19-0100; Rev 5; 4/02 KIT ATION EVALU E L B A IL AVA NiCd/NiMH Battery Fast-Charge Controllers The MAX712/MAX713 fast-charge Nickel Metal Hydride (NiMH) and Nickel Cadmium (NiCd) batteries from a DC source at least 1.5V higher than the maximum battery voltage. 1 to 16 series cells can be charged at rates up to 4C. A voltage-slope detecting analog-to-digital converter, timer, and temperature window comparator determine charge completion. The MAX712/MAX713 are powered by the DC source via an on-board +5V shunt regulator. They draw a maximum of 5µA from the battery when not charging. A low-side current-sense resistor allows the battery charge current to be regulated while still supplying power to the battery’s load. The MAX712 terminates fast charge by detecting zero voltage slope, while the MAX713 uses a negative voltage-slope detection scheme. Both parts come in 16pin DIP and SO packages. An external power PNP transistor, blocking diode, three resistors, and three capacitors are the only required external components. For high-power charging requirements, the MAX712/ MAX713 can be configured as a switch-mode battery charger that minimizes power dissipation. Two evaluation kits are available: Order the MAX712EVKIT-DIP for quick evaluation of the linear charger, and the MAX713EVKITSO to evaluate the switch-mode charger. ________________________Applications Battery-Powered Equipment Laptop, Notebook, and Palmtop Computers Handy-Terminals Cellular Phones Features ♦ Fast-Charge NiMH or NiCd Batteries ♦ Voltage Slope, Temperature, and Timer Fast-Charge Cutoff ♦ Charge 1 to 16 Series Cells ♦ Supply Battery’s Load While Charging (Linear Mode) ♦ Fast Charge from C/4 to 4C Rate ♦ C/16 Trickle-Charge Rate ♦ Automatically Switch from Fast to Trickle Charge ♦ Linear or Switch-Mode Power Control ♦ 5µA (max) Drain on Battery when Not Charging ♦ 5V Shunt Regulator Powers External Logic Ordering Information PART TEMP RANGE PIN-PACKAGE MAX712CPE 0°C to +70°C 16 Plastic DIP MAX712CSE MAX712C/D MAX712EPE 0°C to +70°C 0°C to +70°C -40°C to +85°C 16 Narrow SO Dice* 16 Plastic DIP MAX712ESE MAX712MJE -40°C to +85°C -55°C to +125°C 16 Narrow SO 16 CERDIP** Ordering Information continued at end of data sheet. *Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883. Typical Operating Circuit Portable Consumer Products Portable Stereos Cordless Phones Q1 2N6109 DC IN R2 150Ω C4 0.01µF R1 Pin Configuration TOP VIEW VLIMIT 1 16 REF BATT+ 2 15 V+ PGM0 3 14 DRV PGM1 4 THI 5 MAX712 MAX713 9 DIP/SO C1 1µF PGM2 VLIMIT BATT+ REF R3 68kΩ MAX712 MAX713 BATTERY C3 10µF TEMP 12 BATT- 10 PGM3 TEMP 7 FASTCHG 8 D1 1N4001 V+ 13 GND 11 CC TLO 6 DRV THI WALL CUBE 10µF R4 22kΩ LOAD CC BATT- TLO GND C2 0.01µF RSENSE SEE FIGURE 19 FOR SWITCH-MODE CHARGER CIRCUIT. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX712/MAX713 General Description MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers ABSOLUTE MAXIMUM RATINGS V+ to BATT- .................................................................-0.3V, +7V BATT- to GND ........................................................................±1V BATT+ to BATTPower Not Applied............................................................±20V With Power Applied ................................The higher of ±20V or ±2V x (programmed cells) DRV to GND ..............................................................-0.3V, +20V FASTCHG to BATT- ...................................................-0.3V, +12V All Other Pins to GND......................................-0.3V, (V+ + 0.3V) V+ Current.........................................................................100mA DRV Current. .....................................................................100mA REF Current.........................................................................10mA Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 10.53mW/°C above +70°C............842mW Narrow SO (derate 8.70mW/°C above +70°C .............696mW CERDIP (derate 10.00mW/°C above +70°C ................800mW Operating Temperature Ranges MAX71_C_E .......................................................0°C to +70°C MAX71_E_E .................................................... -40°C to +85°C MAX71_MJE ................................................. -55°C to +125°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (IV+ = 10mA, TA = TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect to BATT-, not GND.) PARAMETER V+ Voltage CONDITIONS 5mA < IV+ < 20mA IV+ (Note 1) MIN TYP 4.5 MAX 5.5 5 BATT+ Leakage V+ = 0V, BATT+ = 17V BATT+ Resistance with Power On PGM0 = PGM1 = BATT-, BATT+ = 30V C1 Capacitance C2 Capacitance UNITS V mA 5 µA 30 kΩ 0.5 µF 5 nF REF Voltage 0mA < IREF < 1mA 1.96 2.04 V Undervoltage Lockout Per cell 0.35 0.50 V External VLIMIT Input Range 1.25 2.50 V THI, TLO, TEMP Input Range 0 2 V -10 10 mV THI, TLO Offset Voltage (Note 2) 0V < TEMP < 2V, TEMP voltage rising THI, TLO, TEMP, VLIMIT Input Bias Current -1 1 µA VLIMIT Accuracy 1.2V < VLIMIT < 2.5V, 5mA < IDRV < 20mA, PGM0 = PGM1 = V+ -30 30 mV Internal Cell Voltage Limit VLIMIT = V+ 1.6 1.65 1.7 V mV Fast-Charge VSENSE Trickle-Charge VSENSE Voltage-Slope Sensitivity (Note 3) 225 250 275 PGM3 = V+ 1.5 3.9 7.0 PGM3 = open 4.5 7.8 12.0 PGM3 = REF 12.0 15.6 20.0 PGM3 = BATT- 26.0 31.3 38.0 MAX713 -2.5 MAX712 0 mV mV/tA per cell Timer Accuracy -15 15 % Battery-Voltage to Cell-Voltage Divider Accuracy -1.5 1.5 % DRV Sink Current 2 VDRV = 10V 30 _______________________________________________________________________________________ mA NiCd/NiMH Battery Fast-Charge Controllers (IV+ = 10mA, TA = TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect to BATT-, not GND.) PARAMETER CONDITIONS MIN FASTCHG Low Current V FASTCHG = 0.4V FASTCHG High Current V FASTCHG = 10V A/D Input Range (Note 4) Battery voltage ÷ number of cells programmed TYP MAX UNITS 2 mA 1.4 10 µA 1.9 V Note 1: The MAX712/MAX713 are powered from the V+ pin. Since V+ shunt regulates to +5V, R1 must be small enough to allow at least 5mA of current into the V+ pin. Note 2: Offset voltage of THI and TLO comparators referred to TEMP. Note 3: tA is the A/D sampling interval (Table 3). Note 4: This specification can be violated when attempting to charge more or fewer cells than the number programmed. To ensure proper voltage-slope fast-charge termination, the (maximum battery voltage) ÷ (number of cells programmed) must fall within the A/D input range. Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) CURRENT-SENSE AMPLIFIER FREQUENCY RESPONSE (with 15pF) CURRENT-SENSE AMPLIFIER FREQUENCY RESPONSE (with 10nF) MAX712/13 toc01 40 MAX712/13 toc02 20 C2 = 15pF FASTCHG = 0V 0 + VIN - CC + CURRENTSENSE AMP GND -40 Φ -80 -10 -120 -20 -80 VOUT - BATT- -20 1k 0 100k 10k 1M 10M -120 10 FREQUENCY (Hz) SHUNT-REGULATOR VOLTAGE vs. CURRENT 5.4 1 5.2 5.0 DRV SINKING CURRENT 4.8 4.6 MAX712/13 toc05 1.6 TEMP PIN VOLTAGE (V) 10 DRV NOT SINKING CURRENT 5.6 ALPHA SENSORS PART No. 14A1002 STEINHART-HART INTERPOLATION MAX712/13 toc04 MAX712/13 toc03 5.8 V+ VOLTAGE (V) DRV PIN SINK CURRENT(mA) FASTCHG = 0V, V+ = 5V 10k FREQUENCY (Hz) CURRENT ERROR-AMPLIFIER TRANSCONDUCTANCE 100 1k 100 35 1.4 30 1.2 25 1.0 20 0.8 15 0.6 10 0.4 5 4.4 4.2 0.1 1.95 4.0 1.97 1.99 2.01 VOLTAGE ON CC PIN (V) 2.03 2.05 0.2 0 10 20 30 40 CURRENT INTO V+ PIN (mA) 50 60 BATTERY THERMISTOR RESISTANCE (kΩ) BATT- -10 -40 AV GAIN (dB) Φ 0 10 AV PHASE (DEGREES) GAIN (dB) 10 0 40 C2 = 10nF FASTCHG = 0V PHASE (DEGREES) 20 0 0 10 20 30 40 50 60 BATTERY TEMPERATURE(°C) _______________________________________________________________________________________ 3 MAX712/MAX713 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX713 NiCd BATTERY CHARGING CHARACTERISTICS AT C RATE MAX713 NiMH BATTERY CHARGING CHARACTERISTICS AT C RATE MAX712/13 toc06 30 25 1.40 30 60 30 1.50 T 25 1.45 90 0 30 60 CHARGE TIME (MINUTES) MAX713 NiCd BATTERY-CHARGING CHARACTERISTICS AT C/2 RATE MAX713 NiMH BATTERY CHARGING CHARACTERISTICS AT C/2 RATE MAX712/13 toc09 30 V T 25 1.40 0 50 100 CELL VOLTAGE (V) 1.45 35 CELL TEMPERATURE (°C) CELL VOLTAGE (V) 1.55 ∆V CUTOFF ∆t 1.50 1.50 35 V 1.45 30 T 1.40 0 150 MAX712/13 toc10 1.60 40 35 30 T 25 5 10 15 20 CELL VOLTAGE (V) 1.55 1.45 4 MAX712/13 toc11 V 1.60 CELL TEMPERATURE (°C) ∆V CUTOFF ∆t CHARGE TIME (MINUTES) 100 50 150 CHARGE TIME (MINUTES) 1.65 5 MINUTE REST BETWEEN CHARGES V 25 MAX713 CHARGING CHARACTERISTICS OF A FULLY CHARGED NiMH BATTERY MAX713 CHARGING CHARACTERISTICS OF A FULLY-CHARGED NiMH BATTERY 1.65 40 ∆V CUTOFF ∆t CHARGE TIME (MINUTES) 0 90 CHARGE TIME (MINUTES) MAX712/13 toc08 1.50 35 40 ∆V CUTOFF ∆t 1.55 35 5-HOUR REST BETWEEN CHARGES 1.50 30 T 25 1.45 0 5 10 15 CHARGE TIME (MINUTES) 20 _______________________________________________________________________________________ CELL TEMPERATURE (°C) 0 ∆V CUTOFF ∆t V CELL TEMPERATURE (°C) T 1.45 1.55 CELL TEMPERATURE (°C) 35 40 1.60 CELL VOLTAGE (V) ∆V CUTOFF ∆t V 1.50 CELL TEMPERATURE (°C) CELL VOLTAGE (V) MAX712/13 toc07 40 1.55 CELL VOLTAGE (V) MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers NiCd/NiMH Battery Fast-Charge Controllers PIN NAME FUNCTION 1 VLIMIT Sets the maximum cell voltage. The battery terminal voltage (BATT+ - BATT-) will not exceed VLIMIT x (number of cells). Do not allow VLIMIT to exceed 2.5V. Tie VLIMIT to VREF for normal operation. 2 BATT+ Positive terminal of battery 3, 4 PGM0, PGM1 PGM0 and PGM1 set the number of series cells to be charged. The number of cells can be set from 1 to 16 by connecting PGM0 and PGM1 to any of V+, REF, or BATT-, or by leaving the pin open (Table 2). For cell counts greater than 11, see the Linear-Mode, High Series Cell Count section. Charging more or fewer cells than the number programmed may inhibit ∆V fast-charge termination. 5 THI Trip point for the over-temperature comparator. If the voltage-on TEMP rises above THI, fast charge ends. 6 TLO Trip point for the under-temperature comparator. If the MAX712/MAX713 power on with the voltage-on TEMP less than TLO, fast charge is inhibited and will not start until TEMP rises above TLO. 7 TEMP 8 FASTCHG Open-drain, fast-charge status output. While the MAX712/MAX713 fast charge the battery, FASTCHG sinks current. When charge ends and trickle charge begins, FASTCHG stops sinking current. 