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19-0371; Rev 4; 5/97
NUAL KIT MA ATION EET EVALU ATA SH WS D FOLLO
NiCd/NiMH Battery Fast-Charge Controllers
____________________________Features
o Stand-Alone NiCd or NiMH Fast Chargers o New Pulsed Trickle-Charge Mode (MAX2003A only) o Provide Switch-Mode, Gated, or Linear Control Regulation o Small, Narrow SO Package Available o On-Chip Fast-Charge Termination Methods: * Temperature Slope * Maximum Voltage * Negative Delta Voltage * Maximum Time * Maximum Temperature o Automatically Switch from Fast-Charge to Trickle-Charge or Top-Off Charge o Optional Discharge-Before-Charge o Directly Drive Status LEDs o Optional Top-Off Charge
General Description
The MAX2003/MAX2003A are fast-charge battery chargers (with conditioning) for NiCd (nickel cadmium) or NiMH (nickel-metal hydride) rechargeable batteries. The MAX2003A has the same features as the MAX2003 with an additional pulsed trickle-charge mode to prevent dendrite formation in NiMH batteries. Each can be configured as a switch-mode current regulator or as a gating controller for an external current source. Switch-mode current regulation provides efficient energy transfer, reducing power dissipation and the associated heating. Gating control of an external current source requires minimal components, saving space and cost. On-chip algorithms determine charge termination, so the MAX2003/MAX2003A can be used as stand-alone chargers. Fast-charge termination is accomplished by five methods: temperature slope, negative voltage change, maximum temperature, maximum time, and maximum voltage. As a safety feature, the start of fastcharge is inhibited until battery voltage and temperature are within safe limits. By selecting the appropriate charge-termination method, a single circuit can be built with the MAX2003/MAX2003A to fast-charge both NiMH and NiCd batteries. The MAX2003/MAX2003A provide a switch-activated discharge-before-charge option that allows for battery conditioning and more accurate capacity measurement. Other features include optional top-off charging and direct drivers for LED status lights. The MAX2003, in DIP and wide SO packages, is a direct plug-in replacement for the bq2003. The MAX2003/ MAX2003A also come in a space-saving narrow SO package. The MAX2003A evaluation kit (MAX2003A EVKIT-SO) is available to assist in designs.
MAX2003/MAX2003A
Ordering Information
PART MAX2003CPE MAX2003CSE MAX2003CWE MAX2003C/D MAX2003ACPE MAX2003ACSE MAX2003ACWE MAX2003AC/D TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 16 Plastic DIP 16 Narrow SO 16 Wide SO Dice* 16 Plastic DIP 16 Narrow SO 16 Wide SO Dice*
* Contact factory for dice specifications.
___________________Pin Configuration
TOP VIEW
CCMD 1 DCMD 2 DVEN 3 TM1 4 TM2 5 TS 6 BAT 7 VSS 8 16 VCC 15 DIS 14 MOD
________________________Applications
Battery-Powered Equipment: Laptop, Notebook, and Palmtop Computers Handy-Terminals Portable Consumer Products: Portable Stereos Cordless Phones Backup-Battery Applications: Memory Hold-Up Emergency Switchovers
MAX2003 MAX2003A
13 CHG 12 TEMP 11 MCV 10 TCO 9 SNS
DIP/SO
________________________________________________________________ Maxim Integrated Products
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NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
ABSOLUTE MAXIMUM RATINGS
All Pins to VSS ...........................................................-0.3V, +6.0V Continuous Power Dissipation (TA = +70C) Plastic DIP (derate 10.53mW/C above +70C) ...........842mW Narrow SO (derate 8.70mW/C above +70C) .............696mW Wide SO (derate 9.52mW/C above +70C).................762mW Operating Temperature Range...............................0C to +70C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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
(VCC = 4.5V to 5.5V, Figure 1, all measurements are with respect to VSS, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Supply Voltage Supply Current Cell Potential Battery Voltage Input Temperature Potential Temperature Sense Input Voltage End-of-Discharge Voltage Maximum Cell Voltage Low-Temperature Trip Threshold Temperature Cutoff Voltage High-Temperature Trip Threshold SYMBOL VCC ICC VCELL VBAT VTEMP VTS VEDV VMCV VLTF VTCO VHTF VCC = 5V VCC = 5V VCC = 5V VCC = 5V VCC = 5V, VTCO = 1.4V VTS - VSNS No load VBAT - VSNS 0.0 0.0 0.0 0.0 0.2VCC - 30mV VEDV 0.4VCC - 30mV VLTF - 0.2VCC (VLTF/8) + (7VTCO/8) - 30mV 0.05VCC - 25mV 0.044VCC - 25mV (VLTF/8) + 7VTCO/8 0.4VCC 0.2VCC CONDITIONS MIN 4.5 TYP 5.0 0.75 MAX 5.5 2.2 VCC VCC VCC VCC 0.2VCC + 30mV VEDV + 0.2VCC 0.4VCC + 30mV VLTF (VLTF/8) + (7VTCO/8) + 30mV 0.05VCC + 25mV 0.044VCC + 25mV UNITS V mA V V V V V V V V V
Sense Trip Threshold High Sense Trip Threshold Low Delta Sense Voltage (Note 1) Negative Delta Voltage (Note 2) Thermistor Input Resolution (Note 2)
VSNSHI VSNSLO VSNSHI VSNSLO -V VTHERM
VCC = 5V VCC = 5V
0.05VCC 0.044VCC 30
V V mV mV mV
VCC = 5V VCC = 5V
12 16
2
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NiCd/NiMH Battery Fast-Charge Controllers
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 4.5V to 5.5V, Figure 1, all measurements are with respect to VSS, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Logic-High Threshold SYMBOL VOH CONDITIONS For DIS, TEMP and CHG, 0mA ILOAD 5mA; For MOD, 0mA ILOAD 10mA For DIS, TEMP and CHG, 0mA ILOAD 5mA; For MOD, 0mA ILOAD 10mA CCMD, DCMD, DVEN TM1, TM2 CCMD, DCMD, DVEN TM1, TM2 CCMD, DCMD, DVEN at VCC and VSS TM1, TM2 = VCC TM1, TM2 = VSS TM1, TM2 = tri-state BAT, MCV, TCO, SNS, TS -2.0 50 -1.0 -70.0 70.0 2.0 VCC - 1.0 VCC - 0.3 1.0 0.3 1.0 MIN VCC - 0.5 TYP MAX UNITS V
MAX2003/MAX2003A
Logic-Low Threshold
VOL
0.5
V
Input Logic Voltage High Input Logic Voltage Low Input Logic Leakage Input Logic Current High Input Logic Current Low Input Logic Current High-Z Input Impedance
VIH VIL ILKG IIH IIL IIZ
V V A A A A M
Note 1: The sense trip levels are determined by an internal resistor divider network that provides a typical difference of 30mV from SNSHI to SNSLO. Slight variation in this delta is seen if there is a resistor mismatch in the network. Note 2: Typical variations of Negative Delta Voltage and Thermistor Input Resolution parameters are less than 4mV.
