PS401-I/SS Microchip Technology, PS401-I/SS Datasheet - Page 6

• Manufacturer Part Number: PS401-I/SS
• Description: IC FUEL GAUGE BATTERY MGR 28SSOP
• Manufacturer: Microchip Technology

Specifications of PS401-I/SS

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measurements are the VC(1) to VC(4) pins. Measure-
2.3
The A/D input channels for cell and pack voltage
ments are taken each measurement period when the
A/D is active. The maximum voltage at any V
pin is 19V absolute, but voltages above 18V are not
suggested. The individual cell voltages are measured
with an integration method to reduce any sudden spikes
or fluctuations. The A/D uses an 11-bit Resolution mode
for these measurements.
Only one cell voltage input is read per measurement
period, therefore in multi-cell configurations, it may take
multiple measurement periods to read all inputs. This
could be further extended by the use of Run mode,
where A/D measurements are not activated every
measurement period, depending on the configuration
of
Section 3.0, Operational Modes for additional informa-
tion.) For Li Ion, Li-based or even Lead-Acid applica-
tions, up to four (4) series cell voltages may be
monitored individually. The highest voltage cell of the
stack must be connected to VC(1).
For some applications, the actual cell stack arrange-
ment can be altered accordingly. The PS401 voltage
inputs pins (V
to 18V each. Therefore, cell arrangements can be
combined
thresholds can be adjusted. For example, a 2-cell Li Ion
pack could actually be connected as a single 7.2V cell
instead of two 3.6V cells. The values for the cell volt-
ages would all be doubled and only the VC(1) input pin
would be used.
Each V
divider to reduce the external voltage input to a range
that the internal A/D circuit can accommodate (150 mV
maximum). These dividers are set based on a cell
voltage range of 4.5 Volts maximum.
The impedance at each V
100 kOhms, but is only connected to ground (via the
V
occurring. This corresponds to an insignificant amount
of capacity drained through this circuit during the brief
voltage measurement period.
PS401
DS40238B-page 6
SSA
SampleLimit
pins) when the actual voltage measurement is
CELL
Voltage Measurements
x input circuit contains an internal resistive
and
CELL
x pins) are capable of measuring up
the
and
corresponding
NSample
CELL
x input is roughly
values.
cell
CELL
voltage
x input
(See
2.3.1
Since accurate measurement of pack voltage and cell
voltages are critical to performance, the voltage
measurements
impedance in the power path that might affect the
voltage measurements.
The first compensation point is the current sense
resistor. This sense resistor affects the measured
voltage of the lowest cell in a Li Ion configuration, since
the ground reference point for the measurement is on
the side of the current sense resistor farthest from the
lowest cell.
The OTP EPROM value PackResistance is used to
compensate for additional resistance that should be
removed.
The equation for the compensation value (in ohms) is:
This requires modification of overall voltage SBData
function to compensate for pack resistance and shunt
resistance of current sense resistor. Thus, the previous
voltage equation is modified to:
Figure 2-2 illustrates the compensations provided by
the PackResistance value. The heavy traces are the
portions of the circuit represented by the resistance.
The voltage measurement equation is:
COVPack is the "Correction Offset for Pack Voltage"
which compensates for any offset error in voltage
measurement (since the offset of the A/D is less than
the voltage measurement resolution of +/- 16.5 mV, the
COVPack value is typically zero).
PackResistance = Trace resistance * 65535
(This is a 2-byte value so the largest value is
1 ohm.)
SBData Voltage value = VC(1) + Measured
Current (mA) * PackResistance / 65535)
V (mV) = (V_A/D - COVPack) x CFVPack / 2048
where:
V_A/D is the internal measurement output.
IMPEDANCE COMPENSATION
can
be
 2003 Microchip Technology Inc.
compensated
for
any