9, 10 PGM2, PGM3 PGM2 and PGM3 set the maximum time allowed for fast charging. Timeouts from 33 minutes to 264 minutes can be set by connecting to any of V+, REF, or BATT-, or by leaving the pin open (Table 3). PGM3 also sets the fast-charge to trickle-charge current ratio (Table 5). 11 CC 12 BATT- Negative terminal of battery 13 GND System ground. The resistor placed between BATT- and GND monitors the current into the battery. 14 DRV Current sink for driving the external PNP current source 15 V+ Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt current powers the MAX712/MAX713. 16 REF 2V reference output Sense input for temperature-dependent voltage from thermistors. Compensation input for constant current regulation loop _______________________________________________________________________________________ 5 MAX712/MAX713 Pin Description MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers Getting Started The MAX712/MAX713 are simple to use. A complete linear-mode or switch-mode fast-charge circuit can be designed in a few easy steps. A linear-mode design uses the fewest components and supplies a load while charging, while a switch-mode design may be necessary if lower heat dissipation is desired. 1) Follow the battery manufacturer’s recommendations on maximum charge currents and charge-termination methods for the specific batteries in your application. Table 1 provides general guidelines. Table 1. Fast-Charge Termination Methods Charge Rate NiMH Batteries NiCd Batteries > 2C ∆V/∆t and temperature, MAX712 or MAX713 ∆V/∆t and/or temperature, MAX713 2C to C/2 ∆V/∆t and/or temperature, MAX712 or MAX713 ∆V/∆t and/or temperature, MAX713 < C/2 ∆V/∆t and/or temperature, MAX712 ∆V/∆t and/or temperature, MAX713 2) Decide on a charge rate (Tables 3 and 5). The slowest fast-charge rate for the MAX712/MAX713 is C/4, because the maximum fast-charge timeout period is 264 minutes. A C/3 rate charges the battery in about three hours. The current in mA required to charge at this rate is calculated as follows: IFAST = (capacity of battery in mAh) ––––––––––––––––––––––––– (charge time in hours) Depending on the battery, charging efficiency can be as low as 80%, so a C/3 fast charge could take 3 hours and 45 minutes. This reflects the efficiency with which electrical energy is converted to chemical energy within the battery, and is not the same as the powerconversion efficiency of the MAX712/MAX713. 3) Decide on the number of cells to be charged (Table 2). If your battery stack exceeds 11 cells, see the LinearMode High Series Cell Count section. Whenever changing the number of cells to be charged, PGM0 6 and PGM1 must be adjusted accordingly. Attempting to charge more or fewer cells than the number programmed can disable the voltage-slope fast-charge termination circuitry. The internal ADC’s input voltage range is limited to between 1.4V and 1.9V (see the Electrical Characteristics), and is equal to the voltage across the battery divided by the number of cells programmed (using PGM0 and PGM1, as in Table 2). When the ADC’s input voltage falls out of its specified range, the voltage-slope termination circuitry can be disabled. 4) Choose an external DC power source (e.g., wall cube). Its minimum output voltage (including ripple) must be greater than 6V and at least 1.5V higher (2V for switch mode) than the maximum battery voltage while charging. This specification is critical because normal fast-charge termination is ensured only if this requirement is maintained (see Powering the MAX712/MAX713 section for more details). 5) For linear-mode designs, calculate the worst-case power dissipation of the power PNP and diode (Q1 and D1 in the Typical Operating Circuit) in watts, using the following formula: PD PNP = (maximum wall-cube voltage under load - minimum battery voltage) x (charge current in amps) If the maximum power dissipation is not tolerable for your application, refer to the Detailed Description or use a switch-mode design (see Switch-Mode Operation in the Applications Information section, and see the MAX713 EV kit manual). 6) For both linear and switch-mode designs, limit current into V+ to between 5mA and 20mA. For a fixed or narrow-range input voltage, choose R1 in the Typical Operation Circuit using the following formula: R1 = (minimum wall-cube voltage - 5V) / 5mA For designs requiring a large input voltage variation, choose the current-limiting diode D4 in Figure 19. 