1 DC-DC Fundamentals 1.4 Charge Pump Regulator XIANG FANG: Hello. Welcome to the DC-DC Fundamentalists. I'm Xiang. In this section, we will talk about the charge pump regulator.
2 What is a Charge Pump Regulator? The charge pump regulator is a kind of switching regulator that delivers power by only alternatively charging and discharging capacitors.It’s suitable applications with low load current and moderate input to output voltage differenceQ1Q3Q2Q4CFLOAD+VINCoVo-IoVCFWhat is a charge pump regulator? It is a kind of switching regulator that delivers the power by only charging and discharging capacitors. It's suitable for application that has low currents and has moderate input to output voltage difference.
3 Pros and Cons Advantages Disadvantages No inductor is needed, smaller sizeModerate Efficiency, higher than linear regulatorsVout can be higher or lower than VinFewer components needed make the charge pump easier to design and lower costSwitching produces higher output ripple & noiseThe output current capacity is limited by the capacitorsThe advantage of using charge pump regulator is that it has no inductor in the regulator. You can achieve smaller size. The efficiency is moderate, but it's higher than the linear regulator. And the Vout can be higher or lower than your Vin. And fewer components are needed, so it makes it easy to decide and use. The disadvantage is that the switching can produce high output ripples and noise. And the output current capacity is limited by the capacitor.
4 How Does a Charge Pump Work? The capacitors connection is altered by the switches so that the charge and discharge is controlledSwitches S1, S3 and S2, S4 are switching in complementary:S1, S3 on, S2, S4 off, chargingS1, S3 off, S2, S4 on, dischargingBy reversing the connections of the output to ground, the unity gain converter becomes negative gain inverterUnity gainInverting gainHow does a charge pump work? The capacitor connection is altered by the switches so that the charge and discharge are controlled. As you can see on this simplified graph here, the switch S1 to S4 are switching. When S1 and S3 are on, S2 and S4 are off. The capacitor is charging by the input voltage source. And when the switch one, S1, S3 is off, then the ends S2 and S4 will switch on. And the charge capacitor-- you can discharge to the output load. And it's also interesting to know by reversing the connection of the output and ground, you can get from a unity gain converter to a negative gain inverter.
5 Voltage DoublerThe voltage doubler circuit shown below still has a single capacitor in the topology, only the connections are differentThe switching of the four switches are still the sameS1, S3 on, S2, S4 off, gain phaseS1, S3 off, S2, S4 on, common phaseHowever, in the common phase, the input source is still connected to the capacitor: Vout = Vc + Vin = 2VinVoltage DoublerOn this page, we show a popular configuration of the charge pump regulator. It's called a voltage doubler. As you can see, it's very similar to the unity gain charge pump regulator. And actually, it requires four switches. And these four switches are switching similar. It's switching the same as the unity gain regulator. But instead of connecting your Vout ground to the ground, your Vout is actually on top of your Vin. So in this case, your Vout is actually your Vin plus the capacitor's voltage. So that will give you two times Vin output. So that's why it's called the voltage doubler.By swapping Vin and Vout, the same doubler circuit will give half gain
6 More Gain Combinations Include two capacitors in the charge pump, and many different gain can be generated by varying the connection combinationsThe following figure shows some configuration of two capacitor connection and the resulting gain that can be achieved:And for the previous two slides, we only show using one capacitor in this regulator. So if you have two capacitors in the charge pump regulator, that actually gives you more combination of the gain configurations. And the following figures show some typical configuration of two capacitor's connections. And a different gain can be achieved.Same common phase connection for all gains*Assuming C1 = C2
7 Charge Pump Regulation By including a post regulator stage, the charge pump can achieve fine granular of the output voltageAlso, the switch impedance can be controlled to act effectively as a post regulatorRout is the effective output impedance including the switch impedance Rsw, and the switched cap impedance (1/Fsw*Cf)Fine adjustment can be accomplished by controlling Fsw or RswCharge pump regulations. By including a post regulator stage, the charge pump can achieve fine granular of the output voltage. Also the switch impedance can be controlled to act effectively as a post regulator. As you can see, instead of using switch S1 and S3, it's actually replaced by a linear regulator type of transistor. And the Rout is the effective output impedance, including the switch impedance off switch and the switch cap impedance, which is determined by the frequency of your switch and the capacity of the CFCAP. And fine adjustment can be accomplished by controlling the switching frequency and the switch impedance.
8 Charge Pump Regulation Control the frequency: Pulse- Frequency Modulation (PFM)The output voltage is held constant by skipping unneeded pulsesAdvantages: very low quiescent current, higher efficiencyDisadvantages: Higher output voltage ripple, frequency variesControl the resistance: Constant- Frequency RegulationRegulate the output by changing the resistance of the internal switchesAdvantages: low voltage ripple, fixed frequencyDisadvantage: high quiescent currentAnd there are two types of charge pump regulations. One, is by controlling the frequency. We call it pulse-frequency modulation. As you can see here, the output voltage is how constant by skipping the unneeded pulse. And an advantage of using the PFM is that it has very low quiescent currents. And you can achieve high efficiency, especially at lie-low condition. But the disadvantage is that it has high output voltage ripple. And your frequency varies. And the other type-- we call it constant frequency regulation. It's achieved by controlling the resistance of the switch. In this type of regulation, the advantage is that you can achieve low voltage ripple. And the switching frequency is relatively fixed. But the disadvantage is it has a high quiescent current. So the efficiency is lower.8
9 Summary Introduction to charge pump regulator The operation and configuration of switching regulatorThe charge pump regulationIn summary, in this section, we introduced the charge pump regulator, and operation, and regulation, of this type of DC-DC converter.