芯美电子 EUP3410 2A,25V,380KHz Step-Down Converter DESCRIPTION FEATURES The EUP3410 is a current mode, step-down switching regulator capable of driving 2A continuous load with excellent line and load regulation. The EUP3410 can operate with an input voltage range from 4.75V to 25V and the output can be externally set from 1.2V to 16V with a resistor divider. z z z z z z z z z z z Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. In shutdown mode the regulator draws 16µA of supply current. The EUP3410 requires a minimum number of readily available standard external components. 2A Output Current 0.17Ω Internal DMOS Output Switch Wide 4.75 to 25V Operating Input Range Output Adjustable from 1.2V to 16V Up to 95% Efficiency 16µA Shutdown Current Fixed 380KHz Frequency Thermal Shutdown and Overcurrent Protection Input Under Voltage Lockout Available in SOP-8 Package RoHS Compliant and 100% Lead(Pb)-Free APPLICATIONS z z z z PC Monitors Distributed Power Systems Networking Systems Portable Electronics Typical Application Circuit Figure 1. DS3410 Ver1.1 Feb. 2008 1 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Typical Application Circuit (continued) Figure 2. Block Diagram Figure 3. DS3410 Ver1.1 Feb. 2008 2 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Pin Configurations Package Type Pin Configurations SOP-8 Pin Description PIN PIN 1 BS 2 IN 3 SW 4 GND 5 FB 6 COMP 7 EN 8 N/C DS3410 Ver1.1 Feb. 2008 DESCRIPTION High-Side Gate Drive Boost Input. BS supplies the drive for the high-side n-channel 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 switch. Drive IN with a 4.75V to 25V power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor. 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. Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback threshold is 1.2V. See Setting the Output Voltage. 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. See Compensation. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator, drive EN low to turn it off. For automatic startup, leave EN unconnected. No Connect 3 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Ordering Information Order Number Package Type Marking Operating Temperature range EUP3410DIR1 SOP-8 xxxxx P3410 -40°C to 85°C EUP3410 □ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type D: SOP-8 DS3410 Ver1.1 Feb. 2008 4 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Absolute Maximum Ratings Input Voltage (VIN) ----------------------------------------------------------- -0.3V to 26V Switch Voltage (VSW) ------------------------------------------------------ -1V to VIN +0.3V Boot Strap Voltage (VBS) ------------------------------------------------ VSW-0.3V to VSW +6V All Other Pins -------------------------------------------------------------------- -0.3V to 6V Operating Temperature Range ----------------------------------------------- -40°C to 85°C Junction Temperature ------------------------------------------------------------------- 150°C Storage Temperature ------------------------------------------------------- -65°C to 150°C Lead Temp (Soldering, 10sec) ------------------------------------------------------260°C Thermal Resistance θJA (SOP-8) ----------------------------------------------------- 90°C/W Electrical Characteristics Unless otherwise specified, VEN=5V, VIN=12V ,TA=25°C. Parameter Conditions Feedback Voltage Upper Switch On Resistance Lower Switch On Resistance Upper Switch Leakage Current Limit Oscillator Frequency Short Circuit Frequency Maximum Duty Cycle Minimum Duty Cycle Enable Threshold Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis Shutdown Supply Current Operating Supply Current Thermal Shutdown DS3410 Ver1.1 Feb. 2008 4.75V ≤ VIN ≤ 25V EUP3410 Min Typ Max 1.162 1.200 0.17 6.8 VEN=0V, VSW=0V 5 2.4 320 VFB=0V VFB=1V VFB=1.5V 0.7 2 VEN=0V VFB=1.4V 1.236 3 380 45 90 0.95 2.5 110 16 0.45 160 440 0 1.4 3 30 0.7 5 联系电话：１５９９９６４４５７９ ８３１５１７１５ Unit V Ω Ω µA A KHz KHz % % V V mV µA mA °C 芯美电子 EUP3410 Typical Operating Characteristics C1=390uF, C2=0.22uF, C6=0.22uF, C7=560uF, L=15uH, TA=25℃. Efficiency versus IOUT and VOUT 95 5.0V 90 Efficiency(%) 3.3V 85 2.5V 80 VIN=10V 75 70 0 500 1000 1500 2000 Output Current(mA) DS3410 Ver1.1 Feb. 2008 6 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Typical