There are two types of voltage regulators most often used to supply the different voltage rails on a system on a chip (SoC): linear regulators, like low dropout (LDO) regulators, and switching regulators, like the DC-DC converter.
One problem with using LDOs to generate low voltages from an incoming power supply is that they burn power relative to the amount of voltage-drop from the input to the output. If you have a relatively high voltage drop, LDOs are not efficient. In this case, it is better to use a DC-DC converter that can achieve significantly higher efficiency than an LDO. The drawback to a DC-DC converter is that it is a switched-mode circuit and can induce switching noise into its output voltage. Extremely noise-sensitive circuits should not be supplied by DC-DC converters. One possible solution to overcome this is to cascade a DC-DC converter for efficient voltage drop followed by an LDO to clean up the supply noise.
There are two types of DC-DC converter technologies:
- Standard Inductor-Based DC-DC Converters: require an external inductor and capacitor to create the DC output level
- Switched-Capacitor DC-DC Converters: can be implemented with on-die capacitors but cannot generally supply as much current as inductor-based solutions
Additionally, DC-DC converters can be used in the following modes:
- Buck Mode: where the output voltage is lower than the input voltage
- Boost Mode: where the output voltage is higher than the input voltage
- Bypass Mode: where the input voltage is supplied directly to the output
- Combination Mode: automatically supply the correct output voltage regardless of the input voltage
Buck-boost mode is particularly common in battery-powered applications. When the battery is connected to a charger or is fully charged, the battery voltage may be higher than the required voltage of the load circuitry. Then as the battery becomes discharged, the battery voltage is lower than the required voltage of the load circuitry.
Vidatronic has a switched capacitor DC-DC converter IP block called Flexsupply® that does not require any external components. It can generate the required output voltage regardless of whether the input voltage is above or below the required output voltage. This IP block is also designed to be scalable based on the required output current. For example, if your IoT SoC is only going to draw 1 milliamp from the buck-boost converter, then you use our smallest size IP module on the die. If you were to require a higher load current, then the size of the module can scale up linearly to support the additional load. For example, a 10-milliamp load would require an area 10x the size of the area as for our 1 milliamp module. This means that in your lighter-load applications you don’t pay a die-area penalty for current that you’re not using.
To learn more about DC-DC converters, check out our full white paper on selecting the proper DC-DC converter: