回 1\ γ 子 1) 充雹南 IC 揭鼓 MM l1 77 DS1633 DS1633 High–Speed Battery Recharger FEATURES PIN ASSIGNMENT TO–220 • Recharges Lithium, NiCad, NiMH and Lead acid batteries + • Retains battery and power supply limits in onboard memory • Serial 1–wire interface is used to program operating limits • 3-pin TO–220 package • Operating range 0°C to 70°C • Applications include consumer electronics, portable/ cellular phones, pagers, medical instruments, backup memory systems, security systems V BAT GND VCC • Configurable to operate with 5V or 6V supplies PIN DESCRIPTION VCC VBAT GND – Supply Voltage – Battery Output – Ground DESCRIPTION The DS1633 Battery Recharger is designed to be a complete battery charging system for standard charge or trickle charge applications. It can be configured to be used with either 5V or 6V supplies and battery voltages as high as 4.7V (3.7V for 5V supplies). The device is flexible enough to be used with a variety of battery chemistries and celI capacities. It provides timer termination of standard charge and automatically shifts into trickle charge. Battery voltage can be monitored and charging terminated if it exceeds a preset maximum as a safety feature. The output load line can be speci- Copyright 1995 by Dallas Semiconductor Corporation. All Rights Reserved. For important information regarding patents and other intellectual property rights, please refer to Dallas Semiconductor databooks. fied as the usual constant current recharge with a voltage limit or it can be configured to approximate any practical load line. All parameters, such as power supply range, charge current load line, trickle charge rate, and timer setting, are programmed into nonvolatile memory using the battery pin as a 1–wire communication port. To ease the task of configuring the device to specific application needs, Dallas Semiconductor makes available a programming kit, the DS1633K, containing easy–to–use software and hardware for IBM personal computers. 052694 1/11 DS1633 The DS1633 is able to offer this flexibility due to its unique architecture (see Figure 1). The device monitors the battery voltage and adjusts the values of the output impedance (RTH) and open circuit voltage (VOC) it presents to the battery. These values can be adjusted at 32 user definable points (breakpoints) that occur roughly every 37mV. This allows the device to approximate a wide range of charging lines; it is not limited to constant current or even monotonically decreasing functions. OPERATION Normal Mode Upon application of power, the DS1633 will perform an initialization cycle requiring eight seconds. During this period it will determine if a battery is connected to the battery input by applying a voltage through 5 KΩ output impedance and looking for a non–zero current flow out of the pin. If a battery is connected, the value of the battery voltage will be determined using a 7–bit A/D convertor. This value will be used to determine which of the 32 user–defined breakpoints should be used to set RTH and VOC. Generally, as the battery charges the battery voltage will increase. When the battery voltage reaches or exceeds each user–defined breakpoint, the values of RTH and VOC will be modified accordingly. The battery voltage is measured and adjustments are made every eight seconds. The battery detection is performed at one–second intervals. If the amount of time the battery has been charging exceeds the preset limit, the device will apply the VOC and RTH as before, but only for a fraction of the eight–second cycle time. This duty cycle can be as low as 1/64 or as high as 1. In this way trickle charge can be accomplished by time averaging a short pulse over a longer period. Refer to Figure 2 for a detailed flow diagram of normal operation. PROGRAMMING MODE Register Structure To configure a DS1633 to operate with a unique load line the user must program a set of 25–bit internal registers (Table 1). The first 32 (0–31) of these registers contain the information needed to locate each breakpoint and what the RTH and VOC are at that breakpoint, as well as the duty cycle to be used after the optional