TIMING CHARACTERISTICS
(VCC = 4.5V to 5.5V, Figure 1, all measurements are with respect to VSS, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 5.0V, TA = +25C.) PARAMETER Minimum Pulse Width Variation of Fast-Charge Timeout MOD Switching Frequency Battery Replacement Timeout (Note 4) fMAX tBTO SYMBOL tMPW CCMD, DCMD (Note 3) MOD pin in fast-charge mode, VCC = 5V 200 250 CONDITIONS MIN 1.0 0.84 1.00 1.16 100 300 kHz ms TYP MAX UNITS s
Note 3: Ratio of actual versus expected timeout (see Table 4). Tested with TM1 = TM2 = floating. Note 4: To recognize a battery insert signal, VBAT must be greater than VMCV for at least tBTO.
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NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
______________________________________________________________Pin Description
PIN NAME CCMD DCMD DVEN TM1, TM2 TS FUNCTION Charge-Enabled Mode Input--initiates fast-charge on a digital signal (see Detailed Description for operating conditions). Discharge-Enable Mode Input--initiates discharge-before-charge on a digital signal (see Detailed Description for operating conditions). Negative Delta Voltage (-V) Enable Input--enables -V charge-termination mode. If DVEN is high, the controller uses negative-voltage change detection to terminate charge. If DVEN is low, this mode is disabled. These inputs are used to program the fast-charge and hold-off times, and to enable the top-off charge mode. The inputs can be high, low, or floating. See Table 4 for details. Temperature Sense-Voltage Input from external thermistor. The thermistor temperature coefficient is negative, so the higher the temperature, the lower the voltage at this pin (See Detailed Description for conditions of operation). Input Voltage of Single Battery Cell. If more than one cell is present, a resistor divider is needed to divide the voltage down to a single cell voltage. Ground Current-Sense Input--connected to the negative battery terminal. TS and BAT are referenced to this pin. The voltage at SNS is directly proportional to the current through the battery and is used to determine how and when MOD switches. Temperature Cutoff-Voltage Input. If the voltage from TS to SNS is less than the voltage at TCO, a hot thermistor (negative coefficient) is detected and fast or top-off charging is terminated. Maximum Cell Voltage Input. If the voltage from BAT to SNS exceeds the voltage at MCV, fast or top-off charging is terminated. Temperature Status Output. This push/pull LED driver indicates that the temperature is outside the acceptable limits, and fast-charge and top-off are inhibited (see Maximum Temperature Termination section in Detailed Description). Charge Status Output. This push/pull LED driver indicates charge status (see Detailed Description). Modulation Output. This push/pull output switches to enable or disable charging current. If MOD is high, current is enabled. If it is low, current is disabled. For a 5V supply, if the voltage at the SNS pin is less than 220mV, MOD is high. If the voltage is above 250mV, MOD is low. Discharge-Switch Control Output. This push/pull output turns on the FET that discharges the battery. Power-Supply Voltage Input (+5V nominal). Bypass with a 0.1F capacitor placed close to the device.
1
2 3 4, 5
6
7 8 9
BAT VSS SNS
10 11
TCO MCV
12 13 14 15 16
TEMP CHG MOD DIS VCC
4
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13V/2A DC SOURCE
RTR 10k (*150 (2W)) *TRICKLE-CHARGE RATE C/40
IN LM317 ADJ 0.1F 22F 10k 1N5819 VCC 10V ZENER G 1N5822 CHARGE RATE 1C
5V OUT
Q1 P MMDF3P03HD S D 100H 1N5822
22F 0.1F
22F
243 732
0.1F 1F 14 MOD 14 1, 3, 5 74HC04 9, 11, 13 7 2, 4, 6 8, 10, 12 D DIS S TS 6 RT 100k 1k LED 12 13 CHG SNS MCV CB 0.1F 10 TC0 VSS 8 BAT 7 RB 100k 9 11 LED 1k TEMP R1 60.4k R2 3.48k R3 33.2k CT 0.1F RT2 15 G Q2 N MMSF5NO3HD VCC PUSH TO DISCHARGE 16 5 TM2 TM1 4 VCC RDIS 4 (20W) TO VCC
RB1 100k
DISCHARGE RATE 1C DURACELL DR17 RT1 1700mAh 6 NiMH
RB2 20k
Figure 1. Switched-Mode Operation for NiMH Batteries with T/t Termination
2 DCMD CCMD DVEN 1 100k 3
MAX2003 MAX2003A
NTC
RSNS 0.14 1% (1W)
MAX2003/MAX2003A
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* COMPONENT USED FOR MAX2003.
NiCd/NiMH Battery Fast-Charge Controllers
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NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
Detailed Description
The MAX2003/MAX2003A is a fast-charge battery charger that uses several methods of charge termination. The device constantly monitors your choice of the following conditions to determine termination of fast-charge: * Negative Delta Voltage (-V) * Rate-of-Change of Temperature (T/t) * Maximum Voltage * Maximum Time * Maximum Temperature Figure 2 shows the block diagram for the MAX2003/ MAX2003A. The first step in creating a fast-charge battery-charger circuit is to determine what type of battery will be used and what conditions the battery manufacturer recommends for termination of fast-charge. The type of battery (NiCd or NiMH) and charge rate determine which method(s) of termination should be used. The charging characteristics of NiMH batteries are similar to those of NiCd batteries, but there are some key differences that affect the choice of charge-termination method. Since the type of charge termination can be different for NiCd and NiMH batteries, it may not always be possible to use the same circuit for both battery types. A comparison of the voltage profiles for NiCd and NiMH batteries (shown in Figure 3) reveals that NiCd batteries display a larger negative drop in voltage at the end of charge than do NiMH batteries. Therefore, the negative delta voltage detection (-V) method of terminating fast-charge should only be used for NiCd batteries. This termination method can cause errors in NiMH batteries, since the drop in voltage at full capacity is not as great, and may lead to an overcharged battery. Figure 4 shows the temperature profiles of the two types of batteries. During the first 80% of the charge cycle, the NiCd battery temperature slowly rises. The NiMH battery temperature rises more rapidly during this period. As the cells approach 90% of capacity, the temperature of the NiCd cells rises more rapidly. When the cells approach full capacity, the rates-of-rise of temperature are comparable for both battery types. The rate of temperature change (T/t) can therefore be used to terminate fast-charge for both NiCd and NiMH batteries; fast-charge is terminated when the rate of temperature rise exceeds a preset rate. Table 1 provides some guidelines to help in the selection of the proper fast-charge termination method, but the manufacturer's recommendations take priority in case of conflict.
