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PDF PS402-01XX Data sheet ( Hoja de datos )
| Número de pieza | PS402-01XX | |
| Descripción | Single Chip Battery Manager - Nickel Chemistries | |
| Fabricantes | Microchip Technology | |
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PS402-01XX
Single Chip Battery Manager - Nickel Chemistries
Features
• Single chip solution for rechargeable battery
management
• Embedded Microchip patented Accuron™
technology provides precise capacity reporting
(within 1%) for all rechargeable battery
chemistries
• User configurable and "learned" parameters
stored in on-chip 128 x 8 EEPROM; fully field
re-programmable via SMBus interface
• Integrating sigma-delta A/D converter accurately
measures:
- Current through sense resistor (15-bits)
- High voltage (18V) battery cells directly
connected to pack voltage input (11-bits)
- Temperature measurement from on-chip
sensor or optional external thermistor
(11-bits)
• Integrated precision silicon time base
• Eight individually programmable input/output pins
that can be assigned as
- Charge control I/O
- Safety function I/O
- SOC LED output drive pins
- General purpose I/O
• Full SMBus v1.1 2-wire host interface
• Microchip firmware in 12 Kbytes of customizable
on-chip OTP EPROM
Pin Description
VDDD
GPIO(4)
GPIO(5)
GPIO(6)
GPIO(7)
SMB-CLK
SMB-DTA
RSV5
RSV6
RSV7
VC(1)
VDDA
VSSA
RSHP
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28 VSSD
27 GPIO(3)
26 GPIO(2)
25 GPIO(1)
24 GPIO(0)
23 RSV1
22 VPP
21 RSV2
20 RSV3
19 RSV4
18 ROSC
17 VREFT
16 VNTC
15 RSHN
28-pin SSOP Package (0.209 mil)
Pin Summary
Pin Name Type
Description
VDDD,
VSSD
Supply Digital supply voltage input,
ground
GPIO(0..7)
I/O Programmable digital I/O
SMB-CLK,
SMB-DTA
I/O SMBus Interface
VC(1)
I Pack voltage input
VDDA, VSSA
Supply
Voltage regulator output
(internally connected to
analog supply input);
ground
RSHP, RSHN I Current sense resistor input
VNTC
I External thermistor input
VREFT
O Thermistor reference
voltage
ROSC
I Internal oscillator bias
resistor
RSV1-7
I Reserved pins
VPP
I OTP programming voltage
2003 Microchip Technology Inc.
DS21766A-page 1
1 page  
2.0 A/D OPERATION
The PS402 A/D converter measures voltage, current
and temperature and integrates the current over time to
measure state-of-charge. The voltage of the entire
pack is monitored, and the pack is calibrated for
accuracy. Using an external sense resistor, current is
monitored during both charge and discharge and is
integrated over time using the on-chip oscillator as the
time base. Temperature is measured from the on-chip
temperature sensor or an optional external thermistor.
Current and temperature are also calibrated for
accuracy.
2.1 Current Measurement
The A/D input channels for current measurement are
the RSHP and RSHN pins. The current is measured
using an integrating method, which averages over time
to get the current measurement and integrates over
time to get a precise measurement value.
A 5 to 600 milli-Ohm sense resistor is connected to
RSHP and RSHN as shown in the example schematic.
The maximum input voltage at either RSHP or RSHN is
+/-150 mV. The sense resistor should be properly sized
to accommodate the lowest and highest expected
charge and discharge currents, including suspend and/
or standby currents.
Circuit traces from the sense resistor should be as
short as practical without significant crossovers or
feedthroughs. Failure to use a single ground reference
point at the negative side of the sense resistor can
significantly degrade current measurement accuracy.
The OTP EPROM value NullCurr represents the zero-
zone current of the battery. This is provided as a
calibration guard band for reading zero current.
Currents below +/- NullCurr (in mA) limit are read as
zero and not included in the capacity algorithm
calculations. A typical value for NullCurr is 3 mA, so
currents between -3 mA and +3 mA will be reported as
zero and not included in the capacity calculations.
PS402-01XX
The equation for current measurement resolution and
sense resistor selection is:
9.15 mV / RSENSE (milli-Ohms) = Current LSB
(Minimum current measurement if > NullCurr)
Current LSB x 16384 = Maximum current
measurement possible
In-circuit calibration of the current is done using the
SMBus interface at time of manufacture to obtain
absolute accuracy in addition to high resolution. The
current measurement equation is:
I(ma)=(I_A/D – COCurr – COD) * CFCurr /16384
where:
I_A/D is the internal measurement.
