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# CN0510: Handling Battery with Higher Voltages

Category: Hardware
Software Version: N/A

Dear Analog Devices Engineers,

I am currently studying the possibility to convert the design described in CN0510 circuit note to handle batteries that have higher voltages, for EIS purposes (measure battery impedance). Typical example would be 12V battery, which I think not supported in the current evaluation board (EVAL-AD5941BATZ).  According to the circuit diagram from EVAL-AD5941BATZ, the excitation signal was generated through the pin CE0, which drives the Darlington transistor pair, connected to a battery. This topology directly draws the current from the battery under test, I am not sure how many V can it takes. I think that it probably cannot support a battery up to 12V. Is there any way we can develop a solution to measure batteries with 12V or even higher?

My guess is that we would need to design another type of switching circuit rather than using Darlington transistor pair.

Thanks.

Parents
• Hi,

TIP31BG is used in the Darlington pair which allows VCE upto 10V (since its Vcc = 10V). For batteries with 12V, some other power transistor with VCC >=12V must be used for the Darlington pair.

• TIP31A - Complementary Silicon Plastic Power Transistors (onsemi.com)

Says TIP31BG can stand max of 80 VDC. 12 should be no problem. No?

• Hi,

• The TIP31BG is an 80V device, so that’s one limitation.
• The limit is the voltage ratings on capacitors C36/37/38/39 used in EvalAD5940BATZ board which are 10V devices.

Hence VCE voltage is restricted to 10V max.

• OK - although those caps are effectively connected in series and might take 20 volts.  Looking at it, I now wonder about the ADG636. The absolute max input voltage is specified as VDD +0.3 volts. During connection or disconnection of a battery, it might see a momentary spike as high as the battery terminal voltage. Is there any built-in protection for this?

• There is a low pass filter (marked by LPF0 in schematic) at the input of ADG636 that doesn't allow spike voltage to reach the IC.

Yoi may refer to EVALAD5940BATZ schematic here: CN0510 User Guide [Analog Devices Wiki] for circuit at input of ADG636.

• Sorry. I don't see how this protects the 636.  I can understand that this prevents sustained voltage from appearing at "sense_p" but it seems to me that C39 and R2 actually form a high pass filter that would provide a nice transient into pin 11 of the 636.

The situation I am thinking of is where F- S- are connected to the battery (and hence AGND) and then you connect S+ F+..  The point SNS_P momentarily rises to the full battery voltage relative to AGND.  As C9 and C36 charge up, this voltage difference decays.

I think the only thing that protects against this is the 1K resistor R8 and any built-in protection diodes on the inputs of the 636. Looking at the spec sheet, I see that there are supposed to be such diodes. Max current spec is 20 ma for 1 ms. So perhaps the inputs are protected up to about 20 volts.

• I am telling about the LPF0 wire connected to input of ADG636, not the series cap.

You may search for LPF0 in schematic.

• In the schematic that I have, there is no connection from LPF0 to ADG636.

Perhaps you mean via 2.2 Meg resistors R2 and R3?

• LPF is highlighted:

• Yes, I see. My point is that since the connection to ADG636 inputs via 2.2 M resistors, it offers no protection against fast transients coupled via C38 or C39.  I think the 1K series-connected resistors R7 and R8 combined with the built-in protection diodes produce the protective effect.  The only question is how much voltage this can withstand. I was guessing 20 volts, which means a 24-volt battery might be too much.

• Hi,

I wish to direct you to this document: Using Electrochemical-Impedance Spectroscopy to Image Failures in Hydrogen Fuel Cells | Analog Devices

which shows how current excitation can be extended in CN0510.