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Table 1a. Fast-Charge Termination Methods for NiMH Batteries
Charge Rate >C/2 T/t Yes Negative V No Max Voltage Yes Max Time Yes Max Temp. Yes
Table 1b. Fast-Charge Termination Methods for NiCd Batteries
Charge Rate >2C 2C to C/2 T/t Yes Negative V Yes Max Voltage Yes Yes Max Time Yes Yes Max Temp. Yes Yes
*
*
* Use one or both of these termination methods.
Figure 1 shows a standard application circuit for a switched-mode battery charger that charges NiMH batteries at a rate of C. Though this circuit is shown for NiMH batteries, it can be used for NiCd batteries (see Table 1b). The description below will use this standard application to explain, in detail, the functionality of the MAX2003/MAX2003A.
Battery Sense Voltage
The BAT pin measures the per-cell voltage of the battery pack; this voltage is used to determine fast-charge initiation and termination. The voltage is determined by the resistor-divider combination RB1 and RB2, shown in Figure 1, where: Total Number of Cells = (RB1 / RB2) + 1 Since BAT has extremely high input impedance (50M minimum), reasonable values can be selected for resistors RB1 and RB2. These values, however, must not be low enough to drain the battery or high enough to unduly lengthen the time constant of the signal going to the BAT pin. The total resistance value from the positive to negative terminal of the battery (RB1 + RB2) should be between 100k and 500k to prevent these problems. A simple RC lowpass filter (RB, CB) may be needed to give a more accurate reading by removing any noise that may be present. Remember that the RC time delay from the cell to BAT must not exceed 200ms or the battery detection logic might not function properly (R B x CB < 200ms).
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NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
TM1 TM2 VCC
OSC
TIMING CONTROL
LTF CHECK
TCO CHECK
MAX2003 MAX2003A
TCO
TEMP CHG
DISPLAY CONTROL (VTS - VSNS)
CCMD DCMD DVEN
CHARGE CONTROL STATE MACHINE
- -
+
TS SNS
A/D (VBAT - VSNS)
+
BAT
DISCHARGE CONTROL
MOD CONTROL
EDV CHECK
MCV CHECK
MCV
DIS
MOD
VSS
Figure 2. Block Diagram
MAX2003-03
NiCd 1.8 VOLTAGE/CELL (V) 1.6 NiMH 1.4 1.2 1.0 0.8 0 20 40 60 80 100
NiMH 50 45 TEMPERATURE (C) 40 35 NiCd 30 25 20 15
120
0
20
40
60
80
100
120
CHARGE CAPACITY (% OF MAXIMUM)
CHARGE CAPACITY (% OF MAXIMUM)
Figure 3. Voltage-Charge Characteristics of NiCd and NiMH Batteries
Figure 4. Temperature-Charge Characteristics of NiCd and NiMH Batteries
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MAX2003-04
2.0
55
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
Temperature Measurement
The MAX2003/MAX2003A employs a negative temperature-coefficient (NTC) thermistor to measure the battery's temperature. This temperature value can be used to determine start and termination of fast-charge. The two temperature conditions that can be used for fastcharge termination are: * Maximum Temperature * Rate-of-Change of Temperature (T/t) Figure 5 shows the various temperature cutoff points and the typical voltages that the device will see at the TS pin. VLTF (low-temperature fault voltage) refers to the voltage at TS when the battery temperature is too low, and VHTF (high-temperature fault voltage) refers to the hightemperature cutoff. If the voltage is outside these limits, the MAX2003/MAX2003A will not enter fast-charge mode. After fast-charge is initiated, the termination point for high-temperature termination is VTCO (temperature cutoff voltage), rather than VHTF. See Figure 5 for TEMP LED status. VLTF is set internally at 0.4VCC, so (with a 5V supply) VLTF is 2V. VTCO is set up using external resistors to determine the high-temperature cutoff after fast-charge begins. VHTF is internally set to be (VLTF - VTCO) / 8 above VTCO. Thermistors are inherently nonlinear with respect to temperature. This nonlinearity is especially noticed when T/t measurements are made to determine charge termination. The simplest way around this is to place a resistor-divider network in parallel with the thermistor (Figure 6) to reduce the effects of nonlinearity. The lowpass filter (RT, CT) placed on the TS pin attenuates high-frequency noise on the signal seen by TS.
TEMP LED STATUS
Charge Pending
Before fast-charge is initiated, the cell voltage and temperature of the battery pack must be within the assigned limits. If the voltage or temperature is outside these limits, the device is said to be in a "charge-pending" state. During this mode, the CHG pin will cycle low (LED on) for 0.125sec and high (LED off) for 1.375sec. Fast-charge is normally initiated if the cell voltage is greater than VEDV (end-of-discharge voltage). If the cell voltage is too low (below VEDV), the device waits until the trickle current brings the voltage up before fastcharge is initiated. VEDV is set internally at 0.2VCC, so (for a 5V supply) VEDV is 1V. If the temperature of the cell is not between VLTF and VHTF the device is also in a charge-pending state (see Temperature Measurement section).
Initiate Fast-Charge
If the MAX2003/MAX2003A are out of the charge-pending state, fast-charge can be initiated upon one of the following conditions: * Battery Replacement * Applying Power to the MAX2003/MAX2003A (battery already present) * Digital Control Signal During fast-charge, the CHG pin will be continuously low (LED on). For the initial period of fast-charge (the hold-off time), the voltage charge-termination methods are disabled. The hold-off time is a function of the charge rate selected by TM1 and TM2 (see Table 4).
VCC = 5V RT1
VCC
ON
RC FILTER 100k TS
MAX2003 MAX2003A
VLTF = 0.4VCC OFF 7/8 (VLTF - VTCO) VHTF ON 1/8 (VLTF - VTCO) VTCO VSS = 0V VLTF - VTCO RT2 NTC
RT CT 0.1F
SNS
Figure 5. Temperature Measurement Scale
8
Figure 6. Thermistor Configuration for Temperature Measurement
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NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
Table 2. Device Status on Power-Up if Battery is Already Present
CCMD Low DCMD Low MAX2003/MAX2003A Status when Power is Applied * Fast-charge is initiated on power-up. * The device does not enter fast-charge immediately. * Fast-charge is initiated by the falling edge of a pulse on CCMD. * The device does not enter fast-charge immediately. * Fast-charge is initiated by the rising edge of a pulse on CCMD. * Fast-charge is initiated on power-up. Low High * Fast-charge is initiated by a rising edge on CCMD. * Fast-charge is initiated by a falling edge on CCMD.