COCurr is the "Correction Offset for Current" which
compensates for any offset error in current
measurement, stored in OTP EPROM.
CFCurr is the "Correction Factor for Current" which
compensates for any variances in the actual sense
resistance over varying currents, stored in OTP
EPROM
Figure 2-1 shows the relationship of the COCurr and
CFCurr values.
FIGURE 2-1:
A/D Output
COCurr AND CFCurr
VALUE RELATIONSHIP
Ideal A/D
Response
Actual A/D
Response
CFCurr
COCurr
Current Input
2003 Microchip Technology Inc.
DS21766A-page 5
5 Page 
4.0 CAPACITY MONITORING
The PS402 internal CPU uses the voltage, current and
temperature data from the A/D converter, along with
parameters and cell models from the EEPROM and
OTP EPROM, to determine the state of the battery and
to process the SBData function instruction set.
By integrating measured current, monitoring voltages
and temperature, adjusting for self-discharge and
checking for end-of-charge and end-of-discharge
conditions, the PS402 creates an accurate fuel gauge
under all battery conditions.
4.1 Capacity Calculations
The PS402 calculates state-of-charge and fuel gauging
functions using a ‘coulomb counting’ method, with
additional inputs from battery voltage and temperature
measurements. By continuously and accurately
measuring all the current into and out of the battery
cells, along with accurate three dimensional cell
models, the PS402 is able to provide run-time accuracy
with less than 1% error.
The capacity calculations consider two separate states:
charge acceptance or capacity increasing (CI) and
discharge or capacity decreasing (CD). The CI state
only occurs when a charge current larger than OTP
EPROM NullCurr value is measured. Otherwise, while
at rest and/or while being discharged, the state is CD.
Conditions must persist for at least NChangeState
measurement periods for a valid state change between
CD and CI. A minimum value of 2 is suggested for
NChangeState.
Regardless of the CI or CD state, self-discharge is
also calculated and subtracted from the integrated
capacity values. Even when charging, there is still a
self-discharge occurring in the battery.
To compensate for known system errors in the capacity
calculations, a separate error term is also continuously
calculated. This term is the basis for the SBData value
of MaxError. Two error values are located in OTP
EPROM. The CurrError value is the inherent error in
current measurements and should be set based on the
selection of a sense resistor and calibration results.
The SelfDischrgErr value is the error in the parameter
tables for self-discharge and depends on the accuracy
of the cell chemistry model for self-discharge.
PS402-01XX
Since the PS402 electronics also drain current from the
battery system, another OTP EPROM value allows
even this minor drain to be included in the capacity
calculations. The PwrConsumption value represents
the drain of the IC and associated circuitry, including
additional safety monitoring electronics, if present. A
typical value of 77 represents the PS402's nominal
power consumption of 300 µA.
The total capacity added or subtracted from the battery
(change in charge) per measurement period is
expressed by the following formula:
∆Charge = Σi∆t (the current integrated over time)
- CurrError (Current Meas. Error)
- PwrConsumption * ∆t (PS402 IDD)
- % of Self-Discharge * FCC
- SelfDischrgErr (Self-Disch. Error)
The error terms are always subtracted, even though
they are +/- errors, so that the fuel gauge value will
never be overestimated. Current draw of the PS402
and the self-discharge terms are also always
subtracted. The SBData value MaxError is the total
accumulated error as the gas gauge is running.
The battery current will be precisely measured and
integrated at all times and for any current rate, in order
to calculate total charge removed from or added to the
battery. Based on lookup table access, the capacity is
adjusted with self-discharging rates depending on
actual capacity and temperature, residual capacity
corrections depending on the discharging current rate
and temperature, and charge acceptance depending
on SOC, charging current rate and temperature.
4.2 Discharge Termination and
Capacity Relearn
Discharge capacity is determined based on the End-
Of-Discharge (EOD) voltage point. This voltage can be
reached at different times based on the discharge rate.
The voltage level at which this point occurs will also
change depending on the temperature and discharge
rate, since these factors affect the voltage curve
and total capacity of the battery. The EOD voltage
parameter table predicts the voltage point at which this
EOD will be reached based on discharge rate and
temperature.
2003 Microchip Technology Inc.
DS21766A-page 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet PS402-01XX.PDF ] | |
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