How do I implement emergency power shut down in LTC1760. Once in the shut down mode, how do I recover from it?
Can you kindly provide a circuit.
As you've probably referenced, here are the criteria for the emergency turn-off state:
So, you need 8V-10V on the DCDIV pin. Any way you choose to implement this is fine, but I will provide one solution here:
This assumes that your Vcc is > 8V and allows you to turn the 9V output on/off using a logic-level GPIO signal.
Let me know if you have any questions.
Thanks for all your help.
We have some additional issues:
1. We are using 10K ohm resistor between Ilimit pin and GND. With this the current should be limited to around 2.14 A max.
In our case the current seems to be going up to 4 A .
1. We have a 2 battery system. We are seeing an issue, where if each battery (1 & 2) are not evenly charged or discharged, then the charging will stop whenever the first one gets to 100%. We would definitely prefer if charging would continue until both are fully charged in this case.
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1. Make sure you are also setting the sense resistor appropriately for your current setting. Both the ILIMIT resistance and the sense resistor value need to be configured together:
2. Try fixing the current limit and see if that helps. If not, can you make sure that the second battery is still requesting to be charged? You will need to monitor the communication or poll the battery for its ChargingVoltage() and ChargingCurrent() values. Charging should continue until neither battery is requesting to be charged.
Thanks for your prompt response.
We are using 0.01 ohm sense resistor (Rsense) meaning that the AC/DC charger supply current limit is set at 10 Amps. Should this matter if we set our max battery charge current to 2 Amps (Rilimit= 10K ohms)? Per your explanation, we should be using an Rsense resistor of 0.05 ohms. Is this correct? If we have a dual battery system, should we be using 0.025 ohm resistor (4A total and 2 Amps/battery max if both batteries have the same charge)?
It sounds like you are referring to the input sense resistor (Rcl), for which you can use any value you would like. Refer to the typical applications circuit for the sense resistor reference names.
As for which limit you use, that depends on whether you want to set the limit for both batteries or for one. Just be aware that this determines the total current limit. So, if you limit to 2A and each battery is requesting 2A, the sum of their charge currents will be 2A. So, you might want to use 4A for that reason.
For whichever setting you choose, just make sure that the Rsense and Rilimit resistor values match according to that table. For 2A, Rsense = 50mOhms & Rilimit - 10kOhms. For 4A, Rsense = 25mOhms & Rilimit = open (or short to VCC2).
Thanks for all your help
Once again thanks for all your help. One more issue –
We have a 2 battery system. We are seeing an issue, where if each battery (1 & 2) are not evenly charged or discharged, then the charging will stop whenever the first one gets to 100%. We would definitely prefer if charging would continue until both are fully charged in this case.
Regarding the termination issue, do you have any findings based on my previous suggestions? I would like to know if you can still see the LTC1760 polling the uncharged battery. If so, I would like to see that communication plotted on a scope. It would also be good to read the BatterySystemState() and BatterySystemStateCont() registers from the LTC1760 during this event.
Excuse me if I am asking too many questions.
Going back to emergency shut down mode –
8.3 Emergency Turn-Off All of the PowerPath switches can be forced off by setting the DCDIV pin to a voltage between 8V and 10V. This will have the same effect as a short-circuit event. DCDIV must be less than 5V and VPLUS must decrease below the UVLO threshold to re-enable the PowerPath switches. The LTC1760 can recover from this condition without removing power. Contact Applications Engineering for more information.
It appears that UVLO is internally set between 3v – 5v. VPLUS is the diode OR of BAT1, BAT2 and DCIN voltages.
So if we have these voltages tied , how is VPLUS going to be less than UVLO for LTC1760 to reset from shut down.
Only way would be to remove all power sources physically and re-connect them.
Am I missing something?
No problem, they are good questions!
Yes, you are understanding correctly. You essentially need to reset the IC in order to escape the emergency turn-off state. The datasheet mentions that VPLUS needs to fall below the UVLO threshold and, as you suspected, this means removing all power sources.
However, there is another way to reset the IC not shown in the datasheet (this is where the "contact applications engineering for more information" portion comes into play). I will send you a document that outlines how to reset the part through hardware without removing all of the power.
Can the LTC1760 VPLUS pin be used to power other circuits? If so, what will be the max current?
No, I can't recommend that, unfortunately. Feel free to externally diode-OR the sources, but I'm not sure why you would want to do that since the LTC1760 PowerPath already handles and prioritizes the sources more efficiently than using diodes?
The reason is when you place LTC1760 in Power Off mode via SMBus, the outputs are turned off. We still need a way of powering a small circuit.
Understood, perhaps some external diodes are the answer, then.
We currently diode OR the 3 sources and use that to power our circuit. I thought since VPLUS output is already a diode OR of the 3 sources, I might be able to use it, but apparently not.
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