Table 3. Digital Control of Fast-Charge (VCC and battery present)
CCMD DCMD CCMD Status to Initiate Fast-Charge
Low
High
High
Low
Discharge-Before-Charge (optional)
The discharge-before-charge function is optional and can be used to condition old batteries. It is especially useful in NiCd batteries, since it alleviates the voltage depression problems associated with partially discharged NiCd cells. The discharge-before-charge function is initiated by a rising edge into DCMD. When the digital signal is applied, the DIS pin will be pulled high, turning on the attached circuit and discharging its battery. The discharge process continues until the single cell voltage drops below 0.2VCC. During the discharge phase, the CHG pin will be low (LED on) for 1.375sec and high (LED off) for 0.125sec. The MAX2003/MAX2003A does not control the current during discharge-before-charge. If the discharge rate is too great, the battery could overheat and be damaged. The battery manufacturer will be able to specify a safe discharge rate, but a rate of C or slower is typically acceptable. It is also important to choose components (Q2, R DIS ) that are rated for that particular discharge rate. Since the gate-source drive for Q2 can be as low as 4.5V, use a logic-level MOSFET.
High
High
Battery Replacement Before a battery is inserted, the BAT pin is pulled higher than the maximum cell voltage (MCV) by the resistor (RTR) and the divider network (RB1/RB2) (Figure 1). When the battery is inserted, the voltage per cell at BAT falls from the default voltage to the battery voltage. Fast-charge is initiated on a falling edge when the BAT voltage crosses the voltage on MCV. Applying Power to the MAX2003/MAX2003A (battery already present) There may be some cases where a battery is connected before power is applied to the MAX2003/ MAX2003A. When power is applied, the device goes into reset mode for approximately 1.5sec and then samples the CCMD and DCMD pins. Its charge status is determined by the voltage at both the CCMD and DCMD pins. Table 2 summarizes the various conditions the MAX2003/MAX2003A might see on power-up. Table 2 shows that the MAX2003/MAX2003A can be set-up for fast-charge on power-up by making sure CCMD and DCMD are at the same potential. If fastcharge on power-up is not desired, make sure CCMD and DCMD are at different logic levels during powerup, and use a digital signal to control fast-charge (see Digital Control section). Digital Control The CCMD pin can be used to initiate fast-charge. This is useful when neither the power supply nor the battery can be removed from the charger. The CCMD signal needed to initiate fast-charge depends on the potential at DCMD. If DCMD is low, a rising edge on CCMD initiates fastcharge. If DCMD is high, a falling edge on CCMD provides the fast-charge signal. Table 3 summarizes the conditions used to start fast-charge.
Fast-Charge Current
The fast-charge current can be generated using two categories of circuits: * Circuits with a sense resistor (RSNS) * Circuits without sense resistor (SNS tied to VSS)
Circuits with SNS Resistor The standard application circuit of Figure 1 uses an inductor and a switched mode of operation to supply the current. The charge current is determined by the sense resistor placed between the negative terminal of the battery (SNS) and ground (VSS). The SNS pin is the input to a comparator with hysteresis. If the voltage at SNS drops below 0.044VCC, the MOD pin is turned on. If the SNS voltage is above 0.050VCC, MOD is turned off. In the switched mode of
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9
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
operation, the SNS voltage ramps between 0.044VCC and 0.050VCC, which is 220mV and 250mV when VCC is 5V (Figure 7). The average voltage at SNS, therefore, is 235mV, and can be used to calculate the charge current as follows: ICHARGE = 0.235V / RSNS where RSNS is the sense resistor and ICHARGE is the charge current required.
Circuits without SNS Resistor In some applications (shown later), SNS is tied directly to ground. In these cases, the MOD pin remains on until any one charge-termination condition is exceeded (Figure 8). A reasonable external current limit (such as a current-limited DC source) must be provided for these applications, to prevent battery damage due to excessive charge currents.
Charge Termination
The MAX2003 has several charge-termination methods. The termination method selected depends on the type of battery and charge rate used. Table 1 summarizes the conditions used to terminate fast-charge with different battery types and charge rates.
Temperature Rate Termination The Temperature Rate Termination (T/t) method terminates fast-charge when a particular rate-of-change in temperature is exceeded. As the battery begins fastcharge, its temperature increases at a slow rate. When the battery nears full capacity, this rate of temperature change increases. When the rate of temperature change exceeds a preset number, fast-charge is terminated. This method of fast-charge termination can be used for both NiCd and NiMH batteries. The MAX2003 samples the voltage at the TS pin every 34 seconds and compares it with a value taken 68 seconds earlier. Since an NTC thermistor is used for temperature measurements, a gradual rise in temperature will result in successively lower voltage readings. If the new reading is more than 0.0032VCC (16mV for VCC = 5V) below the old reading, fast-charge is terminated. The MAX2003A varies the sampling interval as a function of charge rate (Table 4). As the charge rate increases, the sampling interval decreases, thereby allowing more accurate termination of fast charge. Note: This method of charge termination is valid only when the battery's temperature is between VLTF and VTCO (Figure 5).
