SS882X Boost supports the maximum load capacity of 1A, and in emergency charging scenarios, SS882X Boost supports limiting current by hardware in order to support devices with large charge current such as mobile phones. In actual application scenarios, if SS882X Boost current limit does not match the undervoltage protection function of a mobile phone or other device, compatibility issues such as the inability to charge the mobile phone may occur. The specific instructions are as follows.
1. The principle of Boost current limit and undervoltage protection for charging
Take the SS882X charge a mobile phone via Boost as an example：
If the charge current of the mobile phone is greater than the output current limit of Boost, then Boost will reduce the output voltage to achieve the purpose of reducing the charge current of the mobile phone. At the other end, the charger management unit of the mobile phone detects that the charge voltage (output voltage of Boost) is below a certain threshold (undervoltage), and will reduce the charge current to avoid further pulling down the charge voltage, which is called undervoltage protection. Finally, the discharge device (SS882X) and the charge device (mobile phone) cooperate with each other to finally achieve the purpose of current limiting and stable charge.
2. Features of SS882X Boost output current limit
The limited current of SS882X Boost output can be configured by register and supported up to 1A. At the same time, the BSTOK threshold of SS882X has two settable levels, 4.3V and 4.5V, in the actual application scenario, if the desired output current limit value has not been obtained, Boost will keep reducing the output voltage until it is below the BSTOK threshold, the Boost output will be turned off, resulting in the inability to charge the phone, which is the compatibility problem we encounter.
3. Features of undervoltage protection for mobile phones and other devices
Whether compatibility problems are encountered is determined by the undervoltage protection characteristics of the mobile phone, the current limit value of Boost, and the BSTOK threshold of Boost.
If there is a compatibility problem in the application, we can test the undervoltage protection feature of the target phone as follows:
Connect the mobile phone charge cable with a power or battery, and charge the mobile phone through the charge cable. Limiting the output current of the power or battery to 2A (basically safe for the current mobile phones), adjusting the voltage from 5V to small in turn, observing and recording the change of charge current (Note: each voltage adjustment must wait for a while to stabilize before determining how much the corresponding charge current is at this voltage).
Below is a diagram of the test wiring of a mobile phone and the change of the current captured with the voltage.
4. Summary
In actual charging, if the charge voltage of the mobile phone drops to around the threshold of BSTOK (4.3V or 4.5V), and the charge current is still greater than the output current limit of Boost, the Boost output voltage will continue to drop, causing Boost to turn off, and compatibility problems will occur.
To solve the problem, there are two methods that can be used：
1）Set the threshold of BSTOK to the lowest (4.3V)
2）Increase the current limit of the boost output as much as possible.
Original article, Please mark the attribution when reprinting. SINHMICRO，www.sinhmicro.com。