芯美电子 EUP3412 1.5A/1.5MHz, Synchronous Step-Down Converter with Soft Start DESCRIPTION FEATURES The EUP3412 is a synchronous current mode step-down dc-dc converter, capable of driving 1.5A load current with excellent line and load regulation. Operating with an input voltage range between 2.5V and 5.5V, the device is ideal for portable applications powered by a single Li-Ion battery cell or by 3-cell NiMH/NiCd batteries. The EUP3412 operates at a fixed switching frequency of 1.5MHz and PWM operation provides very low output ripple voltage for noise sensitive applications. The internal integrated synchronous switch increases efficiency while eliminates the need for an external Schottky diode. The EUP3412 is available in the 10-pin MSOP and 10-pin TDFN package. z z z z z z z z z z z z z z High Efficiency up to 96% 1.5A Available Load Current 300µA Typical Quiescent Current 1.5MHz Constant Switching Frequency 2.5V to 5.5V Input Voltage Range Adjustable Output Voltage as Low as 0.7V 100% Duty Cycle Low Dropout Operation No Schottky Diode Required Short Circuit and Thermal Protection Excellent Line and Load Transient Response ＜1µA Shutdown Current Soft Start Function Available in MSOP-10 and TDFN-10 Package RoHS Compliant and 100% Lead(Pb)-Free APPLICATIONS z z z z z Cellular and Smart Phones Portable Media Players/ MP3 Players Digital Still and Video Cameras Portable Instruments WLAN PC Cards Typical Application Circuit Figure 1. DS3412 Ver1.0 Apr. 2008 1 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Pin Configurations Package Type Pin Configurations Package Type MSOP-10 Pin Configurations TDFN-10 Pin Description Name MSOP-10 TDFN-10 DESCRIPTION EN 1 1 VIN 2,3,6 2,3,6 GND 4 4 Analog ground. FB 5 5 SW 7,8 7,8 PGND 9,10 9,10 Feedback pin. Switch node connection to inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. Power ground. Chip enable pin. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. Do not leave EN floating. Supply voltage input. Block Diagram Figure 2. DS3412 Ver1.0 Apr. 2008 2 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Ordering Information Order Number Package Type EUP3412MIR1 MSOP-10 EUP3412JIR1 TDFN-10 Marking xxxxx P3412 xxxxx P3412 Operating Temperature Range -40 °C to 85°C -40 °C to 85°C EUP3412 □ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type M: MSOP J: TDFN DS3412 Ver1.0 Apr. 2008 3 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Absolute Maximum Ratings Input Supply Voltage ----------------------------------------------------------- -0.3V to 6V EN, FB Voltages ---------------------------------------------------------------- -0.3V to VIN P-Channel Switch Source Current (DC) -----------------------------------------1.7A N-Channel Switch Sink Current (DC) ---------------------------------------------1.7A Peak SW Sink and Source Current -------------------------------------------------2.6A Operating Temperature Range ----------------------------------------------- -40°C to 85°C Junction Temperature ------------------------------------------------------------------- 125°C Storage Temperature ------------------------------------------------------- -65°C to 150°C Lead Temp (Soldering, 10sec) ------------------------------------------------------260°C Electrical Characteristics The ● denote the Spec. apply over the full operating temperature range, otherwise Spec. are TA=25℃. VIN=3.6V unless otherwise specified. Symbol VIN UVLO Parameter EUP3412 Min Typ Max. Conditions Unit Input Voltage Range ● 2.5 5.5 V Input Undervoltage Lockout ● 1.5 2.3 V IFB Feedback Current 0 VFB Regulated Feedback Voltage TA=25°C (Note 1) -40°C≤TA≤85°C (Note 1) ● nA 0.49 0.5 0.51 0.485 0.5 0.515 V ∆VFB Reference Voltage Line Regulation VIN=2.5V to 5.5V 0.26 0.4 %/V ∆VOUT Output Voltage Line Regulation VIN=2.5V to 5.5V 0.26 0.4 %/V ILOAD=0mA to 1500mA 0.1 VLOADREG Output Voltage Load Regulation ∆VOVL Output Overvoltage Lockout ∆VOVL=VOVL-VFB IQ Quiescent Current VFB=0.45V, ILOAD=0A ISHDN Shutdown Current VEN=0V IPK Peak Inductor Current VIN=3V, VFB=0.45V fOSC Oscillator Frequency RPFET RDS(ON) of P-Channel FET ISW=200mA ● 132 210 mΩ RNFET RDS(ON) of N-Channel FET ISW=200mA ● 126 210 mΩ ILSW SW Leakage Current VEN=0V, VSW=0 or 5V, VIN=5V 1 µA VEN EN Threshold 1.5 V IEN EN Leakage Current 1 µA VFB=0.45V 20 % ● ● 50 80 mV 300 400 µA 0.1 1 µA 1.9 2.4 1.2 1.5 VFB=0V A 1.8 750 -1 ● 0.3 1.0 kHz Note 1: The EUP3412 is tested in a proprietary test mode that connects FB to the output of the error amplifier. DS3412 Ver1.0 Apr. 2008 MHz 4 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Typical Operating Characteristics DS3412 Ver1.0 Apr. 2008 5 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Typical Operating Characteristics (continued) DS3412 Ver1.0 Apr. 2008 6 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Typical Operating Characteristics (continued) DS3412 Ver1.0 Apr. 2008 7 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Application Information The EUP3412 uses a slope-compensated constant frequency, current mode architecture. Both the main (P-Channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. During normal operation, the EUP3412 regulates output voltage by switching at a constant frequency and then modulating the power transferred to the load each cycle using PWM comparator. The duty cycle is controlled by three weighted differential signals: the output of error amplifier, the main switch sense voltage and the slope-compensation ramp. It modulates output power by adjusting the inductor-peak current during the first half of each cycle. An