FAST CHARGE FAST-CHARGE TERMINATE
MOD VCC
FAST CHARGE
FAST-CHARGE TERMINATE
MOD VCC
0 SNS 0.050 VCC 0.044 VCC 0 IBAT
TIME
0 SNS 0.050 VCC 0.044 VCC SNS = 0V
TIME
TIME
0 IBAT
TIME
ILOAD
ILOAD
0
TIME
TIME
Figure 7. Current Regulation with an SNS Resistor
10
Figure 8. Current Regulation without an SNS Resistor
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NiCd/NiMH Battery Fast-Charge Controllers
Negative Delta Voltage Termination The Negative Delta Voltage Termination (-V) method measures a negative delta voltage to determine termination of fast-charge. After maximum charge is reached, the terminal voltage of NiCd batteries declines significantly, whereas the terminal voltage of NiMH batteries does not. Hence, the -V method of fast-charge termination is suitable for NiCd batteries, but not for NiMH batteries. The MAX2003/MAX2003A sample the BAT pin every 34 seconds and compare it with all previous values. If the new value is less than any of the previous values by more than 12mV, a negative delta voltage has been detected and fast-charge is terminated. Note: This method of charge termination is valid only when the voltage at BAT is between VMCV and VMCV 0.2VCC. The -V method is inhibited during the hold-off time to prevent false termination of fast-charge. The hold-off time depends on the charge rate used, and is selected by the inputs TM1 and TM2 (as shown in Table 4). After the hold-off time has expired, the device begins to monitor BAT for a voltage drop. Maximum Temperature Termination The Maximum Temperature Termination method is used as a safety net to prevent problems, and should never be needed under normal operation of the charger. The maximum temperature that the battery can reach during fast-charge has a corresponding voltage--the temperature cutoff voltage (VTCO), as seen in Figure 5. This voltage is set externally at the TCO pin using a resistor divider from V CC . Although rarely experienced, an excessively low temperature will also terminate fastcharge. The minimum temperature is the low temperature fault (VLTF). This value is internally set at 0.4VCC. When the thermistor exceeds these temperature limits, fast-charge is terminated. The thermistor configuration shown in Figure 5 is used to measure the battery's temperature and scale it to operate from V LTF to VTCO. Resistors RT1 and RT2 are calculated to provide the required cutoff at VTCO. See the Design Guide section for a detailed design example. Maximum Voltage Termination The Maximum Voltage Termination method is another safety feature designed to work if something is drastically wrong. Under normal operation of the charger, this condition should only be reached when the battery is removed. The maximum cell voltage expected is applied at the MCV pin using a resistor-divider network. If the cell voltage measured at BAT exceeds that at MCV, fastcharge is terminated. For most applications using both NiCd and NiMH batteries, this voltage (VMCV) can be set to 1.9V. The MAX2003/MAX2003A do not terminate fast-charge if the maximum voltage is reached before the hold-off time has expired. If the cell voltage is greater than the MCV during the hold-off time, the device will continue fast-charge until the hold-off time has expired, and then it will terminate fast-charge. The hold-off time is determined by the inputs TM1 and TM2, as shown in Table 4.
MAX2003/MAX2003A
Maximum Timeout Termination The final method is Maximum Timeout Termination, which (like the maximum voltage and maximum temperature methods) is another backup safety feature. The timeout time depends on the charge rate selected and is set by the control signals TM1 and TM2. Table 4 shows a list of different timeout periods available for different control-signal inputs. If the timeout is reached before any other termination method is seen, fastcharge is terminated to protect the charger and battery.
Top-Off Charge
Top-off charge is used to provide the last bit of charge needed to reach full capacity after fast-charge is terminated. Top-off charging puts slightly more energy into the battery than simple trickle charging, and can be used for both NiCd and NiMH batteries. Select it by choosing the appropriate control signals on TM1 and TM2 (Table 4).
Table 4. Programmable Inputs for Timeout/Hold-Off/Fast-Charge/Top-Off/ Pulse Trickle (VCC = 5V)
TM1 Fast- Hold-Off MAX2003A MAX2003A FastCharge Time Top-Off Trickle Sampling TM2 Charge Timeout V/MCV Charge Charge (s) Interval Rate (min) (sec) On/Off (sec) GND C/4 C/2 C 2C 4C C/2 C 2C 4C 360 180 90 45 23 180 90 45 23 140 820 410 200 100 820 410 200 100 Disable Disable Disable Disable Disable *Enable *Enable *Enable *Enable Disable 1 1 1 1 0.5 0.5 0.5 0.5 16 32 64 128 16 32 64 128 544 544 136 68 68 544 136 68 68
GND
Open GND VCC GND
GND Open Open Open VCC GND Open VCC Open VCC VCC VCC
* MAX2003 is on for 4sec and off for 30sec. MAX2003A is on for 0.5sec and off for 3.5sec.
11
______________________________________________________________________________________
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
Table 5. Charge Status
Charge State Battery Absent Charge Pending Discharge-Before-Charge Fast-Charge Charge Complete and TopOff CHG LED Status LED off LED on for 0.125sec, off for 1.375sec LED on for 1.375sec, off for 0.125sec LED on LED on for 0.125sec, off for 0.125sec
The top-off charge is done at 1/8 the fast-charge rate. For the MAX2003, the MOD pin is activated in every 34 second period to supply current to the battery for 4 seconds (MOD oscillates for 4 seconds and stays low for 30 seconds) (Figure 7). If external regulation is used (SNS tied to ground), MOD stays high for 4 seconds and low for 30 seconds (Figure 8). This top-off process continues until the fast-charge timeout (Table 4) is exceeded, or if a maximum temperature or maximum voltage condition is detected. The MAX2003A is slightly modified to turn the MOD pin on for 0.5sec in every 4 second period. This shorter on-time reduces battery heat and increases charge acceptance. During the topoff charge, the CHG pin will cycle low (LED on) for 0.125sec and high (LED off) for 0.125sec.
would be C/16, and NiMH batteries could use a rate of C/40. The resistor value used depends on the maximum DC voltage and the typical battery voltage. For example, a six-cell 800mAh NiCd pack with a nominal voltage of 1.2V per cell would have a total voltage of 1.2V x 6V = 7.2V. If the DC supply voltage used is 14V, the voltage across the trickle resistor would be 14.0V 7.2V = 6.8V. The trickle current needed would be C/16 = 800 / 16 = 50mA. The trickle resistor would therefore be RTR = 6.8V / 50mA 150. Similar calculations should be made for NiMH batteries using C/40 as the trickle-charge rate. If a trickle-charge is not needed, a higher value of trickle resistor (like 100k) can be selected to sense the battery insertion.
Charge Status
The CHG pin is connected to a LED that indicates the operating mode. Table 5 summarizes the different charge conditions.
_______________________Design Guide
Using the circuit of Figure 1 as an example, the following nine steps show how to design a 1.7A switch-mode fast-charger that can charge a Duracell DR17 (NiMH six-cell battery pack with a 1700mAh capacity). 1) Select DC Power Supply. The first step is to select the DC power supply (such as a wall cube). The minimum supply voltage should have a supply equal to about 2V per cell, plus 1V headroom for external circuitry ((2V/cell) + 1V). The minimum supply voltage must be greater than 6V. If, as in our example, there are six cells, a minimum supply of about 13V is needed ((6 cells x 2V) + 1V). 2) Determine Charge Rate. The charge rate, or fastcharge current (IFAST), is determined by two factors: the capacity of the battery, and the time in which the user wants the battery to be charged. The battery manufacturer recommends a maximum fast-charge rate, which must not be exceeded. Capacity of Battery (mAh) IFAST (mA) = ------------------------ Charge Time (h) For example, if a 1700mAh battery needs to be charged in two hours (C/2), a fast-charge current of at least 850mA is needed. A charge rate of C/2 will ideally charge a battery in two hours but, because of inefficiencies in a battery's chemical processes, the time could be 30% to 40% more. Our example circuit (Figure 1) charges the Duracell battery pack at a C rate of 1.7A, which should fully charge a discharged battery in approximately 80 minutes.
