Application Guide for Common Power Management Chips in Portable Products

Commonly used power management chips for portable products

●Low Dropout Regulators (LDO Linear Regulators)

LDO

VLDO;

●DC/DC Converters based on inductor energy storage (Inductor Based Switching Regulators)

Buck

Boost

Buck-Boost;

● Charge Pumps (Switched Capacitor Regulators) based on capacitor energy storage;

●Battery Chargers;

● Lithium Battery Protection;

Considerations for selecting power management chips

● Select products from manufacturers with mature production technology and excellent quality;

● Choose chips with high operating frequency to reduce the application cost of peripheral circuits;

● Choose chips with small packages to meet the volume requirements of portable products;

● Choose manufacturers with good technical support to facilitate solving problems in application design;

● Choose chips with complete product information, easy sample and DEMO application, and large-scale supply;

● Choose chips with good performance/price ratio;

LDO Linear Low Dropout Regulator

The LDO linear low dropout regulator is the simplest linear regulator and can only step down the input voltage to a lower voltage due to its inherent DC switchless voltage conversion. Its biggest disadvantage is in terms of heat management, because its conversion efficiency is approximately equal to the value of the output voltage divided by the input voltage. For example, if an LDO driving an image processor has a nominal 3.6V input power supply from a single lithium battery and outputs 1.8V at a current of 200mA, the conversion efficiency is only 50%, thus creating some hot spots in the phone and shortening the battery life. Although these disadvantages do exist in terms of larger input and output voltage differences, the situation is different when the voltage difference is smaller. For example, if the voltage drops from 1.5V to 1.2V, the efficiency becomes 80%.

When a 1.5V main supply is used and needs to be stepped down to 1.2V to power the DSP core, a switching regulator has no clear advantage. In fact, a switching regulator cannot be used to step down 1.5V to 1.2V because the MOSFET cannot be fully boosted (either on-chip or off-chip). Standard low-dropout (LDO) regulators are also not up to the task because their dropout voltage is usually higher than 300mV. The ideal solution is to use a very low dropout (VLDO) regulator with an input voltage range close to 1V, a dropout voltage of less than 300mV, and an internal reference close to 0.5V. Such a VLDO regulator can easily step down the voltage from 1.5V to 1.2V with a conversion efficiency of 80%. Since the power level at this voltage is usually around 100mA, a power loss of 30mW is acceptable. The output ripple of the VLDO can be less than 1mVP-P. Low ripple can be easily ensured by using the VLDO as a post regulator of a step-down switching regulator.

Switching DC/DC Buck-Boost Regulator

● When the voltage difference between input and output is high, the switching regulator avoids the efficiency problems of all linear regulators. It achieves efficiencies up to 96% by using low resistance switches and magnetic storage cells, thus greatly reducing power losses in the conversion process.

● Selecting a DC/DC with a high switching frequency can greatly reduce the size and capacity of external inductors and capacitors, such as a high switching frequency of more than 2MHz.

● The disadvantages of switching regulators are relatively minor and can usually be overcome with good design techniques. However, the frequency leakage interference of inductors is difficult to avoid, and their EMI radiation needs to be considered when designing applications.

● According to their functions, switching DC/DC buck-boost regulators are divided into Buck switching DC/DC buck regulators, Boost switching DC/DC boost regulators and Buck-Boost switching DC/DC buck-boost regulators that can automatically switch between buck and boost functions when the voltage of the lithium battery drops from 4.2V to 2.5V.

Charge Pump

Capacitor charge pumps achieve voltage boost through switch arrays and oscillators, logic circuits, and comparison controllers, using capacitors to store energy. Charge pumps do not require inductors, but require external capacitors. They operate at higher frequencies, so small ceramic capacitors (1μF) can be used to minimize space occupancy and reduce cost. Charge pumps can provide ±2 times the output voltage using only external capacitors.

Its loss mainly comes from the ESR (equivalent series resistance) of the capacitor and the RDS (ON) of the internal switching transistor. The charge pump converter does not use an inductor, so its radiated EMI can be ignored. The input noise can be filtered out with a small capacitor. Its output voltage is precisely preset during factory production, and the adjustment capability is achieved through the back-end on-chip linear regulator. Therefore, when designing the charge pump, the number of switch stages of the charge pump can be increased as needed to provide enough room for the back-end regulator. The charge pump is very suitable for the design of portable application products. From the internal structure of the capacitive charge pump, it is actually a system on a chip.

Comparison of Linear Regulators and Switching Regulators

The comparison between linear regulators and switching regulators can be clearly seen from the table below.