timer has expired. The last (32) register contains the bits which 052694 2/11 select the system power supply level (5V or 6V), the timer option, and the time limit (2 to 32 hours in 2–hour increments). BREAKPOINT REGISTER STRUCTURE Break Point Voltage Field The break point voltage field specifies the range of battery voltage over which the RTH, VOC and pulse frequency information contained in that register is valid. This information is valid when the battery voltage meets or exceeds the breakpoint value, but is less than the next breakpoint value: VBPX < VBAT < VBP(x+1) The xth breakpoint voltage (VBPX) is determined according to the following formula: VBPX(n) = (n/127)(4.699V) ; for 0 < n < 127 The value for n is entered in the field as a 7–bit binary value, LSB first. For reliable operation the first (x=0) breakpoint should be programmed such that VBP0 = 0. Successive breakpoints should be programmed with increasing values, that is: VBPX < VBP(x+1) If not all of the available breakpoints are used, the unused points should be assigned the maximum VBP value (n=127) of 4.699V with RTH and VOC set to their maximum values (5060Ω and 5.5V) and the duty cycle field set to its minimum or zero value. OPEN CIRCUIT VOLTAGE FIELD The open circuit voltage field specifies the value of VOC to be applied to the battery. VOC can be set for values between 1.3V and 5.5V. This field is entered as a 7–bit binary value, LSB first. The value of VOC(n) is determined as follows: VOC(n) = 1.3V + n(5.5V – 1.3V)/127 ; for 0 < n < 127 For reliable operation of the battery detection circuitry, the minimum value of VOC should be greater than the maximum battery voltage. DS1633 THEVENIN RESISTANCE FIELD The Thevenin resistance field specifies the value of output resistance between the low impedance VOC source and the battery pin. This resistance can have one of 128 values ranging from 5060Ω to 7.5Ω with a 5% difference in successive values. This field is entered as a 7–bit binary value, LSB first. The value of RTH(n) is determined as follows: RTH(n) = 7.5(0.95n–127) ; for 0 < n < 127 indicates a 5V system and charging will begin when VCC exceeds 4.75V. TIMER STATUS FIELD This is a one bit field which indicates if the timer is to be used. A one in this field indicates that timer is used, a zero that it is not. TIMER VALUE FIELD The pulse width field specifies the amount of time (PW) during each eight second charging and evaluation cycle that VOC and RTH will be applied after the optional timer has expired. PW can have one of 8 values ranging from 8 seconds to 0. The field is entered as a 3–bit binary value, LSB first. The value of PW is determined as follows: This field specifies the maximum time (TMAX) for standard or non–pulsed charging. During the period when the timer has not expired, VOC and RTH will be applied to the battery input if the charge on bit is a one. When the elapsed charge time exceeds the value in this register, VOC and RTH will be applied at a duty cycle determined by the PW field for each breakpoint. The field is entered as a 4–bit binary value, LSB first. The timer can have values from 2 to 32 hours, determined by the following: PW(n) = 2n/16 ; for 1 < n < 7 TMAX(n) = 2(n + 1) ; for 0 < n < 15 PULSE WIDTH FIELD PW(n) = 0 ; for n = 0 CHARGE ON FIELD This is a one bit field which specifies if VOC and RTH for this breakpoint are to be applied at all for the case of an unexpired timer. Its usefulness is in permitting certain breakpoints to be turned off if the battery voltage exceeds a maximum during standard charge. If the timer has expired or is not used, this is accomplished for those breakpoints using the 3 pulse width bits (PW = 000). A one in this field means that the VOC and RTH are to be applied when the breakpoint is the current one. CONFIGURATION REGISTER STRUCTURE VTRIP Field This is a one–bit field which specifies the valid supply voltage for the device. A one in this field indicates a 6V system is being used and the part will not begin charging until the applied VCC exceeds 5.7V. Conversely, a zero PROGRAMMING OPERATION The data for the 33 registers is