LM5066I: Telemetry wrong values

Hi Michael,

Can you let us know the value of sense resistor (RS) in your design. Table 47 represents the case with sense resistor (RS) =  1mOhm

Best Regards, Rakesh

Hi Rakesh,

we are using RS = 15mOhm

Hi Michael,

Ok. Please use as per Table 48

Yes i am using Table 48 and the current and power measurement are wrong.

Its a 2x factor too small. For example the equation returns 50mA instead of 100mA.

The rows should be swapped

Hi Michael,

Ok Understood.

Please share the coefficients you used for 15mOhm to check at our end.

Also, how are the measurements at half or near full load current.?

Best Regards, 

Rakesh

Hi Rakesh,,

the measurements have the same error factor with half and full current.

This is my code:

def equation(self, m, Y, b, R):
    return 1/m * (Y * math.pow(10, -R) - b)

#RS=15mOhm

self.AVG_IIN = self.equation(7645 * self.RS, avg_block_read.AVG_IIN, 100, -2) *1000#mA
self.AVG_VOUT = self.equation(4602, avg_block_read.AVG_VOUT, 500, -2)  # V
self.AVG_VIN = self.equation(4617, avg_block_read.AVG_VIN, -140, -2) # V
self.AVG_PIN = self.equation(860.6 * self.RS, avg_block_read.AVG_PIN, -965, -3)#W
self.AVG_TEMPERATURE = self.equation(16000, avg_block_read.TEMPERATURE, 0, -3)  # °C
self.READ_VAUX = self.equation(13774, value_vaux, 73, -1) * self.VAUX_SLOPE + self.VAUX_OFFSET  #V
self.READ_PIN_PEAK = self.equation(860.6 * self.RS, value_peak, -965, -3)  # W

My CL is connected to VDD but i use here the CL=GND values because the values are incorrect if i use CL=VCC

Best regards,

Michael

Hi Michael,

When CL=VDD; m value = 15076 × RS = 226140 for Rs = 15m Ohm

Take care to adjust the exponent coefficient, R, such that the value of m remains within the range of –32768 to 32767. For example, if a 5-mΩ sense resistor is used, the correct coefficients for the READ_IIN command with CL = VDD would be m = 7553, b = –65, R = –1.

Similarly, for your case

m = 22614; b = -50.3 and R = -1

try with the above coefficients for CL=VDD and confirm the current measurement.

Best Regards, 

Rakesh

Hi Rakesh,

When CL=VDD; m value = 15076 × RS = 226140 for Rs = 15m Ohm the Power and current measurement are wrong by factor 2.

When CL=GND; m value = 7645 × RS = 114675 for Rs = 15m Ohm the Power and current measurement are correct. (But my hardware PIN CL is at VCC)

So the table coefficients are swapped. Can you reproduce it on your side too?

Hi Rakesh,

here is the results:

I have a multimeter measuring 120mA and 107mA comes very close, but 550mA is out of range.

Can you confirm this on your side?

Hi Michael,

R should be -1

Can you pls check now.

Best Regards, 

Rakesh

Hi Rakesh,

now it works, thank you very much.

I didnt saw this:

:"Take care to adjust the exponent coefficient, R, such that the value of m remains within the range of –32768 to 32767. For example, if a 5-mΩ sense resistor is used, the correct coefficients for the READ_IIN command with CL = VDD would be m = 7553, b = –65, R = –1."

Hi Rakesh,

so i am still facing the  issue.

The current i am measuring is 17mA and 7.09mA is wrong.

It doenst matter if i divide by than the result is the same too:

If i increase the current, i am measuring 110 mA and this is what i am getting:

If i look into the example "5-mΩ sense resistor is used, the correct coefficients for the READ_IIN command with CL = VDD would be m = 7553, b = –65, R = –1"

m = 15076 * 5 /10= 7538 and it is not 7553

b= -503.9/10 = -50.39 and it is not -65

R =-1

How can i corretly measure current? Or how do i normalize it corretly?

EDIT:

so if i calculate it per hand it would be like this:

y = 0.93 * x + 6.77 -> whew y: mA and x: ADC digits

turning it around:

x = 1/0.93 * (y - 6.77)

m = 1/0.93 

b = -6.77

R = 0 (dont need anything here)

ok Michael