7) Choose RSENSE using the following formula: RSENSE = 0.25V / (IFAST) 8) Consult Tables 2 and 3 to set pin-straps before applying power. For example, to fast charge at a rate of C/2, set the timeout to between 1.5x or 2x the charge period, three or four hours, respectively. _______________________________________________________________________________________ NiCd/NiMH Battery Fast-Charge Controllers NUMBER OF CELLS Table 3. Programming the Maximum Charge Time PGM1 CONNECTION PGM0 CONNECTION 1 V+ V+ 2 Open V+ 3 REF V+ 4 BATT- 5 TIMEOUT (min) A/D SAMPLING INTERVAL (s) (tA) VOLTAGESLOPE TERMINATION PGM3 CONN PGM2 CONN 22 21 Disabled V+ Open 22 21 Enabled V+ REF V+ 33 21 Disabled V+ V+ V+ Open 33 21 Enabled V+ BATT- 6 Open Open 45 42 Disabled Open Open 7 REF Open 45 42 Enabled Open REF 8 BATT- Open 66 42 Disabled Open V+ 9 V+ REF 66 42 Enabled Open BATT- 10 Open REF 90 84 Disabled REF Open 11 REF REF 90 84 Enabled REF REF REF 132 84 Disabled REF V+ 132 84 Enabled REF BATT- 180 168 Disabled BATT- Open 180 168 Enabled BATT- REF 264 168 Disabled BATT- V+ 264 168 Enabled BATT- BATT- 12 BATT- MAX712/MAX713 Table 2. Programming the Number of Cells 13 V+ BATT- 14 Open BATT- 15 REF BATT- 16 BATT- BATT- V+ +5V SHUNT REGULATOR PGM2 GND PGM3 FASTCHG TIMED_OUT BATT- N POWER_ON_RESET TIMER BATTFAST_CHARGE PGM2 PGM3 THI TEMP TLO ∆V DETECTION ∆V_DETECT CONTROL LOGIC IN_REGULATION DRV CC V+ BATT100kΩ GND VLIMIT BATT+ UNDER_VOLTAGE HOT TEMPERATURE COMPARATORS CURRENT AND VOLTAGE REGULATOR PGMx 100kΩ COLD PGM0 CELL_VOLTAGE MAX712 MAX713 0.4V BATT- REF PGM1 BATT- INTERNAL IMPEDANCE OF PGM0–PGM3 PINS Figure 1. Block Diagram _______________________________________________________________________________________ 7 Detailed Description CURRENT INTO CELL 1.5 1.4 CELL TEMPERATURE CELL VOLTAGE (V) The MAX712/MAX713 fast charge NiMH or NiCd batteries by forcing a constant current into the battery. The MAX712/MAX713 are always in one of two states: fast charge or trickle charge. During fast charge, the current level is high; once full charge is detected, the current reduces to trickle charge. The device monitors three variables to determine when the battery reaches full charge: voltage slope, battery temperature, and charge time. VOLTAGE 1.3 TEMPERATURE 0.4 0 A mA µA 1 2 1. NO POWER TO CHARGER 2. CELL VOLTAGE LESS THAN 0.4V 3. FAST CHARGE 4. TRICKLE CHARGE 5. CHARGER POWER REMOVED 3 4 5 TIME When the cell voltage slope becomes negative, fast charge is terminated and the MAX712/MAX713 revert to trickle-charge state (time 4). When power is removed (time 5), the device draws negligible current from the battery. Figure 3 shows a typical charging event using temperature full-charge detection. In the case shown, the battery pack is too cold for fast charging (for instance, brought in from a cold outside environment). During time 2, the MAX712/MAX713 remain in trickle-charge state. Once a safe temperature is reached (time 3), fast charge starts. When the battery temperature exceeds the limit set by THI, the MAX712/MAX713 revert to trickle charge (time 4). CELL VOLTAGE (V) VREF = VLIMIT THI TLO A mA µA 1 2 1. NO POWER TO CHARGER 2. CELL TEMPERATURE TOO LOW 3. FAST CHARGE 4. TRICKLE CHARGE 3 TIME Figure 3. Typical Charging Using Temperature 8 Figure 1 shows the block diagram for the MAX712/ MAX713. The timer, voltage-slope detection, and temperature comparators are used to determine full charge state. The voltage and current regulator controls output voltage and current, and senses battery presence. Figure 2 shows a typical charging scenario with batteries already inserted before power is applied. At time 1, the MAX712/MAX713 draw negligible power from the battery. When power is applied to DC IN (time 2), the power-on reset circuit (see the POWER_ON_RESET signal in Figure 1) holds- the- MAX712/MAX713 in trickle charge. Once POWER_ON_RESET goes high, the device enters the fast-charge state (time 3) as long as the cell voltage is above the undervoltage lockout (UVLO) voltage (0.4V per cell). Fast charging cannot start until (battery voltage) / (number of cells) exceeds 0.4V. CURRENT INTO CELL CELL TEMPERATURE Figure 2. Typical Charging Using Voltage Slope CURRENT INTO CELL MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers 4 1.5 1.4 1.3 A mA µA 1 1. BATTERY NOT INSERTED 2. FAST CHARGE 3. TRICKLE CHARGE 4. BATTERY REMOVED 2 3 TIME Figure 4. Typical Charging with Battery Insertion _______________________________________________________________________________________ 4 NiCd/NiMH Battery Fast-Charge Controllers the voltage on the battery pack is higher during a fastcharge cycle than while in trickle charge or while supplying a load. The voltage across some battery packs may approach 1.9V/cell. Q1 R2 R1 2N3904 Powering the MAX712/MAX713 AC-to-DC wall-cube adapters typically consist of a transformer, a full-wave bridge rectifier, and a capacitor. Figures 10–12 show the characteristics of three consumer product wall cubes. All three exhibit substantial 120Hz output voltage ripple. When choosing an adapter for use with the MAX712/MAX713, make sure the lowest wall-cube voltage level during fast charge and full load is at least 1.5V higher (2V for switch mode) than the maximum battery voltage while being fast charged. Typically, D1 DC IN V+ DRV MAX712 MAX713 