1、 Application Notes: AN_SY8088 High Efficiency 1.5MHz, 1A Synchronous Step Down Regulator AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 1 General Description SY8088 is a high efficiency 1.5MHz synchronous step down DC/DC regulator IC capable of delivering up to 1A outp
2、ut current. It can operate over a wide input voltage range from 2.5V to 5.5V and integrate main switch and synchronous switch with very low RDS (ON) to minimize the conduction loss. Ordering Information Package Code Temperature CodeOptional Spec Code( )SY8088Temperature Range: -40C to 85C Features L
3、ow RDS(ON) for internal switches (top/bottom) 260m /170m 2.55.5V input voltage range 40 A typical quiescent current High light load efficiency High switching frequency 1.5MHz minimizes the external components Internal soft-start limits the inrush current 100% dropout operation RoHS Compliant and Hal
4、ogen Free Compact package: SOT23-5 Applications ortable Navigation Device Set Top Box USB Dongle Media Player Smart phone Typical Application Figure1. Schematic Diagram Figure2. Efficiency Ordering Number Package Type Note SY8088AAC SOT23-5 1A AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential-
5、 Prepared for Customer Use Only 2 Pinout (Top View) (SOT23-5) Top Mark: LD (device code: LD, Pin Name Pin Number Pin Description EN 1 Enable control. Pull high to turn on. Do not float. GND 2 Ground pin. LX 3 Inductor pin. Connect this pin to the switching node of the inductor. IN 4 Input pin. Decou
6、ple this pin to the GND pin with at least 4.7uF ceramic capacitor. FB 5 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).Add optional C1 (10pF47pF) to speed up the transient response. Abs
7、olute Maximum Ratings (Note 1) Supply Input Voltage - 6.0V Enable, FB Voltage- VIN + 0.6V Power Dissipation, PD TA = 25C, SOT23-5- 0.6W Package Thermal Resistance (Note 2) JA - 170C/W JC - -130C/W Junction Temperature Range -125C Lead Temperature (Soldering, 10 sec.) - 260C Storage Temperature Range
8、 - -65C to 150C Recommended Operating Conditions (Note 3) Supply Input Voltage - 2.5V to 5.5V Junction Temperature Range - -40C to 125C Ambient Temperature Range - -40C to 85C AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 3 Electrical Characteristics (VIN =
9、5V, VOUT = 2.5V, L = 2.2uH, COUT = 10uF, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage Range VIN 2.5 5.5 V Quiescent Current IQ IOUT=0, VFB=VREF 105% 40 A Shutdown Current SHDN EN=0 0.1 1 A Feedback Reference Voltage VREF 0.588 0.6 0.612 V PFET
10、 RON RDS(ON),P 260 m NFET RON DS(ON),N 170 m PFET Current Limit ILIM 1.3 A EN rising threshold VENH 1.5 V EN falling threshold ENL 0.4 V Input UVLO threshold VUVLO 2.5 V UVLO hysteresis HYS 0.1 V Oscillator Frequency FOSC 1.5 MHz Min ON Time 80 ns Max Duty Cycle 100 % Soft Start Time TSS 1 ms Therma
11、l Shutdown Temperature TSD 160 C Thermal Shutdown Hysteresis THYS 15 C Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the oper
12、ational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2: JA is measured in the natural convection at TA = 25C on a low effective single layer thermal conductivity test board
13、 of JEDEC 51-3 thermal measurement standard. Exposed Paddle of DFN package is the case position for JC measurement. Note 3: The device is not guaranteed to function outside its operating conditions. AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 4 Typical Per
14、formance Characteristics AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 5 AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 6 Operation The SY8088 is a high-efficiency 1.5MHz synchronous step-down DC-DC converters capable
15、 of delivering up to 1A output current. It operates over a wide input voltage range from 2.5V to 5.5V and integrates main switch and synchronous switch with very low RDS(ON) to minimize the conduction loss. Applications Information Because of the high integration in the SY8088 IC, the application ci
16、rcuit based on this regulator IC is rather simple. Only input capacitor CIN, 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 outp
17、ut 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 100k and 1M is highly recommended for both resistors. If R2=120k is chosen, then R1 can be calculated to be: 2OUT1(V0.6V)RR0.6VInput capacitor CIN
18、: A typical X7R or better grade ceramic capacitor with 6V rating and greater than 4.7uF capacitance is recommended. To minimize the potential noise problem, place this ceramic capacitor really close to the IN and GND pins. Care should be taken to minimize the loop area formed by CIN, and IN/GND pins
19、. 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 X7R or better grade ceramic
20、 capacitor with 6V rating and greater than 4.7uF 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
21、 inductance is calculated as: OUTOUTIN,MAXSWOUT,MAX40%V(1V/V)LFIwhere Fsw is the switching frequency and Iout,max is the maximum load current. The SY8088 regulator IC is quite tolerant of different ripple current amplitude. Consequently, the final choice of inductance can be slightly off the calcula
22、tion 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. OUTOUTINMAXSATMINOUTMAXSWV(1-V/V,)I,I,2FL3) The DCR of the inductor and the core loss at the switchin
23、g frequency must be low enough to achieve the desired efficiency requirement. It is desirable to choose an inductor with DCR50mohm to achieve a good overall efficiency. Short Circuit Protection: SY8088 integrates hic-cup mode hard short protection function. If output voltage is below 40% of the regu
24、lation voltage, the internal soft-start node and the error amplifier output will be reset immediately. IC works in hic-cup protection mode. The hiccup frequency is about 250Hz, and the hic-cup duty is 50%. If the hard short condition is removed, IC will go back to normal operation. Load Transient Co
25、nsiderations: The SY8088 regulator IC integrates the compensation components to achieve good stability and fast transient responses. In some applications, adding a 22pF ceramic cap in parallel with R1 may further speed up the load transient responses and is thus recommended for applications with lar
26、ge load transient step requirements. Layout Design: The layout design of SY8088 regulator is relatively simple. For the best efficiency and minimum noise problems, we should place the following components close to the IC: CIN, L, R1 and R2. 1) It is desirable to maximize the PCB copper area connecti
27、ng to GND pin to achieve the best thermal and noise performance. If the board space allowed, a ground plane is highly desirable. 2) CIN must be close to Pins IN and GND. The loop area formed by CIN and GND must be minimized. 3) The PCB copper area associated with LX pin must be minimized to avoid th
28、e potential noise problem. AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 7 4) The components R1 and R2, and the trace connecting to the FB pin must NOT be adjacent to the LX net on the PCB layout to avoid the noise problem. 5) If the system chip interfacing
29、with the EN pin has a high impedance state at shutdown mode and the IN pin is connected directly to a power source such as a LiIon battery, it is desirable to add a pull down 1Mohm resistor between the EN and GND pins to prevent the noise from falsely turning on the regulator at shutdown mode. AN_SY
30、8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 8 SOT23-5 Package outline & PCB layout design 0.550.95 TYP 0.30 -0.502.80 -3.10Recommended Pad Layout 0.3 -0.6 1.0 -1.31.90 TYP0.95 TYPNotes: All dimensions are in millimeters. All dimensions dont include mold flash &
31、 metal burr. AN_SY8088 AN_SY8088 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 9 Taping & Reel Specification 1. SOT23-5 taping orientation Feeding direction 2. Carrier Tape & Reel specification for packages Package types Tape width (mm) Pocket pitch(mm) Reel size (Inch) Reel width(mm) Trailer length(mm) Leader length (mm) Qty per reel SOT23-5 8 4 7“ 8.4 280 160 3000 3. Others: NA 3.9/4.1 1.45/1.55