Trickle-Charge
A trickle-charge is applied to the battery after fastcharge and top-off charge have terminated to compensate for self discharge. There are two methods of trickle charge: constant and pulsed.
Pulsed Trickle-Charge (MAX2003A)
The MAX2003A provides a pulsed trickle-charge to the battery by turning on the MOD pin briefly during a fixed period of time. The duty cycle of the pulse is a function of the programmable inputs TM1 and TM2 (Table 4 ). The MAX2003A does not use the trickle resistor to provide the trickle charge. However, the trickle resistor cannot be entirely omitted because it is also used for the batterydetect circuitry.
Constant Trickle-Charge (MAX2003)
The MAX2003 provides a steady trickle-charge to the battery by connecting a resistor from the DC supply to the positive battery terminal. This resistor has a dual purpose, in that it provides a trickle-charge and pulls the BAT pin above the MCV when the battery is absent. The trickle-charge rate depends on the type of battery used. For NiCd batteries, a nominal trickle-charge rate
12
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NiCd/NiMH Battery Fast-Charge Controllers
3) Select Sense Resistor. The sense resistor determines the rate at which the battery is fast-charged. The sense pin, SNS, has an average voltage of 235mV (see Detailed Description) and, since the charge current (IFAST) is known from above, the resistor can be calculated by: RSNS = VSNS / IFAST = 0.235 / IFAST In this example, a fast-charge current of 1.7A requires a sense resistor of about 0.14 (1 watt). 4) Select TM1 and TM2. Once the charge rate is determined, Table 4 can be used to select the TM1 and TM2 inputs. TM1 and TM2 set the safety timeout, holdoff time, and top-off enable (see Fast-Charge Termination section in the Detailed Description). In Figure 1, a fast-charge rate of C with top-off would require TM1 to be GND and TM2 to be VCC. 5) Select RB1 and RB2. The MAX2003A requires the user to select RB1 and RB2 to indicate the number of cells in the battery. The total resistance value (RB1 + RB2) should be between 100k and 500k to prevent any problems with noise. In Figure 1 (with six cells) RB1 is selected to be 100k and, from the following equation: RB2 = RB1 / (Number of Cells - 1) = 100k / (6 - 1) RB2 can be calculated to be 20k. 6) Select Temperature-Control Components. Most sealed rechargeable battery packs have a built-in thermistor to prevent air currents from corrupting the accurate temperature measurements. The thermistor size and temperature characteristics can be obtained from the battery-pack manufacturer, to help in designing the rest of the circuit. Three-terminal battery packs that incorporate a thermistor generally share a common connection for the thermistor and the battery negative terminal. Large charging currents may produce voltage drops across the common negative connector, causing errors in thermistor readings. Using separate contacts for the thermistor ground sense and the battery ground sense at the negative battery terminal will reduce these errors. If an external thermistor is to be used, take care to ensure that it is placed in direct contact with the battery, and that the battery/thermistor set-up is placed in a sealed container. Neither NiCd nor NiMH batteries should be fastcharged outside the maximum and minimum temperature limits. However, some applications also require termination using the T/t criterion. The resistors RT1 and RT2 (Figure 1) will determine the temperature cutoff (VTCO) and the rate-of-change of temperature (T/t). Though NiCd batteries do not always require termination using the T/t feature, it is not possible to isolate and disable this mode. It is therefore recommended that NiCd and NiMH batteries use the same T/t termination parameters. The Duracell DR17 battery pack used in our example circuit recommended a low fault temperature (VLTF) of +10C and a maximum temperature cutoff (V TCO) of +50C. These maximum temperature values will never be reached in most cases, but are used as a safety net to prevent battery damage. According to Duracell, the 10k thermistor inside the pack varies from 17.96k at +10C to 4.16k at +50C. The circuit in Figure 1 will be designed so that a battery temperature change of 1C/min will result in fast-charge termination. At 1C/min, the battery will take 40 minutes to change 40C (10C to 50C). Since a charge rate of C is used for this example, Table 4 shows that the MAX2003A samples the TS pin every 68 seconds and compares it with a value taken 136 seconds earlier. The device will terminate fast-charge if the voltage at TS changes by more than 0.0032VCC (16mV for VCC = 5V). At a charge rate of 16mV every 136 seconds, the TS pin will charge 280mV in 40 minutes (40min x 60sec/min x 16mV/136sec). The low fault temperature (VLTF) is set internally at 0.4VCC, which is 2.0V for a supply of 5V. The temperature cutoff voltage (VTCO) will be 280mV below VLTF, or: VTCO = (2.00V - 0.28V) = 1.72V Figure 5 shows that, at any given temperature: VTS = VCC (RT2 || RNTC) / [(RT2 || RNTC) + RT1] When the battery temperature is +10C, the voltage is: VTS10 = VCC (RT2 || RNTC10) / [(RT2 || RNTC10) + RT1] And at +50C: VTS50 = VCC (RT2 || RNTC50) / [(RT2 || RNTC50) + RT1]
VCC
MAX2003/MAX2003A
R1 MCV R2 TCO R3
Figure 9. Resistor Configuration for MCV and TCO
13
______________________________________________________________________________________
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
From solving these simultaneous equations: RT2 = [(X) (RNTC10) - (RNTC50)] / (1 - X) RT1 = [(RT2) (RNTC10) (VCC - VTS10)] / [VTS10 (RT2 + RNTC10)]. [(RNTC50)(VTS10)(VCC - VTS50)] where X = _____________________________ [(RNTC10) (VTS50) (VCC - VTS10)] Using RNTC50 = 4.16k, RNTC10 = 17.96k, VTS50 = 1.72V, and VTS10 = 2.00V, it can be calculated that RT1 = 1.599k and RT2 = 2.303k. Select preferred resistor values for RT1 (2.21k) and RT2 (1.62k). The actual voltages on MCV and TCO can be verified as follows: VTS10 = = 8) Select Trickle Resistor (MAX2003 only). The trickle resistor (RTR) is selected to allow a trickle-charge rate of C/16 to C/40. The resistor value is given by: RTR = (VDC - VBAT) / ITR where ITR is the required trickle current, VDC is the DC supply voltage, and VBAT is the number of cells times the cell voltage after fast-charge. In our example, the 1700mAh NiMH battery needs a trickle current of C/40; i.e., 42mA (1700mAh/40h). Therefore, the minimum voltage (from the formula above) is as follows: RTR = [13.0V - (6 x 1.2V)] / 42mA 150 The maximum power dissipated in the resistor can be calculated by: Power = (VDC - VBAT(MIN))2 / RTR where VBAT(MIN) is the minimum cell voltage, VDC is the DC supply voltage, and RTR is the trickle resistor value. Since a shorted battery could have 0V, this must be the minimum cell voltage possible. Therefore the power dissipated in the trickle resistor would be: Power = (13 - 0)2 / 150 = 1.2W A 2W, 150 resistor should be sufficient for the tricklecharge resistor. For the MAX2003A, refer to TrickleCharge section. 9) Select Inductor. The inductor value can be calculated using the formula: VL = L / it where VL is the maximum voltage across the inductor, L is the minimum inductor value, is the change in induci tor current, and t is the minimum on-time of the switch.
