BQ25171-Q1: Battery Detection

Hi Furkan,

Could you clarify a bit more on the battery detection? Do you want to detect the presence of a battery when adapter is connected?

Since this is a non- powerpath device- the host is directly powered off the battery.  

Regards,

Gautham

Hello,

We need to detect whether a battery is connected to the system. Battery may be removed anytime during the operation of the system. We must change the status of an LED if a battery is connected/ disconnected.

i.e:

      LED is green if a battery is connected
      LED turns red if battery is disconnected etc.

Hello

I will take over this post.  Gautham thanks from supporting.

The BQ25171 does not have a battery detect feature and will not get an LED indication of the battery not present.  Typical behavior is output capacitor will charge up to 4.2V then stop charge when voltage drops the charge will restart.  The STAT 2 led will cycle in this mode.

It may be possible to use the voltage on TS pin to detect a no NTC condition.  This would require NTC to be part of the battery pack and removed with it and external circuit.  

Thank you Bill for the reply.

In emergency lighting we use LiFEPO4, NiMH and NiCD. BQ25171 covers the most types so it seems to be a very good solution for our products. What we are trying to achieve is to leave the battery related work (charging/ fault detection etc.) to the IC and monitor it with an MCU.

We will solve the battery detection in some other way not related to the BQ25171. However, we need a short-circuit protection for the output of BQ25171.

As far as I can tell, there exist a protection on chip but could not understand the logic behind it. Typical application shows predefined resistor values connected to the VSET-ISET-CHM_TMR inputs and then the tables show some resistor values that indicate short-circuit condition. Why would the resistor values change once the output is shorted?

"Once a valid resistor value has been detected, the corresponding charge voltage is latched in and the pin is not continuously monitored during operation. A change in this pin will not be acknowledged by the IC until the input supply or CE pin are toggled."

So do I need to toggle CE pin periodically in order to detect if a short is present at output? What will happen to the charge cycles then?

1. How actually does the IC respond to output short condition?

2. For our project, Vin = 18V ___  Vout=  2-cell LiFePO4 @ 7.00V  ___ Iout = 100mA will end up 11V*100mA = 1.1W of power dissipation on the chip. Device enters thermal regulation @125C.

With the statement, RθJA  -> 60.3 °C/W, With and ambient temperature of 30C, a total of 96C, I think we should be OK with a good PCB design to support heat sink under the IC, right? 

---

So what basically we need is:

- Output current shall be limited once a short circuit condition occurs at the output. It shall revert back to normal once short condition is fixed. However, if the IC itself cannot provide this functionality, we have an MCU running in parallel as well, so any pin signal requirement (toggle CE etc.) can be achieved through the use of MCU.

- Digital output pins from the Battery Charge IC in order to monitor the operation of the IC, charging/ full charge, fault conditions (short + open etc.). -> STAT pins

- Temperature monitoring is not necessary. -> OK

- Adjustable output current -> OK

Hello

1. How actually does the IC respond to output short condition?--Bill J - The device has output short circuit protection that will limit output current to 16ma until the voltage is high enough to enter Pre-charge or charge. 

Update--The 16mA applies to Li-Ion and LiFePO.  The NiMH configuration output current is ISET value, no pre-charge or short current reduction at lower voltage.

2. For our project, Vin = 18V ___  Vout=  2-cell LiFePO4 @ 7.00V  ___ Iout = 100mA will end up 11V*100mA = 1.1W of power dissipation on the chip. Device enters thermal regulation @125C.-- Bill J -- Yes the device will enter thermal regulation and reduce charge current to hold junction temp at 125C.  The battery will charge but a less than 100mA. 

Update---The input OVP trip point is 18V, this will turn off the output.  Recommend a lower Vin.

Hello,

Thank you for the reply.