Using the energy storage characteristics of capacitors and inductors, through the high-frequency switching action of controllable switches (MOSFETs, etc.), the input electric energy is stored in the capacitor (inductor), and when the switch is turned off, the electric energy is released to the load again to provide energy. This is a switching power supply. Its output power or voltage capability is related to the duty cycle (the ratio of the switch conduction time to the entire switch cycle). Switching power supplies can be used for boosting and bucking.

DC-DC converters use MOSFET switches to store energy in inductors and generate current when they are closed. When the switch is opened, the stored energy of the inductor is output to the load through a diode.

Working efficiency

①Inductive DC-DC converter: The conversion efficiency of an inductive DC-DC converter powered by a battery is 80%~85%, and its loss mainly comes from external diodes and modulator switches.

②Charge pump without voltage regulation: It is a basic charge pump (such as TC7660H). It has a very high power conversion efficiency (generally over 90%), because the loss of the charge pump mainly comes from the ESR of the capacitor and the on-resistance (RDS-ON) of the internal switch tube, and both can be made very low.

③Charge pump with voltage regulation: It adds a low-dropout linear regulator after the output of the basic charge pump. Although it provides voltage regulation, its efficiency is reduced due to the power consumption of the back-end regulator. To achieve the highest efficiency, the output voltage of the charge pump should be as close as possible to the voltage regulated by the back-end regulator.

The best choice is: charge pump without voltage regulation (in applications that do not require strict output regulation), or charge pump with voltage regulation (if the pressure difference between the two ends of the back-end regulator is small enough).

Installation size

①Inductive DC-DC converter: Although many new inductive DC-DC converters can provide SOT packages, they usually still require physically large external inductors. Moreover, the circuit layout of the inductive DC-DC converter itself also requires a larger board-level space (additional decoupling, special grounding treatment, shielding, etc.).

②Charge pump without voltage regulation: The charge pump does not use an inductor, but requires an external capacitor. The new charge pump devices use SOP packages and operate at higher frequencies, so they can use small capacitors (1μF) that occupy less space. The space occupied by the charge pump IC chip and the external capacitor together is smaller than the inductor in the inductive DC-DC converter. It is also easy to obtain positive and negative combined output voltages using a charge pump. For example, the TCM680 device can support an output voltage of +2 UIN with only external capacitors. To obtain the same output voltage with an inductive DC-DC converter, two independent converters are required, or a transformer with a complex topology structure is required if one converter is used.

③Charge pump with voltage regulation: Adding a discrete back-end voltage regulator occupies more space, but many such regulators have SOT-shaped packages, which relatively reduce the occupied space. New charge pumps with voltage regulation, such as TCM850, integrate the charge pump, back-end voltage regulator and shutdown control in a single 8-pin 50lC package.

The best choice is: charge pump without voltage regulation or with voltage regulation.

Quiescent current

①Inductive DC-DC converter: Frequency modulation (PFM) inductive DC-DC converter is the switch-mode DC-DC converter with the smallest quiescent current. By using frequency modulation for voltage regulation, it can minimize the supply current at small load currents.

②Charge pump without voltage regulation: The quiescent current of the charge pump is proportional to the operating frequency. Most new charge pumps operate at frequencies above 150kHz, so they can use 1μF or even smaller capacitors. To overcome the problem of large quiescent current caused by this, some charge pumps have shutdown input pins to turn off the charge pump when it is idle for a long time, thereby reducing the supply current to near zero.

③Charge pump with voltage regulation: The back-end voltage regulator increases the quiescent current, so the charge pump with voltage regulation is worse than the basic charge pump in terms of quiescent current.

The best choice is: inductive DC-DC converter, especially frequency modulation (PFM) switch.

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Minimum operating voltage

①Inductive DC-DC converter: Battery-powered dedicated inductive DC-DC converters (such as TC16) can start working at voltages as low as 1V or even lower, so they are very suitable for electronic devices powered by a single battery cell.

②Charge pump without voltage regulation/charge pump with voltage regulation: The minimum operating voltage of most charge pumps is 1.5V or higher, so they are suitable for applications with at least two batteries.

The best choice is: inductive DC-DC converter.

Noise generated

①Inductive DC-DC converter: The inductive DC-DC converter is the source of power noise and switch radiation noise (EMI). Wideband PFM inductive DC-DC converters generate noise over a wide frequency band. The working frequency of the inductive DC-DC converter can be increased to make the noise it generates fall outside the system's frequency band.

②Charge pump without voltage regulation/charge pump with voltage regulation: The charge pump does not use an inductor, so its EMI effect can be ignored. Pump input noise can be eliminated by a small capacitor.

The best choice is: charge pump without voltage regulation or with voltage regulation.

Integration

①Inductive DC-DC converter: Chips that integrate switch regulators and other functions (such as voltage detectors and line regulators) have been developed. For example, the TC16 chip integrates a PFM boost converter, LD0 and voltage detector in an SO-8 package. Compared with discrete implementation schemes, such devices provide excellent electrical performance and occupy less space.

②Charge pump without voltage regulation: Basic charge pumps, such as TC7660, have no integrated additional functions and occupy less space.

③Charge pump with voltage regulation: The integration of more functions of charge pumps with voltage regulation has become a current development trend. Obviously, the next generation of charge pumps with regulation will have a degree of functional integration comparable to that of inductive DC-DC converter integrated chips.

The best choice is: inductive DC-DC converter.

Output regulation

①Inductive DC-DC converter: The inductive DC-DC converter has good output regulation capability. Some inductive DC-DC converters also have external compensation pins that allow "fine-tuning" the output transient response characteristics according to the application.

②Charge pump without voltage regulation: Such devices have no output voltage regulation, they simply convert the input voltage into negative or double output voltage. Therefore, the output voltage will decrease as the load current increases. Although this is not a problem for some applications (such as LCD bias), it is not suitable for applications that require a stable output voltage.

③Charge pump with voltage regulation: It provides voltage regulation (stabilization) through a back-end linear voltage regulator (on-chip or external). In some cases, it is necessary to add switch stages to the charge pump to provide enough headroom for the back-end regulator, which requires additional external capacitors, which will have a negative impact on size, cost and efficiency. But the back-end linear regulator can make the output voltage stability of the charge pump with regulation as good as that of the inductive DC-DC converter.

The best choice is: charge pump with voltage regulation.

Installation cost

①Inductive DC-DC converter: In recent years, the cost of using inductive DC-DC converters has gradually decreased, and the demand for external components has also become less. But the inductive DC-DC converter requires at least one external inductor, capacitor and Schottky diode. The diode, inductor, plus the relatively high-priced switch converter chip, make its total cost higher than that of the charge pump.

②Charge pump without voltage regulation: The charge pump without voltage regulation is cheaper than the inductive DC-DC converter and only requires external capacitors (no inductors), saving board space, inductor cost, and shielding cost in some cases.

③Charge pump with voltage regulation: The cost of the charge pump with voltage regulation is roughly equivalent to that of the inductive switch-mode DC-DC converter itself. In some cases, an external back-end voltage regulator can be used to reduce costs, but it will increase the required installation space and reduce efficiency.

The best choice is: The best choice for situations where strict stabilization is not required is a charge pump without voltage regulation; for situations where output voltage stabilization is required, the cost of choosing a charge pump with voltage regulation and an inductive DC-DC converter is roughly equivalent.

Applying the above best choice tips to design applications will be more conducive to saving time and cost and improving efficiency.