ISL28022_15 Datasheet, PDF (17/32 Pages) Intersil Corporation – Precision Digital Power Monitor

ISL28022
BUS VOLTAGE REGISTER 02H (READ-ONLY)
The bus voltage register is where the DPM reports the measured
value of the V_BUS. There are three scale ranges possible
depending on the BRNG setting controlled from the configuration
register(00H).
Tables 12 through 14 on page 16 are the weight bits for each
BRNG setting. The binary value recorded in the Bus Voltage
Register is translated to a decimal value in the same way as the
shunt voltage register is converted to a decimal value.
 ^{  Vbus}
 ¹⁵

Bit_nBit_Weight _n

 _{ Vbus}

LSB
^{n  2}

(EQ. 1)
Equation 1 is the mathematical equation for converting the
binary V_BUS value to a decimal value. N is the bit number. The
LSB value for the V_BUS measurement equals 4mV across all bus
range (BRNG) settings.
CNVR: Conversion Ready (Bit 1)
The conversion ready bit indicates when the ADC has finished a
conversion and transferred the reading(s) to the appropriate
register(s). The CNVR is only operable when the DPM is set to one
of three trigger modes. The CNVR is at a high state when the
conversion is in progress. The CNVR transitions and remains at a
low state when the conversion is complete.
The CNVR bit is initialized or reinitialized in the following ways:
1. Writing to the configuration register.
2. Reading from power register.
OVF: Math Overflow Flag (Bit0)
The Math Overflow Flag (OVF) is a bit that is set to indicate the
current or power data being read from the DPM is over-ranged
and meaningless.
CALIBRATION REGISTER 05H (READ/WRITE)
To accurately read the current and power measurements from
the chip, the calibration register needs to be programmed.
The calibration register value is calculated as follows:
1. Calculate the full-scale current range that is desired. This is
calculated using Equation 2. R_shunt is the value of the shunt
resistor. V_SHUNT is the full-scale setting that is desired. In
most cases, it is the PGA full-scale range (320mV, 160mV,
80mV and 40mV) that the DPM is programmed to.
Current _FS
Vshunt _FS
R _shunt
(EQ. 2)
2. From the current full-scale range, the current LSB is
calculated using Equation 3. Current full-scale is the outcome
from Equation 2. ADC_res is the resolution of shunt voltage
reading. The value is determined by the SADC setting in
configuration register. SADC setting equal to 3 and greater
will have a 15-bit resolution. The ADC_res value equals 2¹⁵ or
32768.
Current _LSB
Current _FS
ADC _res
(EQ. 3)
3. From Equation 3, the calibration resister value is calculated
using Equation 4. The resolution of the math that is processed
internally in the DPM is 4096 or 12 bits of resolution. The
V_SHUNT LSB is set to 10µV. Equation 4 yields a 16-bit binary
number that can be written to the calibration register. The
calibration value can only be 15 bits due to the ADC_res value.
Bit 0 of the calibration register is fixed to a value of 0. The
calibration register format is represented in Table 15.
  ^CalRegval
integer



Math _resVshunt _LSB
Current_LSBR_shunt


CalReg_val integer^{}_{Curren0t.0L}⁴_S⁰_B⁹_{R6shunt}^{}
(EQ. 4)
CURRENT REGISTER 04H (READ-ONLY)
Once the calibration register (05h) is programmed, the output
current is calculated using Equation 5:
Current
 ^{   15}

Bit_n Bit_Weight _n

 _{ Current}

LSB
^{n  0}

(EQ. 5)
Bit is the returned value of each bit from the current register
either 1 or a 0. The weight of each bit is represented in Table 16.
n is the bit number. The current LSB is the value calculated from
Equation 3.
POWER REGISTER 03H (READ-ONLY)
The Power register only has meaning if the calibration register
(05H) is programmed. The units for the power register are in
watts. The power is calculated using Equation 6:
Power
 ¹⁵

 ^{  }

^{n  0}
Bit_n Bit_Weight _n
 _{ Power}

LSB^5000

(EQ. 6)
Bit is the returned value of each bit from the power register either
1 or a 0. The weight of each bit is represented in Table 17. n is
the bit number. The power LSB is calculated from Equation 7:
Power _LSB Current _LSBVbus _LSB
(EQ. 7)
If V_BUS range, BRNG, is set to 60V, the power equation in
Equation 6 is multiplied by 2.
THRESHOLD REGISTERS
The Shunt Voltage or V_BUS threshold registers are used to set the
Min/Max threshold limits that will be tested versus V_SHUNT or
V_BUS readings. Measurement readings exceeding the respective
V_SHUNT or V_BUS limits, either above or below, will set a register
flag and perhaps an external interrupt depending on the
configuration of the interrupt enable bit (INTREN) in register 09h.
The testing of the ADC reading versus the respective threshold
limits occurs once per ADC conversion.
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FN8386.7
October 2, 2015