SY8089AAC

Application Note: AN_SY8089/SY8089A High Efficiency 5.5V, 2A continuous, 3A peak, 1MHz Synchronous Step Down Regulator General Description Features The SY8089 and SY8089A are high-efficiency, high frequency synchronous step-down DC-DC regulator IC capable of delivering up to 2A output current. The SY8089 and SY8089A operate over a wide input voltage range from 2.7V to 5.5V and integrate main switch and synchronous switch with very low RDS(ON) to minimize the conduction loss. Low output voltage ripple and small external inductor and capacitor sizes are achieved with greater than 1MHz switching frequency. SY8089 integrates short circuit and over-voltage latch off protection. Ordering Information SY8089 ( ) Temperature Code Package Code Optional Spec Code Temperature Range: -40°C to 85°C Ordering Number Package type SY8089AAC SOT23-5 SY8089AAAC SOT23-5 Low RDS(ON) for internal switches (top/bottom):110m /80m 2.7-5.5V input voltage range 2A continuous, 3A peak load current capability 1MHz switching frequency minimizes the external components Internal softstart limits the inrush current Reliable short circuit protection: SY8089: Latch off protection SY8089A: Hic-cup mode protection Reliable over-voltage protection: SY8089: Latch off protection SY8089A: No latch off protection 100% dropout operation RoHS Compliant and Halogen Free Compact package: SOT23-5 Applications Note LCD TV Set Top Box Net PC Mini-Notebook PC Access Point Router Typical Applications Figure 1.Schematic diagram AN_SY8089/A Rev. 0.9 Figure 2. Efficiency vs Load Current Silergy Corp. Confidential- Prepared for Customer Use Only 1 SY8089/8089A Pinout (top view) SOT23-5 Part Number SY8089AAC SY8089AAAC Pin Name EN GND LX IN FB Pin Number 1 2 3 4 5 Package type SOT23-5 SOT23-5 Top Mark JX KV Pin Description Enable control. Pull high to turn on. Do not float. Ground pin. Inductor pin. Connect this pin to the switching node of inductor. Input pin. Decouple this pin to GND pin with at least 10µF ceramic cap. Output Feedback Pin. Connect this pin to the center point of the output resistor divider (as shown in Figure 1) to program the output voltage: Vout=0.6*(1+R1/R2). Absolute Maximum Ratings (Note 1) Supply Input Voltage ----------------------------------------------------------------------------------------------- -0.3V to 6.0V Enable, FB Voltage------------------------------------------------------------------------------------------ -0.3V to VIN + 0.6V Power Dissipation, PD @ TA = 25°C, SOT23-5 -------------------------------------------------------------------------------------------------------------- 0.6W Package Thermal Resistance (Note 2) JA --------------------------------------------------------------------------------------------------------------- 170°C/W JC ----------------------------------------------------------------------------------------------------------------130°C/W Junction Temperature Range ----------------------------------------- ------------------------------------------ -40°C to 150°C Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------------------- 260°C Storage Temperature Range ------------------------------------------------------------------------------------- -65°C to 150°C Recommended Operating Conditions (Note 3) Supply Input Voltage ------------------------------------------------------------------------------------------------ 2.7V to 5.5V Junction Temperature Range ------------------------------------------------------------------------------------ -40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------- -40°C to 85°C AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 2 SY8089/8089A Block Diagram (SY8089) AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 3 SY8089/8089A (SY8089A) AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 4 SY8089/8089A Electrical Characteristics (V IN = 5V, VOUT = 2.5V, L = 2.2µH, COUT = 22µF, TA = 25°C, unless otherwise specified) Parameter Input Voltage Range Quiescent Current Symbol VIN IQ Shutdown Current Feedback Reference Voltage FB Input Current PFET RON ISHDN VREF IFB RDS(ON), P RDS(ON), N ILIM VENH VENL VUVLO VHYS FOSC VSCP NFET RON PFET Current Limit EN rising threshold EN falling threshold Input UVLO threshold UVLO hysteresis Oscillator Frequency Short Circuit Protection Latch Off Threshold Min ON Time Max Duty Cycle Soft Start Time Output Discharge Switch On Resistance Thermal Shutdown Temperature Test Conditions Min 2.7 IOUT=0, VFB=VREF 105% EN=0 VFB=VIN Typ Max 5.5 Unit V µA 1 0.612 50 110 µA V nA m 80 m 0.2 1 0.25 A V V V V MHz V 55 0.588 -50 0.1 0.6 3.5 1.5 0.4 2.5 IOUT=500mA 