Figure 5. DRV Pin Cascode Connection (for high DC IN voltage or to reduce MAX712/MAX713 power dissipation in linear mode) Table 4. MAX712/MAX713 Charge-State Transition Table† POWER_ON_RESET UNDER_VOLTAGE IN_REGULATION COLD HOT 0 x x x x Set trickle ↑ 1 x x x No change ↑ x 1 x x No change ↑ x x 0 x No change ↑ x x x 0 No change*** ↑ 0 0 1 1 Set fast 1 0 0 1 1 No change 1 0 0 ↓ 1 No change 1 ↓ 0 1 1 Set fast 1 0 ↓ 1 1 Set fast 1 0 0 1 ↑ No change*** 1 0 0 ↑ 1 Set fast** 1 x x 0 x Trickle to fast transition inhibited 1 x x x 0 Trickle to fast transition inhibited 1 ↑ 0 x x Set trickle 1 0 ↑ x x Set trickle 1 x x x ↓ Set trickle RESULT* † Only two states exist: fast charge and trickle charge. * Regardless of the status of the other logic lines, a timeout or a voltage-slope detection will set trickle charge. ** If the battery is cold at power-up, the first rising edge on COLD will trigger fast charge; however, a second rising edge will have no effect. *** Batteries that are too hot when inserted (or when circuit is powered up) will not enter fast charge until they cool and power is recycled. _______________________________________________________________________________________ 9 MAX712/MAX713 The MAX712/MAX713 can be configured so that voltage slope and/or battery temperature detects full charge. Figure 4 shows a charging event in which a battery is inserted into an already powered-up MAX712/MAX713. During time 1, the charger’s output voltage is regulated at the number of cells times VLIMIT. Upon insertion of the battery (time 2), the MAX712/MAX713 detect current flow into the battery and switch to fast-charge state. Once full charge is detected, the device reverts to trickle charge (time 3). If the battery is removed (time 4), the MAX712/MAX713 remain in trickle charge and the output voltage is once again regulated as in time 1. MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers shunt regulator sinks current to regulate V+ to 5V, and fast charge commences. The MAX712/MAX713 fast charge until one of the three fast-charge terminating conditions is triggered. If DC IN exceeds 20V, add a cascode connection in series with the DRV pin as shown in Figure 5 to prevent exceeding DRV’s absolute maximum ratings. Furthermore, if Figure 19’s DC IN exceeds 15V, a transistor level-shifter is needed to provide the proper voltage swing to the MOSFET gate. See the MAX713 EV kit manual for details. DC IN V+ REF DRV VLIMIT D1 CELL_VOLTAGE Select the current-limiting component (R1 or D4) to pass at least 5mA at the minimum DC IN voltage (see step 6 in the Getting Started section). The maximum current into V+ determines power dissipation in the MAX712/MAX713. maximum current into V+ = GND CURRENT-SENSE AMPLIFIER PGM3 FAST_CHARGE Av BATT- RSENSE GND X V+ OPEN REF BATT- 1 0 0 0 0 8 512 256 128 64 (maximum DC IN voltage - 5V) / R1 CC C2 BATT- BATTIN_REGULATION Fast Charge 1.25V BATT- Figure 6. Current and Voltage Regulator (linear mode) The 1.5V of overhead is needed to allow for worst-case voltage drops across the pass transistor (Q1 of Typical Operating Circuit), the diode (D1), and the sense resistor (RSENSE). This minimum input voltage requirement is critical, because violating it can inhibit proper termination of the fast-charge cycle. A safe rule of thumb is to choose a source that has a minimum input voltage = 1.5V + (1.9V x the maximum number of cells to be charged). When the input voltage at DC IN drops below the 1.5V + (1.9V x number of cells), the part oscillates between fast charge and trickle charge and might never completely terminate fast-charge. The MAX712/MAX713 are inactive without the wall cube attached, drawing 5µA (max) from the battery. Diode D1 prevents current conduction into the DRV pin. When the wall cube is connected, it charges C1 through R1 (see Typical Operating Circuit) or the current-limiting diode (Figure 19). Once C1 charges to 5V, the internal 10 power dissipation due to shunt regulator = 5V x (maximum current into V+) Sink current into the DRV pin also causes power dissipation. Do not allow the total power dissipation to exceed the specifications shown in the Absolute Maximum Ratings. The MAX712/MAX713 enter the fast-charge state under one of the following conditions: 1) Upon application of power (batteries already installed), with battery current detection (i.e., GND voltage is less than BATT- voltage), and TEMP higher than TLO and less than THI and cell voltage higher than the UVLO voltage. 