BQ 24253 no battery current limit

Hello Wesley,

When a battery is attached is the current limit up to 500mA?

My first thought for what might be happening is that when you attached the charger to the USB port it runs through the BC1.2 detection and identifies the port as 100mA.

Can you give me the EN1 & EN2 configuration you are using and if you have been able to draw 500mA from this port in other configurations?

Hi Ryan,

Thanks for the quick reply. EN1 is pulled HI and EN2 is pulled low. ILIM resister is 250 ohms to set the input current at 1 amp. I have been able to pull 500 ma from a power supply that does not have its D+ and D- lines connected, so as far as the BQ sees, they are floating and therefore non compliant I believe. 

From further reading I believe the enumeration identifies the port as SDP, but since there is no battery it adheres to the dead battery provision stated in the USB spec. This limits the input current to 100mA until the battery is sufficiently charged. I realize this is the spec, however I cannot power my load until the 500mA is available.

Is there a way around this?The only solution I can think of is to use a comparator or jumpers to short he D+ and D- pins when the battery isnt there, therefore tricking the chip into thinking it is a non compliant charger and setting the input current limit to 500mA. When a battery is present (even if it is very dead) it will leave the D+ and D- pins connected. 

Wesley

Hello Wesley,

I would think that the Power Path would serve as a work around to something like the Dead Battery Provision.

I will think about what might be happening but in the mean time I want to rule out a few other possible causes.

How do you have the load connected to the charger? To the SYS or the BAT pin?

Could you provide a schematic of how you have the charger connected?

Hi Ryan,

There is no load connected to the charger, it is a requirement of my circuit that it must be able to operate without a battery present. Please see the schematic attached. 

Wesley

4265.DipTrace Schematic - Maglite PS.pdf 

Hello Wesley,

Have you been able to measure that incoming current to the charger? Does it correspond with the 100mA limit for the charger or is at a different level?

What are the characteristics of the secondary regulator that you have on the SYS rail, Part Number and expected input range and output voltage and current? What is the desired output voltage?

Hi Ryan,

Yes the incoming current corresponds to the 100mA limit. The secondary regulator is a TPS62160, which will handle anywhere from 3V-17V i believe. It is set up to regulate to 2.4 volts. The secondary reg needs to source 0.4A, and from some performance testing I have found the overall circuit to be approximately %83 efficient at 2.4V and 0.4A. 

From looking at the output with a scope it is quite obvious that the BQ isnt supplying enough current to the secondary reg, and it is locking out. 

Wesley

Hi Ryan,

Are you still looking into this? Even with a battery connected, the BQ will not charge it when connected to a laptop, pointing to an enumeration issue. When I attach it to a power supply with the D+ and D- lines floating, it charges. 

Wesley

Hi Wesley,

Once the D+/D- detection is completed, you can change the EN1/EN2 settings to overwrite the limit that is set by D+/D-. For example, you can set EN1=0, EN2=0 before powering up the device, then after D+/D- completes, change EN1 to 1, so that the ILIM will be determined by the external resistor. Note that the the initial status on EN pins do not matter, instead, the change on EN pins will trigger the ILIM change. Please let me know if this works for you.

Thanks,

Wenjia