SC8902A 2S lithium battery charging and discharging

SC8902A is a synchronous buck-boost forward charging and reverse discharging converter. It integrates 4 low Rdson power tubes and has ultra-high conversion efficiency to reduce heat loss. At the same time, it can reduce the BOM of peripheral devices to the maximum extent and optimize PCB space. and cost. Regardless of whether VBUS is above, below or equal to the battery voltage, SC8902A can effectively manage the charging of 1 to 3 batteries. When the system needs to obtain energy from the battery, SC8902A supports reverse discharge of the battery. SC8902A adopts current control mode, supports ultra-wide input and output voltages from 2.7V to 22V, and can easily achieve bidirectional operation through the control of the DIR pin. SC8902A supports input current limit, output current limit, dynamic power management, dynamic output voltage adjustment, internal current limit, output short circuit and over-temperature protection, ensuring that the chip can work safely under various abnormal conditions. The SC8902A single chip implements charging and discharging functions, has ultra-high conversion efficiency, and supports DPDM charging handshake, simplifying the customer's peripheral circuit design. SC8902A is available in QFN-40 6x6 package.

============The above text is copied from Nanxin official website================

● I made a small thing myself. The requirement is that it can be plugged in and run, and when unplugged, it can provide 9V30W+ power through the lithium battery.

● I searched around for power bank solutions. I wanted to use 5358 at first, but the maximum output was 22.5W, which failed to meet my requirements. I found this chip later.

● I am not an electronics major, so I used Baidu Translator to read the English version of DATASHEET (why can’t I get a Chinese version of domestic chips????).

● It basically meets my needs. If the current is not limited, it should be no problem to charge and discharge up to 36W.

● Can be charged by DC or TYPEC.

● I don’t know why I can’t charge my phone through the PD cable. In discharge mode, when I connect the phone, the discharge light is also on, but the phone doesn’t show charging.

● The chip's built-in over-discharge protection is 2.6V, which is too low, so I added a 3V over-discharge protection and charge balance.

● When using GreenLink's fast charger, it will sometimes be recognized as 9V*2.5A, and sometimes it will be recognized as 4.5V*5A, both of which can charge up to 22.5W. (Xiaomi’s 33W really rubbish can only run 9V*2A)

● The discharge no-load value is 9.18V (I don’t know why it is different from what DATASHEET calculated).

● The measured current limiting resistor is 6.8K+6.8K (2A+4A). According to DATASHEET, it should be 60K. I don’t know why.

● It has a heavy load start-up function, and it is in non-current limiting mode at the moment of power on (I used a multimeter to directly short-circuit and measured 11A).

● The efficiency should be okay, and so should the heat generation. I don’t know how to measure pressure drop, ripple, etc., and I don’t have the equipment.

● I am a newbie with zero basic knowledge. If I look through it, some of the capacitances of the seam monsters created by copying may be unreasonable. It seems that there is too much cloth, which is ridiculous.