Operating Characteristics C1=390uF, C2=0.22uF, C6=0.22uF, C7=560uF, L=15uH, 25℃. DS3410 Ver1.1 Feb. 2008 7 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Functional Description The EUP3410 is a current-mode step-down switch-mode regulator. It regulates input voltages from 4.75V to 25V down to an output voltage as low as 1.2V, and is able to supply up to 2A of load current. The EUP3410 uses current-mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and amplified through the internal error amplifier. The output current of the transconductance error amplifier is presented at COMP where a network compensates the regulation control system. The voltage at COMP is compared to the switch current measured internally to control the output voltage. Slope compensation provides stability in constant frequency architectures by preventing subharmonic oscillations at high duty cycles. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, this results in a reduction of maximum inductor peak current for high duty cycles. The converter uses an internal n-channel MOSFET switch to step down the input voltage to the regulated output voltage. Since the MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and BS drives the gate. The capacitor is internally charged while the switch is off. An internal 6.8Ω switch from SW to GND is used to insure that SW is pulled to GND when the switch is off to fully charge the BS capacitor. Application Information Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to FB (see Figure 2). The voltage divider divides the output voltage down by the ratio: VFB = VOUT ∗ R 3 / (R 2 + R 3) Thus the output voltage is : R3 Can be as high as 100KΩ, but a typical value is 10 KΩ. Using that value, R2 is determined by : R 2 ~ = 8.33 ∗ (VOUT − 1.2 )(KΩ ) For example, for a 3.3V output voltage, R3 is 10KΩ, and R2 is 17.5KΩ. Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor results in less ripple current that in turn results in lower output ripple voltage. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. Choose an inductor that does not saturate under Ver1.1 Feb. 2008 L = (VOUT ) ∗ (VIN − VOUT ) / (VIN ∗ f ∗ ∆I ) Where VOUT is the output voltage, VIN is the input voltage, f is the switching frequency, and ∆I is the peak-to-peak inductor ripple current. Input Capacitor The input current to the step-down converter is discontinuous, and therefore an input capacitor C1 is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. The input capacitor value should be greater than 10µF. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating Its RMS current rating should be greater than approximately 1/2 of the DC load current. For insuring stable operation C2 should be placed as close to the IC as possible. Alternately a smaller high quality ceramic 0.1µF capacitor may be placed closer to the IC and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. All ceramic capacitors should be placed close to the EUP3410. Output Capacitor VOUT = 1.2 ∗ (R 2 + R 3) / 3 DS3410 the worst-case load conditions. A good rule for determining the inductance is to allow the peak-to- peak ripple current in the inductor to be approximately 30% of the maximum load current. Also, make sure that the peak inductor current (the load current plus half the peak-to-peak inductor ripple current) is below the 2.4A minimum current limit. The inductance value can be calculated by the equation: The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple low. The characteristics of the output capacitor also affect the stability of the regulation control system. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: VRIPPLE ~ = 1.4 ∗ VIN ∗ (f LC / f )∧ 2 Where VRIPPLE is the output ripple voltage, VIN is the input voltage, fLC is the resonant frequency of the LC filter, f is the switching frequency. In the case of tanatalum or low ESR electrolytic capacitors, the ESR dominates the impedance at the switching frequency, and so the output ripple is calculated as: 8 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 VRIPPLE ~ = ∆I ∗ R ESR Where VRIPPLE is the output voltage ripple, ∆I is the inductor ripple current, and RESR is the equivalent series resistance of the output capacitors. Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the high-side switch is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Compensation The system stability is controlled through the COMP pin. COMP is the output of the internal transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. The DC loop gain is: A VDC = (VFB / VOUT ) ∗ A VEA ∗ G CS ∗ R LOAD approximately 1/10 of the switching frequency. In this case, the switching frequency is 380KHz, therefore use a crossover frequency, fC, of 40KHz. Lower crossover frequencies result in slower response and worse transient load recovery. Higher crossover frequencies can result in instability. Table 1. Compensation Values for Typical Output Voltage /Capacitor Combinations VOUT C7 R1 C5 C4 2.5V 3.3V 5V 12V 22µF Ceramic 22µF Ceramic 22µF Ceramic 22µF Ceramic 560µF/6.3V (30mΩ ESR) 560µF/6.3V (30mΩ ESR) 470µF/10V (30mΩ ESR) 220µF/25V (30mΩ ESR) 7.5KΩ 10KΩ 10KΩ 10KΩ 2.2nF 1.5nF 2.2nF 5.6nF None None None None 10KΩ 30nF None 10KΩ 39nF None 10KΩ 47nF None 10KΩ 56nF None 2.5V 3.3V 5V 12V Where: Choosing the Compensation Components VFB is the feedback threshold voltage, 1.2V VOUT is the desired output regulation voltage AVEA is the transconductance error amplifier voltage gain, 400 V/V. GCS is the current sense gain, (roughly the output current divided by the voltage at COMP), 2A/V RLOAD is the load resistance (VOUT / IOUT where IOUT is the output load current) The system has 2 poles of importance, one is due to the compensation capacitor (C5), and the other is due to the output capacitor (C7). These are: The values of the compensation components given in Table 1 yield a stable control loop for the output voltage and capacitor given. To optimize the compensation components for conditions not listed in Table 1, use the following procedure: Choose the compensation resistor to set the desired crossover frequency. Determine the value by the following equation: R1 = 2 π ∗ C 7 ∗ VOUT ∗ f c / (G EA ∗ G CS ∗ VFB ) Putting in the known constants and setting the crossover frequency to the desired 40KHz: f P1 = G EA / (2 π ∗ A VEA ∗ C5 ) Where P1 is the first pole, and GEA is the error amplifier transconductance (660µA/V). and R1 ≈ 1.36 × 10 8 ∗ C 7 ∗ VOUT The value of R1 is limited to 10KΩ to prevent output overshoot at startup, therefore if the value calculated for R1 is greater than 10KΩ, use 10KΩ. f P 2 = 1 / (2 π ∗ R LOAD ∗ C 7 ) The system has one zero of importance, due to the compensation capacitor (C5) and the compensation resistor (R1). The zero is: In this case, the actual crossover frequency is less than the desired 40KHz, and is calculated by: f C = R1 ∗ G EA ∗ G CS ∗ VFB / (2π ∗ C7 ∗ VOUT ) f Z1 = 1 / (2 π ∗ R1 ∗ C5 ) If a large value capacitor (C7) with relatively high equivalent-series-resistance (ESR) is used, the zero due to the capacitance and ESR of the output capacitor can be compensated by a third pole set by R1 and C4. The pole is: f P3 = 1/ (2π ∗ R1 ∗ C4 ) The system crossover frequency (the frequency where the loop gain drops to 1, or 0dB) is important. A good rule of thumb is to set the crossover frequency to DS3410 Ver1.1 Feb. 2008 Or: ( ) f C ≈ 2.94 × 10 4 ∗ R1 / (C7 ∗ VOUT ) Choose the compensation capacitor to set the zero to ¼ of the crossover frequency. Determine the value by the following equation: 9 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 ( EUP3410 ) C5 = 0.22 ∗ C 7 ∗ V / R1 OUT Determine if the second compensation capacitor, C4 is required. It is required if the ESR zero of the output capacitor happens at less than four times the crossover frequency. Or: 8π ∗ C 7 ∗ R ESR ∗ f C ≥ 1 Or: (7.39 × 10 −5 ) ∗ R1 ∗ R ESR / VOUT ≥ 1 Where RESR is the equivalent series resistance of the output capacitor. If this is the case, add the second compensation capacitor. Determine the value by the equation : C 4 = C 7 ∗ R ESR (max) / R1 Where RESR(max) is the maximum ESR of the output capacitor. DS3410 Ver1.1 Feb. 2008 10 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3410 Packaging Information SOP-8 SYMBOLS MILLIMETERS INCHES MIN. MAX. MIN. A 1.35 1.75 0.053 0.069 A1 0.10 0.25 0.004 0.010 D E 4.90 5.80 E1 MAX. 0.193 6.20 0.228 3.90 0.244 0.153 L 0.40 1.27 0.016 0.050 b 0.31 0.51 0.012 0.020 e DS3410 Ver1.1 Feb. 2008 1.27 0.050 11 联系电话：１５９９９６４４５７９ ８３１５１７１５