Datasheet
www.ti.com
Appendix A Theory of Operation for HPA495 Calibration Board
The HPA495 multi-station tester board consists of three sections: a communication, control, and
temperature section, a voltage supply section, and a current supply section. The board is designed to be
temperature-independent. The board can be controlled through an SMBus via an EV2x00 interface, or
through a user-designed custom interface supporting I
2
C. For the schematic, see Appendix B. For cell
voltage references, see TBD.
The communication, control, and temperature section consists of two ICs, a TMP100NA Digital
Temperature Sensor with I
2
C interface, and a TPIC2810D 8-bit LED Driver with I
2
C interface. The
TMP100NA is used to report the board temperature through SMBus or I
2
C. The TPIC2810D is used not
only to control board status LEDs, but also to enable and disable the voltage and current sections by
controlling two optoisolators. Power for these two devices (5 VDC) is supplied from the EV2x00 or custom
user interface from the computers USB port. Headers have been provided on the board for the addition of
an external I
2
C temperature sensor, an additional I
2
C communication port, and external status LEDs.
The voltage supply section consists of a TL317 100 mA Adjustable Positive Voltage Regulator set to
supply 20 VDC, a REF5050 +5V Precision Voltage Reference, a H11A1SM optoisolator, a 2N7002
N-channel FET, two OPA4244 quad op amps, four FMMT491A general purpose NPN transistors, and
various capacitors, and resistors. Power is supplied to the voltage supply section with a 24V, 500mA wall
mounted power supply. When power is supplied to the voltage supply section, the Voltage Supply LED will
light, the TL317 will supply 20 V, and the REF5050 will supply a 5 V reference. The REF5050 is a high
precision reference with very low temperature drift. The voltage divider formed by R11, R10, and R18 will
cause 3.7 V to appear on the positive input of the OPA4244 error amps. R11 is a high precision 0.5% 10
PPM resistor. R10 and R18 are high precision 0.1% 25 PPM resistors. These values are critical to ensure
3.7 V is supplied to the positive input of the error amps. Four of the eight error amps in the two OPA4244
ICs are utilized to create four different voltages representing the four voltages in a 4s battery stack. For
example, R33 and R34 are used in a non-inverting configuration with the error amp to produce a 7.4 V
output. The four networks produce 3.7 V, 7.4 V, 11.1 V, and 14.8 V. The FMMT491A transistors provide
current boost. The H11A1SM optoisolator and 2N7002 FET are used to enable or disable the voltage
supply. An enable or disable command is sent via SMBus from the EV2x00 or user-supplied I
2
C controller
to the TPIC2810D LED driver which then enables or disables the appropriate output pin which is
connected to the H11A1SM optoisolator. This causes the optoisolator to turn on or turn off the 2N7002
FET which in turn will ground or unground the positive input of the OPA4244 error amp. Grounding the
input will cause the output of the error amp to go to 0 V, which will disable the voltage supply. The
transition of the TPIC2810D output pin will also cause the Voltage On LED to turn on or off.
The current supply section consists of a REF3133 +3.3 V Precision Voltage Reference, a H11A1SM
optoisolator, a 2N7002 N-channel FET, a OPA2335 dual op amp, a IRF3709 FET, a 20-mΩ sense
resistor, two 1-Ω 2-W resistors, and various capacitors and resistors. Power is supplied to the current
supply section with a 5-V, 3-A wall mounted power supply. When power is supplied to the current supply
section, the Current Supply LED will light. Current flows from the power supply, through the IRF3709 FET,
through the 20-mΩ sense resistor, through the two parallel 1-Ω, 2-W heat dissipating resistors, through a
user-supplied reference meter, through the sense resistor in the unit under test, and back to the wall
mounted power supply. This current induces a voltage across the 20-mΩ sense resistor, which is then
amplified by the differential amplifier (U7:B). The voltage from the differential amplifier is then fed back into
the error amp (U7:A). The error amp gets its reference voltage from the REF3133 +3.3-V voltage
reference. The REF 3133 is a high precision reference with very low temperature drift. The output of the
error amp drives the gate of the IRF3709 FET. This feedback arrangement ensures that the current in the
current loop remains exactly the configured value, regardless of the temperature. The current setting can
be configured for three different settings of 0.5 A, 1 A, or 2 A, depending on the setting of jumpers J4, J5,
J6, and J7. These jumpers control the input resistance to U7:B; thus, adjusting the feedback gain of the
amplifier. The H11A1SM optoisolator and 2N7002 FET are used to enable or disable the current supply.
An enable or disable command is sent via the SMBus from the EV2x00 or user-supplied I
2
C controller to
the TPIC2810D LED driver which then enables or disables the appropriate output pin which is connected
to the H11A1SM optoisolator. This causes the optoisolator to turn on or turn off the 2N7002 FET which in
turn will ground or unground the gate of the IRF3709 FET. Grounding the gate will turn off the FET and
disable the current supply. The transition of the TPIC2810D output pin will also cause the Current On LED
to turn on or off.
29
SLUU397A– February 2011– Revised May 2011 Theory of Operation for HPA495 Calibration Board
Submit Documentation Feedback
Copyright © 2011, Texas Instruments Incorporated