Analysis of PMIC chips and applications

PMIC is the abbreviation of power management IC. It is characterized by high integration and packaging of traditional multi-output power supplies in one chip, which makes multi-power application scenarios more efficient and smaller.

In the CPU system, we often use the PMIC. Such as set-top box design, intelligent voice speaker design, large industrial equipment design.

PMIC in the set top box

The following is a introduction to the PMIC through the chip AXP152. This is a highly integrated PMIC from the core, which is mainly used in digital cameras, set-top boxes, network equipment, monitoring equipment and other products.

Introduction to XP152

The AXP152 is a highly integrated power management IC that integrates an adaptive and usb compatible PWM charger, four buck converters (Buck DC-DC converters), and seven LDOs. It also has protection circuits such as overvoltage/undervoltage protection (OVP/UVP), overtemperature protection, and overcurrent protection (OCP) to ensure the safety and stability of the power system.

The AXP152 package is available in a 5x5 40-pin QFN package. As shown below.

In addition, the AXP152 includes a two-wire serial interface (TWSI) that allows the CPU to enable/disable certain power outputs and program voltages to reduce power loss, providing more complete power management.

AXP152 internal block diagram

Through the above block diagram, we can see that there is a large logic control unit inside the PMIC. All DC-DC and most LDOs are controlled by the logic module. It only needs to configure the TWSI interface and change the corresponding configuration register to control the DC. -DC and LDO output, register configuration manual we can refer to the datasheet.

In addition, the SCK/SDA pin of the TWSI interface of the AXP152 has been pulled up inside the chip, so the host device (CPU) can be flexibly monitored and configured through this interface.

4-way DC-DC and 7-way LDO

The figure below is a comparison of the 4-way DC-DC.

4-way DC-DC

It can be seen that the output voltage of the four DC-DCs is adjustable, and the adjustable range is from 0.7 to 3.5V, which can meet the power supply requirements of most minimum systems. For example, the CPU power supply is 3.3V, and the EMMC is 3.3V or 1.8V. Electricity, DDR for 1.25 to 1.35V. These sets of DC-DCs are all achievable.

DC-DC1 and 3 have a voltage regulation accuracy of 50mV/step, and DC-DC2 and 4 have a voltage regulation accuracy of 25mV/step. If the system requires high voltage accuracy adjustment, DC-DC with an accuracy of 25mV/step can be used. .

The figure below is a comparison of the 7-way LDO.

7 groups of LDOs

These 7 groups of LDOs are generally supplied to the peripherals of the system, such as SRAM or PLL power supply, WiFi Bluetooth module power supply, control circuit power supply, drive circuit power supply, sensor power supply, peripheral interface power supply, etc., the output voltage is between 0.7V-5V, When using, pay attention to the output current. If the LDO of the PMIC is not satisfied, the external DC-DC or LDO should be supplied with power.

In these groups of LDOs, both ALDO1/2 and GPIOLDO are low-noise LDOs, and analog circuit power supplies should be connected to these low-noise LDOs.

Overload and current limit protection

All DC-DC and LDOs support self-monitoring and current limiting. When the load current exceeds the drive capability, all output voltages will be reduced to protect the internal circuitry. When the DC-DC output voltage is lower than the set voltage of 85%, the PMIC will automatically turn off.

typical application

Application block diagram

In the application, we connect the TWSI interface of AXP152 through the I2C interface of the CPU. In addition, we need to give the enable signal and reset signal. It can be seen that for each DC-DC, it only needs to be regarded as a discrete DC-DC to configure. Just fine.

The output capacitor is recommended to use a low ESR ceramic capacitor of 10uF X7R. When the output voltage is higher than 2.5V, a 3.3uH power inductor is recommended. In addition, the saturation current of the selected inductor should be more than 50% larger than the maximum required current of the circuit.