11. Battery Charger (BatMod) Design Guide & Applications Manual For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies OVERVIEW The BatMod is a programmable current source module that is intended for battery charging or simular current source applications. It can be controlled externally to meet a wide range of charging parameters: voltage, current, charge rate and charge time. The BatMod is comparable to the VI-200 voltage source module but with a variable current limit. It has three output pins that differ from the VI-200 converters: Current Control (ITRIM), Voltage Adjust (VTRIM) and Current Monitor (IMON). All of these pins are referenced to the –OUT pin. Although the BatMod is primarily intended for battery charge applications it can be used as a programmable current source for resistive loads or CW laser diodes. The BatMod will not function properly at zero output voltage and current simultaneously. It follows therefore that the current can not be adjusted to zero with a resistive load. Refer to Safe Operating Area Curves on the BatMod data sheet, which can be found at vicorpower.com. Current Monitor (IMON). An output that indicates the amount of current being sourced. It is a linear voltage / current relationship where one volt corresponds to 0% of sourced current and 5 V corresponds to 100% of sourced current. 5 Vdc = 1 Vdc 5 Vdc 0 Amps For DC input / current source applications (Figure 11–1), the BatMod has a similar wide range input rating as the VI-200 Family of voltage converters for 48 and 300 V inputs. BatMods can be used for higher current source applications with a Driver / Booster approach. (Figure 11–2) NOTE: Inductance to the load should be limited to 20 µH to avoid possible loop instabilities. PINOUT DESCRIPTION Current Control (ITRIM). An input which can receive an analog control voltage from 1 – 5 V for adjustment of the sourced current from zero to maximum rating of the BatMod. 100% of Rating DC Input +IN GATE IN GATE OUT –IN BatMod +OUT V TRIM I TRIM I MON + External Control Functions Load – –OUT 100% of Rating = 1 Vdc 0 Amps Figure 11–1 — DC input single module Voltage Adjust (VTRIM). An input for controlling or setting the output setpoint, this is similar to the trim function on the VI-200. (Section 5) A maximum voltage can be set by a fixed resistor or adjusted with an external voltage source. A source voltage referenced to –OUT adjusted from 1.25 – 2.5 V will program a 50 – 100% of rated voltage setting. 2.5 Vdc +IN DC Input Enable/ Disable GATE IN GATE OUT –IN +IN GATE IN GATE OUT –IN Max. Vout BatMod +OUT VTRIM I TRIM I MON –OUT +OUT BatMod Booster –OUT = 1.25 Vdc 50% of Vout +IN GATE IN GATE OUT –IN It is important to note the nominal output voltage for each BatMod type untrimmed. 12 Vout Part # = 15 V actual 24 Vout Part # = 30 V actual 48 Vout Part # = 60 V actual VI-200 and VI-J00 Family Design Guide Page 30 of 98 +OUT BatMod Booster –OUT Figure 11–2 — DC input high power array Rev 3.5 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 + External Control Functions Load – 11. Battery Charger (BatMod) Design Guide & Applications Manual For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies DESIGNING A BATTERY CHARGER Vicor’s BatMod (current source module) enables designers to easily build a compact, lightweight battery charging system with commonly available parts. The BatMod provides programmable output current and output voltage capability. Since the BatMod allows the output voltage and the charge current to be set independently, the system design is greatly simplified. Setting the Charge Current. The charge current can be programmed from 0 to maximum (14.5 A) by applying 1 – 5 V to the ITRIM pin. To determine the voltage required to produce a particular charge current, 10 A for example, use the following formula: ( ( 10 A 4 14.5 A Battery voltage: 12 V Float voltage: 13.8 V Charge current: Adjustable 0 – 14.5 A Setting the Float Voltage. Since the open circuit output of a 12 V BatMod (VI-2x1-CU-BM) is 15 V, a trim resistor (R3) is necessary to set the float voltage of 13.8 V. Steps to determine the value of R3: Solve for VTRIM: ( ) ( ) VFLOAT VNOM VREF = VTRIM Solve for VR5: VREF – VTRIM = VR5 2.5 V – 2.3 V = 0.2 V Solve for IR5: I R5 = VR5 = 0.2 V = 20 µA R5 10 kΩ VTRIM = R3 I R5 2.3 V = 115 kΩ 20 µA A 13.8 V output requires a 115 kΩ resistor. ) + 1 = 3.76 V To set the input voltage at ITRIM to 3.76 V, adjust the potentiometer (R2) appropriately. In Figure 11–3 the configuration will charge the battery at a maximum of 10 A with a 13.8 V float voltage. Other charge rates and float voltages may be similarly calculated. If a fixed charge current is desired, the potentiometer can be replaced with two fixed resistors. In applications requiring tight control over the charging current, D1 can be replaced with a precision reference. Advanced Battery Charger. Many new battery technologies require sophisticated charging and monitoring systems to preserve their high performance and to extend their life. The BatMod serves as an ideal building block for constructing an advanced battery management system, which typically incorporates a microprocessor-based control circuit that is easily adapted for a variety of battery chemistries and monitoring functions. (Figure 11–4) 13.8 V 15 V 2.5 V = 2.3 V Solve for R3: ) Desired Charge Current 4 Maximum Output Current + 1 = ITRIM voltage Basic Battery Charger. Figure 11–3, shows a basic charging circuit with a BatMod for the following system requirements: To maintain the optimum charge on the battery, the control circuit independently adjusts the float voltage and charge current in response to conditions during the charge: the battery’s voltage, current, temperature and pressure, and other pertinent parameters. It can also relay battery status information such as capacity, charge and discharge history, and cause of failure. NOTE: A redundant control or monitoring circuit must be included if failure of the BatMod or its control circuit will result in uncontrolled charging of the battery. Many new battery types are sensitive to these conditions and may result in fire or explosion. With its wide range of outputs, the BatMod offers designers a simple, cost-effective solution to battery charging for all major battery types. VI-200 and VI-J00 Family Design Guide Page 31 of 98 Rev 3.5 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 11. Battery Charger (BatMod) Design Guide & Applications Manual For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies To Front End: AIM, HAM, IAM, or Off-Line Front End BatMod VI-2x1-CU-BM +IN GATE IN ITRIM R5 10 kΩ –IN RITRIM ≈ 50 kΩ REF 2.5 V IMON R3 115 kΩ R2 5 kΩ 1 mA –OUT Figure 11–3 — Basic charging circuit using a current source module (BatMod) +OUT VTRIM ITRIM IMON Control Circuitry • Voltage • Battery Temp. • Ambient Temp. • Other –OUT System Status Figure 11–4 — The BatMod in an advanced battery charging system VI-200 and VI-J00 Family Design Guide Page 32 of 98 R1 820 Ω VTRIM Error Amp GATE OUT 10 mA +OUT Rev 3.5 Apps. Eng. 800 927.9474 vicorpower.com 800 735.6200 D1 5.1 V Zener 12 V