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SP6828EK Datasheet(PDF) 10 Page - Sipex Corporation |
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SP6828EK Datasheet(HTML) 10 Page - Sipex Corporation |
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10 / 17 page  10 SP6828DS/11 SP6828/6829 +3V Low Power Voltage Inverter © Copyright 2000 Sipex Corporation DESCRIPTION The SP6828/6829 devices are CMOS Charge Pump Voltage Converters that can be used to invert a +1.15V to +4.2V input voltage. These devices are ideal for designs involving battery- powered and/or board level voltage conversion applications. The typical operating frequency of the SP6828 is 12kHz. The typical operating frequency of the SP6829 is 35kHz. The SP6828 has a typical operating current of 20 µA and the SP6829 operates at 40 µA.Bothdevicescanoutput25mA with a voltage drop of 500mV. The devices are ideal for designs using +3.3V or +3.6V lithium ion batteries such as cell phones, PDAs, medical instruments, and other portable equipment. The SP6828/6829 devices combine a high efficiency with a low quiescent current. THEORY OF OPERATION The SP6828/6829 devices should theoretically produce an inverted input voltage. In real world applications, there are small voltage drops at the output that reduce efficiency. The circuit of an ideal voltage inverter can be found in Figure 21. The voltage inverters require two external capacitors to store the charge. A description of the two phases follows: Phase 1 In the first phase of the clock cycle, switches S2 and S4 are opened and S1 and S3 closed. This connects the flying capacitor, C1, from V IN to ground. C1 charges up to the input voltage applied at V IN. Phase 2 In the second phase of the clock cycle, switches S2 and S4 are closed and S1 and S3 are opened. This connects the flying capacitor, C1, in parallel with the output capacitor, C2. The charge stored in C1 is now transferred to C2. Simultaneously, the negative side of C2 is connected to V OUT and the positive side is connected to ground. With the voltage across C2 smaller than the voltage across C1, the charge flows from C1 to C2 until the voltage at the V OUT equals -VIN. Charge-Pump Output The output of the SP6828/6829 devices is not regulated and therefore is dependent on the output resistance and the amount of load current. As the load current increases, losses may slightly increase at the output and the voltage may become slightly more positive. The loss at the negative output, V LOSS, equals the current draw, IOUT, from V OUT times the negative converter's source resistance, R S: V LOSS = IOUT x RS. The actual inverted output voltage at V OUT will equal the inverted voltage difference of V IN and V LOSS: V OUT = -(VIN - VLOSS). Efficiency Theoretically, the total power loss of a switched capacitor voltage converter can be summed up as follows: ∑P LOSS = PINT + PCAP + PCONV, where P LOSS is the total power loss, PINT is the total internal loss in the IC including any losses in the MOSFET switches, P CAP is the resistive loss of Figure 21. Circuit for an Ideal Voltage Inverter C1 C2 S1 S3 S4 S2 VOUT VIN VOUT = -VIN |
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