2) Upon insertion of a battery, with TEMP higher than TLO and lower than THI and cell voltage higher than the UVLO voltage. RSENSE sets the fast-charge current into the battery. In fast charge, the voltage difference between the BATTand GND pins is regulated to 250mV. DRV current increases its sink current if this voltage difference falls below 250mV, and decreases its sink current if the voltage difference exceeds 250mV. fast-charge current (IFAST) = 0.25V / RSENSE Trickle Charge Selecting a fast-charge current (IFAST) of C/2, C, 2C, or 4C ensures a C/16 trickle-charge current. Other fastcharge rates can be used, but the trickle-charge current will not be exactly C/16. ______________________________________________________________________________________ NiCd/NiMH Battery Fast-Charge Controllers PGM3 FAST-CHARGE RATE TRICKLE-CHARGE CURRENT (ITRICKLE) V+ 4C IFAST/64 OPEN 2C IFAST/32 REF C IFAST/16 BATT- C/2 Q1 V+ Nonstandard Trickle-Charge Current Example Configuration: Typical Operating Circuit 2 x Panasonic P-50AA 500mAh AA NiCd batteries C/3 fast-charge rate 264-minute timeout Negative voltage-slope cutoff enabled Minimum DC IN voltage of 6V R7 DRV 10k MAX712 MAX713 BATTERY Q2 FASTCHG 10k IFAST/8 The MAX712/MAX713 internally set the trickle-charge current by increasing the current amplifier gain (Figure 6), which adjusts the voltage across R SENSE (see Trickle-Charge VSENSE in the Electrical Characteristics table). D1 DC IN RSENSE GND Figure 7. Reduction of Trickle Current for NiMH Batteries (Linear Mode) Regulation Loop The regulation loop controls the output voltage between the BATT+ and BATT- terminals and the current through the battery via the voltage between BATT- and GND. The sink current from DRV is reduced when the output voltage exceeds the number of cells times VLIMIT, or when the battery current exceeds the programmed charging current. Settings: Use MAX713 PGM0 = V+, PGM1 = open, PGM2 = BATT-, PGM3 = BATT-, RSENSE = 1.5Ω (fast-charge current, IFAST = 167mA), R1 = (6V - 5V) / 5mA = 200Ω Since PGM3 = BATT-, the voltage on RSENSE is regulated to 31.3mV during trickle charge, and the current is 20.7mA. Thus the trickle current is actually C/25, not C/16. For a linear-mode circuit, this loop provides the following functions: Further Reduction of Trickle-Charge Current for NiMH Batteries The voltage loop sets the maximum output voltage between BATT+ and BATT-. If VLIMIT is set to less than 2.5V, then: Maximum BATT+ voltage (referred to BATT-) = VLIMIT x (number of cells as determined by PGM0, PGM1) VLIMIT should be set between 1.9V and 2.5V. If VLIMIT is set below the maximum cell voltage, proper termination of the fast-charge cycle might not occur. Cell voltage can approach 1.9V/cell, under fast charge, in some battery packs. Tie VLIMIT to VREF for normal operation . With the battery removed, the MAX712/MAX713 do not provide constant current; they regulate BATT+ to the maximum voltage as determined above. The trickle-charge current can be reduced to less than C/16 using the circuit in Figure 7. In trickle charge, some of the current will be shunted around the battery, since Q2 is turned on. Select the value of R7 as follows: R7 = (VBATT + 0.4V) / (lTRlCKLE - IBATT) where V BATT = battery voltage when charged ITRlCKLE = MAX712/MAX713 trickle-charge current setting IBATT = desired battery trickle-charge current 1) When the charger is powered, the battery can be removed without interrupting power to the load. 2) If the load is connected as shown in the Typical Operating Circuit, the battery current is regulated regardless of the load current (provided the input power source can supply both). Voltage Loop ______________________________________________________________________________________ 11 MAX712/MAX713 Table 5. Trickle-Charge Current Determination from PGM3 The voltage loop is stabilized by the output filter capacitor. A large filter capacitor is required only if the load is going to be supplied by the MAX712/MAX713 in the absence of a battery. In this case, set COUT as: COUT (in farads) = (50 x ILOAD) / (VOUT x BWVRL) where BWVRL = loop bandwidth in Hz (10,000 recommended) COUT > 10µF ILOAD = external load current in amps VOUT = programmed output voltage (VLIMIT x number of cells) Current Loop Figure 6 shows the current-regulation loop for a linearmode circuit. To ensure loop stability, make sure that the bandwidth of the current regulation loop (BWCRL) is lower than the pole frequency of transistor Q1 (fB). Set BWCRL by selecting C2. BWCRL in Hz = gm / C2, C2 in farads, gm = 0.0018 Siemens The pole frequency of the PNP pass transistor, Q1, can be determined by assuming a single-pole current gain response. Both fT and Bo should be specified on the data sheet for the particular transistor used for Q1. fB in Hz = fT / Bo, fT in Hz, Bo = DC current gain Condition for Stability of Current-Regulation Loop: BWCRL < fB The MAX712/MAX713 dissipate power due to the current-voltage product at DRV. Do not allow the power dissipation to exceed the specifications shown in the Absolute Maximum Ratings. DRV power dissipation can be reduced by using the cascode connection shown in Figure 5 or by using a switch-mode circuit. Power dissipation due to DRV sink current = (current into DRV) x (voltage on DRV) Voltage-Slope Cutoff The MAX712/MAX713’s internal analog-to-digital converter has 2.5mV of resolution. It determines if the battery voltage is rising, falling, or unchanging by comparing the battery’s voltage at two different