N-channel, synchronous switch turns on during the second half of each cycle (off time). When the inductor current starts to reverse or when the PWM reaches the end of the oscillator period, the synchronous switch turns off. This keeps excess current from flowing backward through the inductor, from the output capacitor to GND, or through the main and synchronous switch to GND. Soft-Start The EUP3412 has an internal soft-start circuit that limits the inrush current and output voltage overshoot during startup. The soft-start is implemented with a digital circuit increasing the switch current in steps. ∆IL = V VOUT1 − OUT VIN (f)(L) 1 The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 1800mA rated inductor should be enough for most applications (1.5A+300mA). The DC-resistance of the inductor directely influences the efficiency of the converter. Therefore for better efficiency, choose a low DC-resistance inductor. CIN and COUT Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. The primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current drawn by the EUP3412. A low ESR input capacitor sized for the maximum RMS current must be used. The size required will vary depending on the load, output voltage and input voltage source impedance characteristics. A typical value is around 22µF. The input capacitor RMS current varies with the input voltage and the output voltage. The equation for the maximum RMS current in the input capacitor is: Short-Circuit Protection As soon as the output voltage drops below 50% of the nominal output voltage, the converter switching frequency as well as the current limit is reduced to 50% of the nominal value. Output Overvoltage Protection The output voltage is monitored by a comparator through FB pin. It guards against transient overshoots >10% by turning the main switch off and keeping it off until the fault is removed. Input Undervoltage Lockout The undervoltage lockout circuit prevents device misoperation at low input voltages. It prevents the converter from turning on the switch or rectifier MOSFET with undefined conditions. Inductor Selection The EUP3412 typically uses a 2.2uH output inductor. Larger or smaller inductor values can be used to optimize the performance of the device for specific operation conditions. The output inductor is selected to limit the ripple current to some predetermined value, typically 20%~40% of the full load current at the maximum input voltage. Large value inductors lower ripple currents. Higher VIN or VOUT also increases the ripple current as shown in equation. A reasonable starting point for setting ripple current is ∆IL=600mA (40% of 1.5A). DS3412 Ver1.0 Apr. 2008 I RMS =I O × V V O × 1 − O V V IN IN The output capacitor COUT has a strong effect on loop stability. The selection of COUT is driven by the required effective series resistance (ESR). ESR is a direct function of the volume of the capacitor; that is, physically larger capacitors have lower ESR. Once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple ∆VOUT is determined by: 1 ∆VOUT ≅ ∆IL ESR + 8fC OUT When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. 8 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Output Voltage Programming The output voltage is set by a resistive divider according to the following formula: R2 VOUT = 0.5V 1 + R1 The external resistive divider is connected to the output, allowing remote voltage sensing as shown below. PC Board Layout Checklist For all switching power supplies, the layout is an important step in the design especially at high peak currents and switching frequencies. If the layout is not carefully done, the regulator might show stability problems as well as EMI problems. When laying out the printed circuit board, the following guidelines should be used to ensure proper operation of the EUP3412. 1. The input capacitor CIN should connect to VIN as closely as possible. This capacitor provides the AC current to the internal power MOSFETs. 2. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 3. The FB pin should connect directly to the feedback resistors. The resistive divider R1/R2 must be connected between the COUT and ground. 4. Keep the switching node, SW, away from the sensitive FB node. Thermal Considerations To avoid the EUP3412 from exceeding the maximum junction temperature, the user will need to do a thermal analysis. The goal of the thermal analysis is to determine whether the operating conditions exceed the maximum junction temperature of the part. The temperature rise is given by: TR=(PD)(θJA) Where PD=ILOAD2 × RDS(ON) is the power dissipated by the regulator ; θJA is the thermal resistance from the junction of the die to the ambient temperature. The junction temperature, TJ, is given by: TJ=TA+TR Where TA is the ambient temperature. TJ should be below the maximum junction temperature of 125°C. DS3412 Ver1.0 Apr. 2008 9 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 Packaging Information MSOP-10 SYMBOLS A A1 D E1 E L b e D1 E2 DS3412 Ver1.0 Apr. 2008 MILLIMETERS MIN. MAX. 1.10 0.00 0.15 3.00 3.00 4.70 5.10 0.40 0.80 0.17 0.33 0.50 1.80 1.66 INCHES MIN. 0.000 MAX. 0.043 0.006 0.118 0.118 0.185 0.016 0.006 0.201 0.031 0.013 0.020 0.071 0.065 10 联系电话：１５９９９６４４５７９ ８３１５１７１５ 芯美电子 EUP3412 TDFN-10 SYMBOLS A A1 D1 D E1 E L b e D1 DS3412 Ver1.0 Apr. 2008 MILLIMETERS MIN. MAX. 0.70 0.80 0.00 0.05 2.50 2.90 3.10 1.70 2.90 3.10 0.30 0.50 0.18 0.30 0.50 2.40 INCHES MIN. 0.028 0.000 MAX. 0.031 0.002 0.098 0.114 0.122 0.067 0.114 0.012 0.007 0.122 0.020 0.012 0.020 0.094 11 联系电话：１５９９９６４４５７９ ８３１５１７１５