[(R T2 II RNTC10 ) + R T1] [(
5 1.62k II 17.96k
VCC R T2 II RNTC10
(
)
(
1.62k II 17.96k + 2.21k VCC R T2 II RNTC50
)
)
= 2.01V VTS50 = =
]
[(R T2 II RNTC50 ) + R T1] [(
5 1.62k II 4.16k
(
)
(
1.62k II 4.16k + 2.21k
)
)
= 1.72V
]
7) Select Maximum Cell Voltage (MCV) and Temperature Cutoff (TCO). The MCV and TCO can be selected with a resistor-divider combination (Figure 9). In our example, TCO has been set to +10C, which corresponds to a voltage of 1.72V at the TS pin. The MCV for most fast-charge batteries can be set to about 1.9V. To minimize the current load on VCC, choose R1 in the range of 20k to 200k. In this example, choose R1 = 60.4k, then calculate R3 and R2 as follows: R3 = (VTCO x R1) / (VCC - VMCV) = 33.5k (1%) and R2 = (VMCV x R1) / (VCC - VMCV) - R3 = 3.51k (1%) Select preferred resistor values for R2 (3.48k) and R3 (33.2k). The actual voltages on MCV and TCO can be verified as follows : VTCO = VCC (R3) / (R1 + R2 + R3) = 1.71V and VMCV = VCC (R2 + R3) / (R1 + R2 + R3) = 1.89V.
14
INDUCTOR CURRENT
i = IMAX - IMIN
IMAX = 1.9A ILOAD IMIN = 1.5A
tOFF
tON
TIME
Figure 10. Inductor-Current Waveform in ContinuousConduction Mode
______________________________________________________________________________________
NiCd/NiMH Battery Fast-Charge Controllers
In order to provide high currents with minimum ripple, the device must function in the continuous-conduction mode. Figure 10 shows a current waveform of an inductor in the continuous-conduction mode (where the coil current never falls to zero). The average load current (ILOAD) through the inductor must be 1.7A, so a peak current (IMAX) of 1.9A should give a fairly low ripple while keeping the inductor size minimal. This means that the total current change (Figure 10) across the inductor is = 2 (1.9 - 1.7) = 0.4A. i The maximum voltage across the inductor is present when the battery voltage is at its minimum. The minimum cell voltage at the start of fast-charge will be 1V per cell, giving a battery voltage of 6V for 6 cells. The maximum voltage (VL) across the inductor is therefore: VL = (input voltage - minimum battery voltage) The input voltage for this application is 13V, so the maximum voltage is: VL = (13V - 6V) = 7V The minimum on-time of the switch is given by: t = (VOUT / VIN ) x PERIOD t where VOUT is the minimum battery voltage, VIN is the maximum input voltage, and PERIOD is the period of the switching signal. The maximum input voltage for this application will be 14V, and the maximum allowed switching frequency of 100kHz gives a period of 10s. The minimum on-time will therefore be: = (VOUT / VIN ) x PERIOD = (6V / 13V) x 10s = 4.62s t The inductor value can be calculated from: L = V / = (7V x 4.62s) / 0.4A = 81H. ti If this inductor value is used, the actual switching frequency will be lower than the 100kHz expected, due to comparator delays and variations in the duty cycle. The inductor value selected for our application will be 100H--a preferred value just above the calculated value. It is important to choose the saturation current rating of the inductor to be a little higher than the peak currents, to prevent the inductor from saturating during operation. The inductor must be selected to ensure that the switching frequency of the MOD pin will not exceed the 100kHz maximum.
MAX2003/MAX2003A
Additional Applications _________________________Information
The MAX2003/MAX2003A can use several other circuits to charge batteries. Figure 9 shows a circuit that uses a Darlington transistor to regulate the current a six-cell NiCd battery pack receives. Figure 10 shows a gated current-limited supply being used to charge a Duracell NiMH battery pack. Table 6 lists the external components used in these two application configurations.
Linear Regulation of Charge Current
The circuit in Figure 11 uses an inexpensive transistor to provide the charge current. Since the input for the MAX667 can tolerate up to 16V, this circuit can charge up to 7 cells. The MAX667 can be replaced with a different regulator if more cells need to be charged. The DC source must supply a voltage equal to 2x the number of cells, plus 2V overhead to accommodate the drop across external components. When fast-charge is initiated, the voltage at the SNS pin is sampled and compared to the trip levels (220mV low and 250mV high). If the voltage at SNS is below 220mV, the MOD pin will switch high, and the 10k/1F RC lowpass filter will pull high, turning on the NPN transistor. This will pull the base of the Darlington TIP115 low, turning it on and allowing current to flow into the battery. When the current through the battery and SNS resistor are high enough, the voltage at SNS will exceed 250mV and the MOD pin will turn off. The amount of current the battery receives depends on the resistor between SNS and VSS. In our example circuit, the average current through the SNS resistor will be: ISNS(AVG) = VSNS(AVG) / RSNS = 0.235 / 0.28 = 0.84A The maximum current the resistor will receive is: ISNS(MAX) = VSNS(MAX) / RSNS = 0.25 / 0.28 = 0.90A The Darlington transistor must be biased to ensure that a minimum of 0.90A will be supplied. This minimum
15
Table 6. External Component Sources
Device Power Supply Thermistor Power MOSFET & Darlington Transistor Manufacturer Phone Number Advanced Power Solutions Alpha Thermistor (510) 734-3060 (800) 235-5445 Fax Number (510) 460-5498 (619) 549-4791
Motorola
(602) 303-5454
(602) 994-6430
Battery
Duracell Energizer Power Systems
(800) 431-2658 (904) 462-3911
(203) 791-3273 (904) 462-4726
______________________________________________________________________________________
MAX2003/MAX2003A
NiCd/NiMH Battery Fast-Charge Controllers
Figure 11. Linear Mode to Charge NiCD Batteries with -V Termination
14V/2A DC SOURCE Q1 1 2 47F 4 5 10k 3 7 TIP115 HEATSINK 0.1F 47F CHARGE RATE 1C 8 IN 1N5822 RTR 10k (*150 (2W)) *TRICKLE-CHARGE RATE C/16
16
5V OUT
0.1F
MAX667
6
VCC
6.8k
0.1F 16 3 DVEN TM2 TM1 S DCMD CCMD TS 6 RT 100k CT 0.1F SNS 9 RT2 1.62k RT1 2.21k DIS 15 G Q2 N MMSF5NO3HD D MOD 14 5 4 VCC 1F RDIS 9 (10W) Q3 2N2222 PUSH TO DISCHARGE
10k
DISCHARGE RATE 1C
RB1 100k
TO VCC
2 1 100k
800mAh 6 NiCd
NTC ALPHA CURVE A THERMISTOR RB2 20k
1k LED 12 TEMP CHG MCV 13 11 R2 3.48k 10 TC0 VSS 8 BAT 7 R3 33.2k LED 1k
MAX2003 MAX2003A
R1 60.4k
______________________________________________________________________________________
CB 0.1F RB 100k RSNS 0.294 1% (1W) *COMPONENT USED FOR MAX2003.