times. After power-up, a time interval of tA ranging from 21sec to 168sec passes (see Table 3 and Figure 8), then a battery voltage measurement is taken. It takes 5ms to perform a measurement. After the first measurement is complete, another t A interval passes, and then a second measurement is taken. The two measurements are compared, and a decision whether to terminate charge is made. If charge is not terminated, another full two-measurement cycle is repeated until charge is 12 terminated. Note that each cycle has two tA intervals and two voltage measurements. The MAX712 terminates fast charge when a comparison shows that the battery voltage is unchanging. The MAX713 terminates when a conversion shows the battery voltage has fallen by at least 2.5mV per cell. This is the only difference between the MAX712 and MAX713. Temperature Charge Cutoff Figure 9a shows how the MAX712/MAX713 detect overand under-temperature battery conditions using negative temperature coefficient thermistors. Use the same model thermistor for T1 and T2 so that both have the same nominal resistance. The voltage at TEMP is 1V (referred to BATT-) when the battery is at ambient temperature. The threshold chosen for THI sets the point at which fast charging terminates. As soon as the voltage-on TEMP rises above THI, fast charge ends, and does not restart after TEMP falls below THI. The threshold chosen for TLO determines the temperature below which fast charging will be inhibited. If TLO > TEMP when the MAX712/MAX713 start up, fast charge will not start until TLO goes below TEMP. The cold temperature charge inhibition can be disabled by removing R5, T3, and the 0.022µF capacitor; and by tying TLO to BATT-. To disable the entire temperature comparator chargecutoff mechanism, remove T1, T2, T3, R3, R4, and R5, and their associated capacitors, and connect THI to V+ and TLO to BATT-. Also, place a 68kQ resistor from REF to TEMP, and a 22kΩ resistor from BATT- to TEMP. Some battery packs come with a temperature-detecting thermistor connected to the battery pack’s negative COUNTS MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers VOLTAGE RISES NEGATIVE ZERO VOLTAGE VOLTAGE SLOPE SLOPE CUTOFF FOR MAX712 CUTOFF FOR MAX712 OR MAX713 ZERO RESIDUAL NEGATIVE RESIDUAL 0 POSITIVE RESIDUAL 5 5 5 5 5 5 tA ms tA ms tA ms tA ms tA ms tA ms INTERVAL INTERVAL INTERVAL INTERVAL INTERVAL INTERVAL NOTE: SLOPE PROPORTIONAL TO VBATT Figure 8. Voltage Slope Detection ______________________________________________________________________________________ t NiCd/NiMH Battery Fast-Charge Controllers REF R3 THI T1 HOT R4 0.022µF TEMP +2.0V Switch-Mode Operation R5 COLD T2 TLO MAX712 MAX713 T3 0.022µF 1µF BATTAMBIENT TEMPERATURE NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE REPLACED BY STANDARD RESISTORS. For applications where the power dissipation in the pass transistor cannot be tolerated (ie., where heat sinking is not feasible or is too costly), a switch-mode charger is recommended. Switch-mode operation can be implemented simply by using the circuit of Figure 19. The circuit of Figure 19 uses the error amplifier at the CC pin as a comparator with the 33pF capacitor adding hysteresis. Figure 19 is shown configured to charge two cells at 1A. Lower charge currents and a different number of cells can be accommodated simply by changing R SENSE and PGM0–PGM3 connections (Tables 2 and 3). The input power-supply voltage range is 8V to 15V and must be at least 2V greater than the peak battery voltage, under fast charge. As shown in Figure 19, the source should be capable of greater than 1.3A of output current. The source requirements are critical because if violated, proper termination of the fastcharge cycle might not occur. For input voltages greater than 15V, see the MAX713SWEVKIT data sheet. Figure 9a. Temperature Comparators REF __________Applications Information AMBIENT TEMPERATURE AMBIENT TEMPERATURE T2 THI R5 R3 10 TEMP 1µF COLD TLO 0.022µF 0.022µF MAX712 MAX713 T1 R4 T3 OUTPUT VOLTAGE (V) +2.0V MAX712/713 11 HOT HIGH PEAK 9 120Hz RIPPLE 8 LOW PEAK 7 BATTIN THERMAL CONTACT WITH BATTERY AMBIENT TEMPERATURE NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BE REPLACED BY STANDARD RESISTORS. Figure 9b. Alternative Temperature Comparator Configuration 6 0 200 400 600 800 1000 LOAD CURRENT (mA) Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic, 9VDC 800mA ______________________________________________________________________________________ 13 MAX712/MAX713 terminal. In this case, use the configuration shown in Figure 9b. Thermistors T2 and T3 can be replaced by standard resistors if absolute temperature charge cutoff is acceptable. All resistance values in Figures 9a and 9b should be chosen in the 10kΩ to 500kΩ range. IN THERMAL CONTACT WITH BATTERY The voltage-slope, fast-charge termination circuitry might become disabled if attempting to charge a different number of cells than the number programmed. The switching frequency (nominally 30kHz) can be decreased by increasing the value of the capacitor connected between CC and BATT-. Make sure that the two capacitors connected to the CC node are placed as close as possible to the CC pin on the MAX712/MAX713 and that their leads are of minimum length. The CC node is a high-impedance point, so do not route logic lines near the CC pin. The circuit of Figure 19 cannot service a load while charging. Order the MAX713SWEVKIT-SO for quick evaluation of the MAX712/MAX713 in switch-mode operation. For more information on switch-mode operation and ordering information for external components, order the MAX713EVKIT data sheet. 