75 100 TSS RDISCH 1.2 50 TSD 160 ns % ms °C Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Note 2: Test condition: Device mounted on 2” x 2” FR-4 substrate PCB, 2oz copper, with minimum recommended pad on top layer and thermal vias to bottom layer ground plane. Note 3: The device is not guaranteed to function outside its operating conditions. AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 5 SY8089/8089A Typical Performance Characteristics AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 6 SY8089/8089A AN_SY8089/A Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 7 SY8089/8089A VOUT Operation Principle SY8089 is a synchronous buck regulator IC that integrates the PWM control, top and bottom switches on the same die to minimize the switching transition loss and conduction loss. With ultra low RDS(ON) power switches and proprietary PWM control, this regulator IC can achieve the highest efficiency and the highest switch frequency simultaneously to minimize the external inductor and capacitor size, and thus achieving the minimum solution footprint. Short Circuit Protection SY8089 After the soft start is over, if the output voltage falls below 40% of the regulation level, IC will turn off both power switches, entering short circuit protection. It will remain in this state until the IN or EN voltage is recycled. (SY8089A) The frequency is folded back to about 30% of the nominal frequency and the current limit is folded back to 3.0A to prevent the inductor current from runaway and to reduce the power dissipation of the IC under short circuit conditions. Over-voltage Protection If the output voltage exceeds 120% of the regulation level for more than 20 s, IC will turn off both power switches and turn on the discharge switch, entering over-voltage protection. It will remain in this state until IN or EN voltage is recycled. Applications Information Because of the high integration in the SY8089 IC, the application circuit based on this regulator IC is rather simple. Only input capacitor C IN, output capacitor COUT, output inductor L and feedback resistors (R1 and R2) need to be selected for the targeted applications specifications. Feedback resistor dividers R1 and R2: Choose R1 and R2 to program the proper output voltage. To minimize the power consumption under light loads, it is desirable to choose large resistance values for both R1 and R2. A value of between 10k and 1M is highly recommended for both resistors. If Vout is 1.8V, R1=100k is chosen, then R2 can be calculated to be 50k.: 0.6V R2 = R1 ( ) . VOUT -0.6V AN_SY8089/A Rev. 0.9 R1 FB GND R2 Input capacitor CIN: This ripple current through input capacitor is calculated as: ICIN_RMS =IOUT D(1-D) This formula has a maximum at VIN=2VOUT condition, where ICIN_RMS=I OUT/2. This simple worst-case condition is commonly used for DC/DC design. With the maximum load current at 2.0A. A typical X5R or better grade ceramic capacitor with 6.3V rating and more than 1 pcs 22µF capacitor can handle this ripple current well. To minimize the potential noise problem, ceramic capacitor should really be placed close to the IN and GND pins. Care should be taken to minimize the loop area formed by CIN, and IN/GND pins Output capacitor COUT: The output capacitor is selected to handle the output ripple noise requirements. Both steady state ripple and transient requirements must be taken into consideration when selecting this capacitor. For the best performance, it is recommended to use X5R or better grade ceramic capacitor with 6.3V rating and greater than 22 F capacitance. Output inductor L: There are several considerations in choosing this inductor. 1) Choose the inductance to provide the desired ripple current. It is suggested to choose the ripple current to be about 40% of the maximum output current. The inductance is calculated as: L VOUT (1 VOUT /VIN, MAX ) FSW IOUT, MAX 40% where Fsw is the switching frequency and IOUT,MAX is the maximum load current. The SY8089 regulator IC is quite tolerant of different ripple current amplitude. Consequently, the final choice Silergy Corp. Confidential- Prepared for Customer Use Only 8 SY8089/8089A of inductance can be slightly off the calculation value without significantly impacting the performance. 2) The saturation current rating of the inductor must be selected to be greater than the peak inductor current under full load conditions. ISAT, MIN IOUT, MAX VOUT(1-VOUT/VIN,MAX) 2 FSW L 3) The DCR of the inductor and the core loss at the switching frequency must be low enough to achieve the desired efficiency requirement. It is desirable to choose an inductor with DCR