground. 5 FB Feedback Input. The voltage at this pin is regulated to 1.28V. Connect to the resistor divider between output and ground to set output voltage. 6 COMP Compensation Pin. See Stability Compensation in the Application Information section. 7 EN Enable Input. When higher than 1.85V, this pin turns the IC on. When lower than 1.7V, this pin turns the IC off. Output voltage is discharged when the IC is off. When left unconnected, EN is pulled up to 4.5V tip with a 2.5μA pullup current. 8 N/C Not Connected.

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 4 ABSOLUTE MAXIMUM RATINGS (Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.) PARAMETER VALUE UNIT IN Supply Voltage -0.3 to 20 V SW Voltage -1 to VIN + 1 V BS Voltage VSW – 0.3 to VSW + 6 V EN, FB, COMP Voltage -0.3 to 6 V Continuous SW Current Internally Limited A Junction to Ambient Thermal Resistance(θJA) 105 °C/W Maximum Power Dissipation 0.76 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C Lead Temperature (Soldering, 10 sec) 300 °C APPLICATION CIRCUIT

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 5

ELECTRICAL CHARACTERISTICS

(VIN = 12V, TA= 25°C unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT Input Voltage VIN VOUT = 5V, ILOAD = 0A to 1A 7 20 V High-Side Switch On Resistance RONH 0.22 Ω Low-Side Switch On Resistance RONL 4.7 Ω SW Leakage VEN = 0 1 10 μA Current Limit ILIM 2.6 3.3 A COMP to Current Limit Transconductance GCOMP 1.8 A/V Error Amplifier Transconductance GEA ΔICOMP = ±10μA 550 μA/V Error Amplifier DC Gain AVEA 3200 V/V Switching Frequency fSW 300 360 420 kHz Short Circuit Switching Frequency VFB = 0 50 kHz Maximum Duty Cycle DMAX VFB = 1.1V 90 % Minimum Duty Cycle VFB = 1.4V 0 % Enable Threshold Voltage Hyster esis = 0.1V 2.0 2.2 V Enable Pull Up Current Pin pulled up to 4.5V typically when left unconnected 2.5 uA Supply Current in Shutdown VEN=0 20 50 uA IC Supply Current in Operation VEN=3V , VFB=1.4V 1.0 1.5 mA Thermal Shutdown Temperature Hysteresis=10°C 168 °C

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 6 FUNCTIONAL DESCRIPTION As seen in Figure 2, Functional Block Diagram, the CM2500 is a current mode pulse width modulation (PWM) converter. The converter operates as follows : A switching cycle starts when the rising edge of the O scillator clock output causes the High- Side Power Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected to IN, the induct or current ramps up to store energy in the magnetic field. The inductor current level is measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation is higher than the COMP voltage, the out put of the PWM Comparator goes high. When this happens or when Oscillator clock output goes low, the High-Side Power Switch turns off and the Low-Side Power Switch turns on. At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again. The High- Side Power Switch is driven by logic using BS as the positive rail. This pin is charged to VSW + 6V when the Low-Side Power Switch turns on. The COMP voltage is the integration of the error between FB input and the internal 1.28V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output. Curr ent limit happens when COMP reaches its maximum clamp value of 2.55V. The Oscillator normally switches at 380kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 50kHz at VFB = 0.5V. SHUTDOWN CONTROL The CM2500 has an enable input EN for turning the IC on or off. When EN is less than 1.8V, the IC is in 8 μA low current shutdown mode and output is discharged through the Low- Side Power Switch. When EN is higher than 1.85V, the IC is in normal operation mode. EN is internally pulled up with a 2.5μA current source and can be left unconnected for always-on operation. Note that EN is a low voltage input with a maximum voltage of 6V; it should never be directly connected to IN. THERMAL SHUTDOWN The CM2500 automatically turns off when its junction temperature exceeds 170°C.

APPLICATION INFORMATION

Figure 4 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the output volt age. Typically, use RFB2 ≈ 10kΩ and determine RFB1 from the following equation: INDUCTOR SELECTION The inductor maintains a continuous current to the output load. This inductor current has a ri pple that is dependent on the inductance value: higher induct ance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an inductance value L based on the ripple current requirement: where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum output current, and KRIPPLE is t he ripple factor. Typically, choose KRIPPLE = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. With this inductor value, the peak inductor current is IOUT • (1 + KRIPPLE / 2). Make sure that this peak inductor current is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical inductor values for various output voltages are shown in Table 1. Table 1. Typical Inductor Values

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 7 INPUT CAPACITOR The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during switching, its ESR also affects efficiency. The input capacitance needs to be higher than 10 μF. The best choice is the ceramic type; howeve r, low ESR tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the output current. The input capacitor should be placed close to the IN and G pins of the IC, with the shortest traces possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1μF ceramic capacitor is placed right next to the IC. OUTPUT CAPACITOR The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, t he ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. For ceramic output capacitors, typically choose a capacitance of about 22 μF. For tantalum or electrolytic capacitors, choose a capacitor with less than 50mΩ ESR. RECTIFIER DIODE Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode must have a current rating higher than the maximum output current and a reverse voltage rating higher than the maximum input voltage. STABILITY COMPENSATION The feedback loop of the IC is stabilized by the components at the COMP pin, as shown in Fi gure 5. The DC loop gain of the system is determined by the following equation:

STEP 2. Set the zero fZ1 at 1/4 of the crossover frequency. an additional compensation capacitor CCOMP2 is required. Table 2. Typical Compensation for Different

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 9 TYPICAL PERFORMANCE CHARACTERISTICS

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 10 PACKAGE DIMENSION SOP-8

WIDE I NPUT 2A S TEP D OWN C ONVERTER 2008/04/15 Rev1.0 Champion Microelectronic Corporation Page 11 IMPORTANT NOTICE Champion Microelectronic Corporation (CMC) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involv e potential risks of death, personal injury, or severe property or environmental damage. CMC integrated circ uit products are not designed, intended, au thorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of CMC products in such applications is understood to be fully at the risk of the cust omer. In order to minimize risks associated with the customer’s applications, th e customer should provide adequate design and operating safeguards. HsinChu Headquarter Sales & Marketing 5F, No. 11, Park Avenue II, Science-Based Industrial Park, HsinChu City, Taiwan 7F-6, No.32, Sec. 1, Chenggong Rd., Nangang District, Taipei City 115, Taiwan T E L : +886-3-567 9979 T E L : +886-2-2788 0558 FAX: +886-3-567 9909 FAX: +886-2-2788 2985