10 DC IN = Sony AC-190 +9VDC at 800mA AC-DC adapter PGM0 = V+, PGM1 = REF, PGM2 = REF, PGM3 = REF R1 = 200Ω, R2 = 150Ω, RSENSE = 0.25Ω C1 = 1µF, C2 = 0.01µF, C3 = 10µF, VLIMIT = REF R3 = 10kΩ, R4 = 15kΩ T1, T2 = part #14A1002 (Alpha Sensors: 858-549-4660) R5 omitted, T3 omitted, TLO = BATT- 16 HIGH PEAK 9 8 120Hz RIPPLE 7 LOW PEAK 14 HIGH PEAK 12 LOW PEAK 10 6 120Hz RIPPLE 8 5 400 800 600 LOAD CURRENT (mA) 0 1000 Figure 11. Sony CD Player AC Adapter AC-96N Load Characteristic, 9VDC 600mA ∆V CUTOFF ∆t 4.9 4.8 5.0 38 4.9 36 4.7 34 V 4.6 32 4.5 30 T 4.4 4.2 0 60 30 TIME (MINUTES) Figure 13. 3 NiMH Cells Charged with MAX712 90 MAX712/713 ∆V CUTOFF ∆t 40 38 4.8 36 34 4.7 V 4.6 32 30 4.5 T 4.4 28 26 4.3 26 24 4.2 28 4.3 800 Figure 12. Panasonic Modem AC Adapter KX-A11 Load Characteristic, 12VDC 500mA 40 BATTERY TEMPERATURE (°C) MAX712/713 5.0 200 600 400 LOAD CURRENT (mA) 24 0 60 30 TIME (MINUTES) Figure 14. NiMH Cells Charged with MAX713 ______________________________________________________________________________________ 90 BATTERY TEMPERATURE (°C) 200 BATTERY VOLTAGE (V) 0 14 MAX712/713 18 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) Battery-Charging Examples Figures 13 and 14 show the results of charging 3 AA, 1000mAh, NiMH batteries from Gold Peak (part no. GP1000AAH, GP Batteries (619) 438-2202) at a 1A rate using the MAX712 and MAX713, respectively. The Typical Operating Circuit is used with Figure 9a’s thermistor configuration . MAX712/713 11 BATTERY VOLTAGE (V) MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers NiCd/NiMH Battery Fast-Charge Controllers Efficiency During Discharge The current-sense resistor, R SENSE, causes a small efficiency loss during battery use. The efficiency loss is Q1 significant only if R SENSE is much greater than the battery stack’s internal resistance. The circuit in Figure 16 can be used to shunt the sense resistor whenever power is removed from the charger. Status Outputs Figure 17 shows a circuit that can be used to indicate charger status with logic levels. Figure 18 shows a circuit that can be used to drive LEDs for power and charger status. D1 DC IN TO BATTERY POSITIVE TERMINAL R2 150Ω OV = NO POWER 5V = POWER V+ 33kΩ Q2 VCC MAX712 MAX713 10kΩ 500Ω OV = FAST VCC = TRICKLE OR NO POWER FASTCHG DRV BATT+ MAX712 MAX713 Figure 15. Cascoding to Accommodate High Cell Counts for Linear-Mode Circuits Figure 17. Logic-Level Status Outputs DC IN D1 R1 >4 CELLS MAX712 MAX713 CHARGE POWER 100kΩ V+ * 100kΩ RSENSE V+ * LOW RON LOGIC LEVEL N-CHANNEL POWER MOSFET GND Figure 16. Shunting RSENSE for Efficiency Improvement 470ΩMIN MAX712 MAX713 FAST CHARGE FASTCHG Figure 18. LED Connection for Status Outputs ______________________________________________________________________________________ 15 MAX712/MAX713 Linear-Mode, High Series Cell Count The absolute maximum voltage rating for the BATT+ pin is higher when the MAX712/MAX713 are powered on. If more than 11 cells are used in the battery, the BATT+ input voltage must be limited by external circuitry when DC IN is not applied (Figure 15). MAX712/MAX713 NiCd/NiMH Battery Fast-Charge Controllers L1 D03340 M1 IRFR9024 DC IN 220µH 8V TO 15V R2 5.1kΩ C6 10µF 50V C5 10µF 50V 3 1 D4 CCLHM080 (8mA CURRENTLIMITING DIODE) 3 Q4 CMPTA06 Q1 CMPTA06 D1 MBRS340T3 D2 MBRS340T3 2 2 1 Q2 2N2907 1 3 2 14 5 15 3 THI 11 CC DRV C2 220pF V+ PGM0 MAX713 BATT+ 4 2 C3 10µF 50V PGM1 9 PGM2 10 REF 16 R6 68kΩ R7 22kΩ C1 1µF 10V 1 7 BATT- PGM3 TLD 12 6 REF GND VLIMIT TEMP C4 0.1µF 2 x 1000mA-Hr NiCd CELLS BATT– R3 0.25Ω 13 FASTCHG 8 R5 470Ω Figure 19. Simplest Switch-Mode Charger 16 BATT + ______________________________________________________________________________________ NiCd/NiMH Battery Fast-Charge Controllers PART TEMP RANGE ___________________Chip Topography PIN-PACKAGE MAX713CPE 0°C to +70°C 16 Plastic DIP MAX713CSE MAX713C/D MAX713EPE 0°C to +70°C 0°C to +70°C -40°C to +85°C 16 Narrow SO Dice* 16 Plastic DIP MAX713ESE MAX713MJE -40°C to +85°C -55°C to +125°C 16 Narrow SO 16 CERDIP** BATT+ VLIMIT REF V+ DRV PGM0 PGM1 *Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883. GND 0.126 (3.200mm) BATTTHI CC TLO PGM3 TEMP FASTCHG PGM2 0.80" (2.032mm) TRANSISTOR COUNT: 2193 SUBSTRATE CONNECTED TO V+ Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 17 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX712/MAX713 Ordering Information (continued)