stored in nonvolatile memory and can be written only once. All 33 registers must be programmed before any can be read. Note that although the configuration register contains only 6 bits, 25 bits are required to be entered; therefore, fill it with 19 0’s. The registers are programmed sequentially, starting at register 0. As each register is programmed, an internal pointer moves to the next register until all 33 have been programmed. To enter the program/read mode, VCC must be taken to 8V for a minimum of 1 ms and returned to 5V. The VBAT pin is now configured to operate as a single wire I/O line. The hardware interface is shown in Figure 3. RESET TIMING To issue a reset to the device the VBAT pin must be brought low and held low for a minimum of 480 µs after which it is released and will return to a high level through the internal pullup resistor. After the line is allowed to return high it must not be pulled low for at least 1 µs. Refer to Figure 4. 052694 3/11 DS1633 WRITE TIMING A logic 0 is written by bringing the VBAT pin low for at least 60 µs, but not more than 120 µs. A logic 1 is written by bringing the VBAT pin low for at least 1 µs, but not more than 15 µs. After the line is allowed to return high it must not be pulled low for at least 60 µs. Refer to Figure 4. READ TIMING A read is performed by bringing the VBAT pin low for at least 1 µs, but not more than 5 µs and then releasing it. A logic 1 is indicated by the pin returning high. The state of the VBAT pin should be sampled at most 15 µs after VBAT is pulled low. A high level indicates a read ‘1’, a low level indicates a read ‘0’. PROGRAMMING To program the DS1633 the single line I/O must be enabled by bringing VCC to 8V for at least 1 ms and then back to 5V. The first register can now be written. The register data must be preceded by 3 consecutive logic 1 write cycles. The register data can now be entered 052694 4/11 according to the write cycle timing detailed above, from LSB to MSB. To commit the data to the nonvolatile memory the VBAT pin is brought to 12V, with VCC at 8V, for at least 250 ms. When VBAT is released and returns to 5V and a reset cycle is issued the device is ready for the next register. Be careful not to issue multiple resets as this will move the pointer. This sequence is repeated until all 33 registers are programmed. When all registers have been programmed, the DS1633 disables the serial interface and begins normal operation. VERIFICATION To verify the data contained in the registers the single line I/O must be enabled by bringing VCC to 8V for at least 1 ms. Unlike the programming operation, the read operation allows random access of the registers. A read cycle is preceded by 4 logic ones, a 6–bit register address, entered LSB first, and 18 logic ones. The device will now output the contents of the register, LSB first, on the next 25 read cycles. To read another register, issue a reset and repeat the sequence. DS1633 SIMPLIFIED BLOCK DIAGRAM Figure 1 OPEN CIRCUIT VOLTAGE (VOC) OUTPUT RESISTANCE (RTH) BANDGAP REFERENCE TO BATTERY PIN 7 7 14 NONVOLATILE MEMORY 7–BIT A/D CONVERTOR DS1633 REGISTER STRUCTURE Table 1 MSB DS1633 MEMORY ARRAY MAP LSB REGISTER CHARGE ON PULSE WIDTH THEVENIN RESISTANCE FIELD OPEN CIRCUIT VOLTAGE BREAKPOINT VOLTAGE 0 CO0 PW0 RTH0 VOC0 VBP0 1 2 3 D D D 30 31 32 CO31 PW31 RTH31 MUST FILL UNUSED BITS WITH 0’S VOC31 VBP31 TIMER VALUE TIMER STATUS VTRIP 052694 5/11 DS1633 DS1633 OPERATION FLOW CHART Figure 2 POWER DOWN NO CHARGING BATTERY BACKUP POWER UP 1/SEC NO TIMER EXPIRED YES YES TIMER BIT SET IN MODE SEL CHARGE ON? RESET TIMER YES SET CHARGE ON DUTY CYCLE WITH PULSE FREQ (2:0) 3 SAMPLES INDICATE NO BATTERY NO YES RUN WITH CURRENT LOAD LINE DATA LAST 512 MSEC OF 8 SECONDS READ EPROM DATA LATCH DATA YES VBAT>VBP NO DECREMENT ADDRESS YES NO ADDRESS 31 052694 6/11 FORCE CHARGE ON, RTH TO 5K 3 SAMPLES OVER 2 MSEC NO SET CHARGE ON WITH PULSE FREQ BIT 3 NO YES 1/SEC FIRST PASS 8 SECOND SETUP TO FIND INITIAL CHARGING POINT NO CHARGE CURRENT STILL IN FIRST PASS NO DS1633 HARDWARE INTERFACE FOR PROGRAMMING Figure 3 12V VCC PROGRAM REGISTER 5K Q D VBAT D