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Application Note

Rev. 8088A-AVR-09/07

AVR451: BC100 Hardware User's Guide

Features

• Tripple buck converter for battery charging.

- Low voltage/current (max 20V/1A).

- Medium voltage/current (max 20V/2.5A).

- High voltage/current (max 38V/5A).

• Battery (dis)charging using ATtiny261/461/861 or ATtiny25/45/85.

- Uses DC supply voltage and buck converter to charge batteries.

- Powers application/own circuits when line power is missing.

• Support for two battery packs.

- Relay controlled enabling of battery packs.

• Host controller (ATmega644).

- Interface MCU responsible for charging.

- Support for DB101 graphical display board.

- Monitor voltages and currents on the board.

1 Introduction

The BC100 is reference design/development kit that targets especially battery

charging. As the kit is general in nature it can be used to charge various battery

types, as long as the requirements to charging voltage and currents are within the

output range that the kit offers (1.2V to 38V, max 5A).

The kit can be used to develop applications such as battery chargers, battery

backup, Un-interruptable power supply, switch mode power supply and other.

Figure 1-1. BC100 hardware.

Summary of content (13 pages)

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AVR451: BC100 Hardware User's Guide Features • Tripple buck converter for battery charging. - Low voltage/current (max 20V/1A). - Medium voltage/current (max 20V/2.5A). - High voltage/current (max 38V/5A). • Battery (dis)charging using ATtiny261/461/861 or ATtiny25/45/85. - Uses DC supply voltage and buck converter to charge batteries. - Powers application/own circuits when line power is missing. • Support for two battery packs. - Relay controlled enabling of battery packs. • Host controller (ATmega644).
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Hardware overview The BC100 consists of two main parts: the battery charging circuits and circuits related to the ATmega644 board controller. The battery charger circuits can be used without interaction with the board controller. The charger circuits has two AVR® sockets, one for the ATtiny261/461/861 and on for ATtiny25/45/85. From factory the kit is delivered with both an ATtiny861 and an ATtiny85. Both of these can control the buck-converts on the board, but not at the same time.
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AVR451 3 Main hardware blocks The blocks of the BC100 used for battery charging are described below. For more details on parts of the design not described below, please refer to the schematics. 3.1 Buck converters The buck converters are used to generate a given output voltage that can be used to e.g. charge batteries (or even control the speed of a DC motor).
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3.2 Shunt network A shunt resistor (70mOhm, 1%) is placed in the charge/discharge path of the battery. The shunt resistor is used to measure the current that flows in and out of the battery. The ATtiny devices are measuring the voltage over the shunt (differentially ADC reading) and can use this information to calculate the current flow and adjust the charge voltage/current accordingly, or terminate the charging.
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AVR451 The maximum input voltages to the ATtiny device must be below the supply voltage of the ATtiny, and the differential voltage over the shunt (resistor dividers) must be below the ADC’s voltage reference, which is 2.5V (0.1% accuracy). If the differential voltage is low the internal gain stage of the ATtiny can be enabled to get better readings. 3.3 Electronic load The BC100 features two electronically controlled constant current loads (adjustable).
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Always keep the temperature of the FETs (Q404 and Q405) and the resistors (R444 and R445) below a reasonable temperature (very warm is ok, untouchable is bad). The equations below can be used to determine the maximum currents for the load resistors and FET transistors – still, keep well below these values. Equation 3-1. Maximum current in the resistor in the electronic load. I res, max = 2W = 4.47 A 100 mΩ Equation 3-2. Maximum current in the FET transistor in the electronic load.
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AVR451 4.2 RS232C connector A RS232C connector is available to connect the BC100 to e.g. a PC. The RS232C connector is connected to the ATmega644 board controller (USART0) and can be used interact with or as a gateway to the ATtiny AVRs connected to the charging circuits. 4.3 Battery terminals The charger can connect to two individual battery packs, which can be connected to the board through two sets of screw-terminals.
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Note that ATmega644 firmware for communicating with the DB101 is not included in the firmware distributed with this application note. Please refer to the DB101 documentation for more information about the DB101 connectors. 4.5 Programming and debugging headers The ATtinyx61 and ATtinyx5 can be ISP programmed through their respective ISP/dW 6 pin headers (2.54mm). The same connectors can be used for debugging using DebugWire.
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AVR451 ATmega644 board controller it can be programmed regardless of the state of the SPI lines. If SPI communication is used between a ATtiny and the ATmega644 a way to ensure that programming is successful, is to erase the ATmega644 first, next program the ATtiny and finally program the ATmega644.
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Designator Use and settings J407/408 Connects the either “BUCK-A”, BUCK-B” or “BUCK-C” converter output to the battery terminals (through shunt resistor network). The jumpers should be mounted in pairs due to potentially high currents. Never place the jumpers so that the output from the different buck converters are shorted, this may damage the buck converters. Figure 4-2. Location of jumpers on the BC100. J402 J400/401 J403 J404 J302 J406 J405 4.
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AVR451 5 Preprogrammed firmware The BC100 comes with the firmware from application note AVR458 “Charging Lithium-Ion Batteries with ATAVRBC100” programmed in the ATtiny861. The ATtiny85, is programmed with a small program that does nothing but putting the device in Power Down mode. The ATmega644 is programmed with a firmware that controls the power switch on the board, but other wise do nothing. The source code for this firmware is distributed with this application note.
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Disclaimer Headquarters International Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: 1(408) 441-0311 Fax: 1(408) 487-2600 Atmel Asia Room 1219 Chinachem Golden Plaza 77 Mody Road Tsimshatsui East Kowloon Hong Kong Tel: (852) 2721-9778 Fax: (852) 2722-1369 Atmel Europe Le Krebs 8, Rue Jean-Pierre Timbaud BP 309 78054 Saint-Quentin-enYvelines Cedex France Tel: (33) 1-30-60-70-00 Fax: (33) 1-30-60-71-11 Atmel Japan 9F, Tonetsu Shinkawa Bldg.
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