2.2.1 Subsystem Description

Figure 3 shows the block diagram of the MSP430F5510 daughterboard subsystem.

The daughtercard subsystem has the following features:

• The I²C USCI module within the MSP430F5510 is used to implement the SMBus protocol for communication with the battery fuel gauges.
• A 1-to-2 demultiplexer (demux), TS3A24157, is used to separate the SMBus clock (SCL) and data (SDA) lines for the two batteries ^[15]. During the manufacturing process, all of the fuel gauges for a particular battery series are programmed to the same SMBus slave address. The advantage of using a demux is that one microcontroller with one I²C/SMBus USCI module can be used to communicate with multiple fuel gauges within multiple smart-batteries.
• The MSP430F5510 outputs voltage and current PWM signals at a frequency of 20 kHz to control the power delivered by the DC/DC converters on the power stage subsystem.
• The on-chip 10-bit ADC is used to convert voltage and current signals from the batteries. The voltage from the battery is divided down from the wide-input range to the ADC range by means of a resistor-divider circuit on the MSP430F5510 daughterboard. The current is fed into a shunt resistor on the power-stage board, and the resulting voltage is fed into the ADC channels directly.
• Eight status LED indicators; seven are software programmable, and one indicates power-on status.
• Two sets of power resistors for discharging two batteries independently. The discharge circuitry can be turned on or off by the microcontroller to calibrate battery pack voltages. Section 9 has details on setting up these circuits.
• Fan control output to power a heat venting circulation fan on or off.
• Two options to program the software on the MSP430F5510 daughterboard:
  • 14-pin JTAG interface (four-wire) for connecting the flash emulation tool (FET)
  • 6-pin Spy-Bi-Wire interface (two-wire) for connecting the eZ430 emulator
• Three options to power the MSP430F5510 daughterboard:
  • JTAG interface (voltage level programmable in the integrated development environment (IDE) options)
  • eZ430 emulator interface (supply voltage fixed at 3.6 V)
  • The charger board supply power (approximately 10 V), which is routed through the TPS71533 LDO to supply 3.3 V to the MSP430F5510 ^[16]. For a wider input supply range up to 50 V, the TPS79801 LDO can also be used to supply 3.3 V ^[17].