BQ78350-R1: Current calibration sequence and calculations

Hi Prasanna,

1. There are no changes to the calibration functions in the R2 firmware. In BQStudio, both CC Gain and Capacity Gain are expressed in terms of the sense resistor value (in mohms), so it is a little confusing. So these are not the actual values in the calibration registers. For example CC Gain displays 8.4381 divided by the register value. These registers are also in Xemics floating point format. I am posting an example Python script below that does the floating point conversions.

2. It is best to leave Coulomb Counter Offset Samples at the default value (of 64). It is the number of samples used for the board offset calibration.

3. You don't need to read Coulomb Counter Offset Samples. It is a data flash parameter and is set to 64 by default.

4. I'm not sure if it will ever timeout. 

5. It is possible, but one benefit of the calibration is it can improve accuracy with shunt value variation from board to board.

6. That is correct. Here is a quick example that might be helpful:

Icc = -5000   (in mA)

GGgg from 0xF082 = 0xFED9     -> This is a signed integer, so 0xFED9 = -296

CC Offset = 0  (from 0x4018)

Columb counter samples  = 0x4000  (from 0x4018, little endian format)

 So the calculation for CC Gain is [-5000 / (-296 – 0)] = 16.89

The value displayed in BQStudio is 8.4381 / x, so 8.4381/16.89 = 0.500

 Icc is the current in mA. ADCcc is the code representing the voltage across the sense resistor (-296 * 8.4381uV = 2.5mV).

'''

/* Xemics floating point script
'''
import sys
import time
from time import sleep
import sets
import math

#####################################################

def Dec2Flash(value):
'''

'''
if value == 0:
value += 0.0000001 #avoid log of zero
if value < 0:
bNegative = 1
value *= -1
else:
bNegative = 0

exponent = int( (math.log(value)/math.log(2)) + 1)
MSB = exponent + 128 #exponent bits
mantissa = value / (2**exponent)
mantissa = mantissa / (2**-24)

if (bNegative == 0):
mantissa = int(mantissa) & 0x7fffff #remove sign bit if number is positive

result = mantissa + MSB * 256**3
print hex(result)

def Flash2Dec(value):
'''

'''
exponent = value / (256**3) #exponent is most significant byte
mantissa = value % (256**3)
if (0x800000 & mantissa == 0): #check if number is positive
isPositive = 1
mantissa = 0x800000 + mantissa
else:
isPositive = 0
result = mantissa * 2**(exponent-128-24)
if not(isPositive):
result *= -1
print result

##########################################
# Start of Main Script
##########################################

decDefault = 8.4381
flashDefault = 0x84070275

print "Flash2Dec(0x84070275) = "
Flash2Dec(flashDefault)
print "Dec2Flash(8.4381) = "
Dec2Flash(decDefault)
print "Dec2Flash(16.8762) = "
Dec2Flash(16.8762)