ILIMITED VSOURCE OUT Q1 P MMDF3P03HD D S 1N5822 10k G 12V ZENER 0.1F 22F VCC 1k CHARGE RATE 1C *TRICKLE-CHARGE RATE C/40
19V
RTR 10k *180 (2W)
2.6A IN LM317 ADJ 5V OUT
22F
0.1F
22F
243 732
0.1F Q3 2N2222 RDIS 4 (20W) D TM1 DIS 15 TO VCC RT1 2.21k G DCMD CCMD DVEN TS 6 100k CT 0.1F SNS 9 RT Q2 N S MMSF3N03HD DISCHARGE RATE 1C PUSH TO DISCHARGE 5 TM2 MOD 14 4 2 1 100k 3 VCC 16
1k
RB1 80.6k
Figure 12. Current-Limited Mode for NiMH Batteries with T/t Termination
DURACELL DR35 2600mAh 9 NiMH NTC RB2 10k RT2 1.62k 1k LED 12 TEMP CHG MCV 13 11 R2 3.48k 10 TC0 VSS BAT 7 R3 33.2k *COMPONENT USED FOR MAX2003. LED 1k CB 0.1F RB 100k R1 60.4k
MAX2003/MAX2003A
______________________________________________________________________________________
MAX2003 MAX2003A
NiCd/NiMH Battery Fast-Charge Controllers
17
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
current value must be sufficiently guardbanded to ensure the limiting factor is the SNS resistor, and not the transistor. In our example, the maximum current supplied by the Darlington will be guardbanded to 1.8A. Since the beta of the Darlington is typically 1000, the base current needed will be: IB = IC / BETA = 1.8A / 1000 = 1.8mA The emitter of the TIP115 will see 14V, so the base will see about 12.6V. When the MOD pin is high, the 2N2222 transistor is on and the base resistor will be: RB = VB / IB = 12.6V / 1.8mA 6.8k This 1.8A current will never be reached because MOD will be off when the SNS voltage reaches 0.25V (0.9A).
Current-Limited Supply
The circuit in Figure 12 is set up to charge a Duracell DR35 battery pack (nine cells, 2.6Ah) using a 19V, 2.6A current-limited power supply provided by Advanced Power Solutions. Since many power supplies have built-in current limiting, very few external components are required for this charging method. The SNS pin in this circuit is tied directly to VSS. This signals the MOD pin to stay high until a termination condition is met. When MOD is high, the NPN transistor is turned on, hence pulling the gate of the MOSFET low. This turns the MOSFET on and supplies current to the battery at the current limit of the source (2.6A). The 12V zener diode is placed between the source and gate of the FET to ensure the FET's maximum source-drain voltage is not exceeded. When a termination condition is reached, the MOD pin goes low to turn off the FET and terminate the fastcharge current.
Table 7. Operation Summary
Charge Status Conditions (VBAT - VSNS) VMCV Rising edge on DCMD a) Power applied and voltage at CCMD = DCMD b ) DCMD = Low, CCMD = Rising Edge (power already present) c ) DCMD = High, CCMD = Falling Edge (power already present) Fast-charge initiated and temperature or voltage outside the set limits. Discharge initiated with temperature and voltage within set limits. Fast-charge initiated with temperature and voltage within set limits. Exceed one of the five termination conditions. Charge complete and top-off enabled without exceeding temperature and voltage limits. Trickle current provided by external resistor after fast-charge/top-off. Pulse current provided by pulsing MOD pin after fast-charge/top-off. MOD Status DIS Status Low Low CHG LED Status LED On LED Off (Low) (High) (sec) (sec) -- Continuous -- Continuous
Battery Absent Initiate Discharge
Low Low
Initiate Fast-Charge
Low
Low
--
Continuous
Charge Pending Discharge Fast-Charge Charge Complete
Low Low If VSNS > 0.050VCC, MOD = Low If VSNS > 0.044VCC, MOD = High Low MAX2003A: Activate for 0.5sec in every 4sec period. MAX2003: Active for 4sec in every 34sec period. Low Pulsed according to charge rate (Table 4).
Low High Low Low
0.125 1.375 Continuous 0.125
1.375 0.125 -- 0.125
Top-Off Charge
Low
0.125
0.125
Constant TrickleCharge (MAX2003) Pulsed TrickleCharge (MAX2003A) 18
Low Low
0.125 0.125
0.125 0.125
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NiCd/NiMH Battery Fast-Charge Controllers
Chip Topography
CCMD DCMD VCC DIS
MAX2003/MAX2003A
DVEN TM1
MOD
CHG TM2 TS
0.089" (2.261mm)
TEMP MCV
BAT
VSS 0.086" (2.184mm)
SNS TCO
TRANSISTOR COUNT: 5514 SUBSTRATE CONNECTED TO VSS
________________________________________________________Package Information
SOICN.EPS
______________________________________________________________________________________
19
NiCd/NiMH Battery Fast-Charge Controllers MAX2003/MAX2003A
___________________________________________Package Information (continued)
SOICW.EPS
20
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PDIPN.EPS

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