LTC1760 SafetySignal timing characteristics

Preventative. I'm asking this question before committing to the first schematics and board designs for charger/manager and battery. I plan to have around 4x3000mAh in each battery and sustained discharge current can reach 15A if only one of the two batteries is being discharged. The PowerPath fast algorithm should prevent the system from losing power, but possibility of mechanically interrupting this high a current worries me.

Unknown said:

it is mostly the insertion of the battery that will cause arcing and high currents

Hm. Doesn't LTC1760 only open the battery's switches after it observes the SafetySignal in a good range?

Hi Anton,

I commend your taking preventative measures here. At 15A discharge currents, it is a reasonable concern.

Unfortunately the LTC1760 doesn't do much to help you here because the turn-off is not fast. If you are powered by a battery alone (I assume that is the case here considering we are discussing the battery discharge suddenly stopping) then the charger is not monitoring the safety signal. So, it is not actually detecting battery presence. Here's a plot of what happens during battery removal:

YELLOW = GB1O, BLUE = battery node, PINK = VOUT

I have a 1A load on VOUT, otherwise it slowly droops down. You can see from this that the FET is not cutting off at all.

You can manually turn off the path if you'd like. The attached guide gives an example of how to do so.

PDF

Regards,

Zack

Hi Anton,

I commend your taking preventative measures here. At 15A discharge currents, it is a reasonable concern.

Unfortunately the LTC1760 doesn't do much to help you here because the turn-off is not fast. If you are powered by a battery alone (I assume that is the case here considering we are discussing the battery discharge suddenly stopping) then the charger is not monitoring the safety signal. So, it is not actually detecting battery presence. Here's a plot of what happens during battery removal:

YELLOW = GB1O, BLUE = battery node, PINK = VOUT

I have a 1A load on VOUT, otherwise it slowly droops down. You can see from this that the FET is not cutting off at all.

You can manually turn off the path if you'd like. The attached guide gives an example of how to do so.

PDF

Regards,

Zack

Hello Zack,

Thank you for the explanation. I was envisioning a situation where there is no DC power and both batteries are discharging, but one is near empty and the user removes it to swap in a fresh one. 15A may be a tad too conservative an estimate for discharge current from one battery, but better safe than sorry. I see that I will have to implement some sort of per-battery switch cutting off the battery either on the LTC1760 side, or on the battery side. Probably I will make virtue out of necessity and combine it with whatever mechanical latch will be locking the battery in place.

Best wishes,
Anton