MD8850

MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter ■ DESCRIPTION： MD88XX series are high efficiency, low ripple PFM step-up DC-DC Converter. The converter can start up by supply voltage as low as 0.75V, and capable of delivering maximum 300mA output current at 5V output with 3V input voltage. Quiescent current drawn from power source is as low as 4uA. All of these features make MD88XX series be suitable for portable devices, which are supplied by a single battery to four-cell batteries. MD88XX integrates output voltage feedback and compensation networks, startup circuits, oscillation circuits, PFM control circuits, stable reference circuits, overcurrent protection circuits and trimming technology, so it can afford high precision and low temperature-drift coefficient of the output voltage. MD88XX is available in SOT-89-3, SOT-23-3, SOT-89-5 and SOT-23-5 packages, which is PB free. And in 5-pin packages, such as SOT-23-5, the device can be switch on or off easily by CE pin, to minimize the standby supply current. ■ FEATURES： ■ APPLICATIONS：  Low Start-up voltage (when Iout is 1mA): 0.75V   Deliver 300mA at 5.0V Output voltage with 3.0V input Voltage  Low quiescent current: 4uA(TYP)  Low Shutdown current: 0.1uA  High power conversion efficiency: 85%(TYP)  Output voltage accuracy: ±2.5% Power Source for PDA, DSC, MP3 Player, Electronic toy and wireless mouse  Power Source for a Single or Dual-cell Battery-Powered Equipments  Power Source for LED ■ BLOCK DIAGRAM： www.md-ic.com.cn -1- MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter ■ ORDERING INFORMATION ( MD88XX ) Code Output Voltage Package Type MD8818* 1.8V MD8827* 2.7V SOT-89-3 MD8830 3.0V SOT-89-5 MD8833 3.3V SOT-23-3 MD8836 3.6V SOT-23-5 MD8850* 5.0V Marking MD88XX Note: “XX” represents output voltage. “*” indicates out of stock, and reservation must be made in advance. ■PIN CONFIGURATION： PIN DEFINATION PIN Code Symbol Description 4 Vss(GND) Ground 2 Vout SOT-89-3 SOT-89-5 SOT-23-3 SOT-23-5 1 4 1 2 2 2 Output Feedback Pin, Power supply for internal 3 5 3 5 Lx Switching Pin — 3 — 3 NC No Connection — 1 — 1 CE Chip Enable www.md-ic.com.cn -2- MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter ■ ABSOLUTE MAXIMUM RATING： Parameter Symbol Value Unit Output Voltage Range VOUT VSS-0.3～VSS+12 V CE Pin Voltage VCE VSS-0.3～VOUT+0.3 V LX Voltage VLX VSS-0.3～VSS+12 V LX Pin Output Current ILX 1000 mA 0.5 W 0.5 W 0.25 W 0.25 W SOT-89-3 Power Dissipation SOT-89-5 PD SOT-23-3 SOT-23-5 Ambient Temperature Ta -40～85 ℃ Storage Temperature Ts -40～125 ℃ Lead Temperature & Time Ts 260 ℃,10S ℃,S ■ ELECTRICAL CHARACTERISTICS： VIN=VOUT*0.6；IOUT =10mA；Ta=25℃ (Except special instruction) Value Parameter Symbol Test Condition Unit MIN TYP MAX Output Voltage Accuracy △Vout — -2.5 — +2.5 % Input Voltage Vin — — — 10 V Start-up Voltage Vstart (Fig.1) — 0.75 0.9 V Hold-on Voltage Vhold (Fig.1) — — 0.7 V Input Current Iin (Fig.1) Iout=0mA — 15 20 uA Quiescent Current IDD (Fig.2) VS = VOUT+0.5V — 4 7 uA Shutdown Current ISHDN CE=GND — — 0.5 uA Iout=1mA， Vin ：0→2V Iout=1mA， www.md-ic.com.cn Vin ：2→0V -3- MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter CE “H” threshold voltage VCEH — 0.9 — — V CE “H” threshold voltage VCEL — — — 0.6 V Switch ON Resistance RSWON — — 0.4 0.5 Ω Switch Leakage Current ILEAK(Fig.3) VS = VOUT+0.5V，VX=6V — — 0.5 uA Oscillator Frequency FOSC(Fig.3) VS = VOUT*0.95 300 350 400 kHz Oscillator Duty Cycle DOSC(Fig.3) VS = VOUT*0.95 65 75 85 % Efficiency η — — 85 — % Note: “F1g.1”, “Fig.2” and “Fig.3” in the table above indicate the label of the test circuit below. ■ TEST CIRCUITS： ■ APPLICATION CIRCUITS： SOT-89-3 and SOT-23-3 footprint www.md-ic.com.cn -4- MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter SOT-89-5 and SOT-23-5 footprint ■ SELECTION THE EXTERNAL COMPONENTS： The four main energy loss of Boost structure DC-DC converter in full load are the ESR of inductor, the voltage of Schottky diode, on resistor of internal N-channel MOSFET and its driver. Though at very low load condition, the quiescent current of chip do affect efficiency certainly. In order to improve the efficiency, MD88XX integrates low on-resistor N-channel MOSFET and well design driver circuits. The switch energy loss is limited at very low level. Thus it can be seen, the inductor and schottky diode affect the conversion efficiency greatly. The inductor and the capacitor also have great influence on the output voltage ripple of the converter. So it is necessary to choose a suitable inductor, a capacitor and a right schottky diode to obtain high efficiency, low ripple and low noise. 1、INDUCTOR SELECTION The following aspects need to be considered when selecting inductor: Firstly, we should define the minimum value of the inductor that can ensure the boost DC-DC to operate in the continuous current-mode condition. L min ≥ D(1 − D) 2 RL 2f The above expression is got under conditions of continuous current mode, neglect Schottky diode’s voltage, ESR of both inductor and capacitor. The actual value is greater that it. If inductor’s value is less than Lmin，the efficiency of DC-DC converter will drop greatly, and the DC-DC circuit will not be stable. Secondly, consider the ripple of the output voltage, DI = D • Vin Lf www.md-ic.com.cn Im ax = Vin DVin + 2 (1 − D) RL 2 Lf -5- MD88XX 上海明达微电子有限公司 PFM Step-up DC/DC Converter If inductor value is too small, the current ripple through it will be great. Then the current through diode and power switch will be great. Because the power switch on chip is not ideal switch, the energy of switch will improve. The efficiency will fall. Thirdly, in general, smaller inductor values supply more output current while larger values start up with lower input voltage and acquire high efficiency. The working frequency of MD88XX is up to 350kHz, the purpose of which is to decrease the size of external inductor. An inductor value of 3uH to 1mH works well in most applications. If DC-DC converter delivers large output current (for example: output current is great than 50mA), large inductor value is recommended in order to improve efficiency. The ESR of inductor will affect efficiency greatly. Suppose ESR value of inductor is rL，Rload is load resistor，then the energy can be calculated by following expression: Dη ≈ rL Rload (1 − D) 2 Consider all above，inductor value of 27uH, ESR