Q DS1633 INTERFACE TO PROGRAMMING CIRCUITRY I/O SIGNAL TIMING Figure 4 CYCLE N CYCLE N+1 tTS tREC tREC WRITE 1 VBAT t1 tTS tREC tREC WRITE 0 t0 tTS tREC READ ÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎ tREC DATA VALID VBAT tREAD tSAMPLE tR RESET VBAT ÎÎÎ ÎÎÎ tREC 052694 7/11 DS1633 REGISTER VALUE CROSS REFERENCE Table 2 HEX DEC RTH 00 0 5.060E+03 01 1 4.807E+03 02 2 03 04 VOC VBP HEX DEC RTH VOC VBP 1.30 0.000 26 38 7.205E+02 2.56 1.406 1.33 0.037 27 39 6.845E+02 2.59 1.443 4.567E+03 1.37 0.074 28 40 6.503E+02 2.62 1.480 3 4.338E+03 1.40 0.111 29 41 6.178E+02 2.66 1.517 4 4.122E+03 1.43 0.148 2A 42 5.869E+02 2.69 1.554 05 5 3.915E+03 1.47 0.185 2B 43 5.575E+02 2.72 1.591 06 6 3.720E+03 1.50 0.222 2C 44 5.297E+02 2.76 1.628 07 7 3.534E+03 1.53 0.259 2D 45 5.032E+02 2.79 1.665 08 8 3.357E+03 1.56 0.296 2E 46 4.780E+02 2.82 1.702 09 9 3.189E+03 1.60 0.333 2F 47 4.541E+02 2.85 1.739 0A 10 3.030E+03 1.63 0.370 30 48 4.314E+02 2.89 1.776 0B 11 2.878E+03 1.66 0.407 31 49 4.098E+02 2.92 1.813 0C 12 2.734E+03 1.70 0.444 32 50 3.894E+02 2.95 1.850 0D 13 2.598E+03 1.73 0.481 33 51 3.699E+02 2.99 1.887 0E 14 2.468E+03 1.76 0.518 34 52 3.514E+02 3.02 1.924 0F 15 2.344E+03 1.80 0.555 35 53 3.338E+02 3.05 1.961 10 16 2.227E+03 1.83 0.592 36 54 3.171E+02 3.09 1.998 11 17 2.116E+03 1.86 0.629 37 55 3.013E+02 3.12 2.035 12 18 2.010E+03 1.90 0.666 38 56 2.862E+02 2.15 2.072 13 19 1.909E+03 1.93 0.703 39 57 2.719E+02 3.19 2.109 14 20 1.814E+03 1.96 0.740 3A 58 2.583E+02 3.22 2.146 15 21 1.723E+03 1.99 0.777 3B 59 2.454E+02 3.25 2.183 16 22 1.637E+03 2.03 0.814 3C 60 2.331E+02 3.28 2.220 17 23 1.555E+03 2.06 0.851 3D 61 2.215E+02 3.32 2.257 18 24 1.478E+03 2.09 0.888 3E 62 2.104E+02 3.35 2.294 19 25 1.404E+03 2.13 0.925 3F 63 1.999E+02 3.38 2.331 1A 26 1.333E+03 2.16 0.962 40 64 1.899E+02 3.42 2.368 1B 27 1.267E+03 2.19 0.999 41 65 1.804E+02 3.45 2.405 1C 28 1.203E+03 2.23 1.036 42 66 1.714E+02 3.48 2.442 1D 29 1.143E+03 2.26 1.073 43 67 1.628E+02 3.52 2.479 1E 30 1.086E+03 2.29 1.110 44 68 1.547E+02 3.55 2.516 1F 31 1.032E+03 2.33 1.147 45 69 1.469E+02 3.58 2.553 20 32 9.802E+02 2.36 1.184 46 70 1.396E+02 3.61 2.590 21 33 9.312E+02 2.39 1.221 47 71 1.326E+02 3.65 2.627 22 34 8.846E+02 2.42 1.258 48 72 1.260E+02 3.68 2.664 23 35 8.404E+02 2.46 1.295 49 73 1.197E+02 3.71 2.701 24 36 7.984E+02 2.49 1.332 4A 74 1.137E+02 3.75 2.738 25 37 7.585E+02 2.52 1.369 4B 75 1.080E+02 3.78 2.775 052694 8/11 DS1633 HEX DEC RTH 4C 76 1.026E+02 4D 77 9.747E+01 4E 78 4F 79 50 VOC VBP HEX DEC RTH VOC VBP 3.81 2.812 66 102 2.704E+01 4.67 3.774 3.85 2.849 67 103 2.569E+01 4.71 3.811 9.260E+01 3.88 2.886 68 104 2.440E+01 4.74 3.848 8.797E+01 3.91 2.923 69 105 2.318E+01 4.77 3.885 80 8.357E+01 3.95 2.960 6A 106 2.202E+01 4.81 3.922 51 81 7.939E+01 3.98 2.997 6B 107 2.092E+01 4.84 3.959 52 82 7.542E+01 4.01 3.034 6C 108 1.988E+01 4.87 3.996 53 83 7.165E+01 4.04 3.071 6D 109 1.888E+01 4.90 4.033 54 84 6.807E+01 4.08 3.108 6E 110 1.794E+01 4.94 4.070 55 85 6.467E+01 4.11 3.145 6F 111 1.704E+01 4.97 4.107 56 86 6.143E+01 4.14 3.182 70 112 1.619E+01 5.00 4.144 57 87 5.836E+01 4.18 3.219 71 113 1.538E+01 5.04 4.181 58 88 5.544E+01 4.21 3.256 72 114 1.461E+01 5.07 4.218 59 89 5.267E+01 4.24 3.293 73 115 1.388E+01 5.10 4.255 5A 90 5.004E+01 4.28 3.330 74 116 1.319E+01 5.14 4.292 5B 91 4.753E+01 4.31 3.367 75 117 1.253E+01 5.17 4.329 5C 92 4.516E+01 4.34 3.404 76 118 1.190E+01 5.20 4.366 5D 93 4.290E+01 4.38 3.441 77 119 1.131E+01 5.24 4.403 5E 94 4.076E+01 4.41 3.478 78 120 1.074E+01 5.27 4.440 5F 95 3.873E+01 4.44 3.515 79 121 1.020E+01 5.30 4.477 60 96 3.678E+01 4.47 3.552 7A 122 9.693E+00 5.33 4.514 61 97 3.494E+01 4.51 3.589 7B 123 9.208E+00 5.37 4.551 62 98 3.320E+01 4.54 3.626 7C 124 8.748E+00 5.40 4.588 63 99 3.154E+01 4.57 3.663 7D 125 8.310E+00 5.43 4.625 64 100 2.996E+01 4.61 3.700 7E 126 7.895E+00 5.47 4.662 65 101 2.846E+01 4.64 3.737 7F 127 7.500E+00 5.50 4.699 052694 9/11 DS1633 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -1.0V to +7.0V 0°C to 70°C –55°C to +125°C 260°C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. RECOMMENDED DC OPERATING CONDITIONS PARAMETER (0°C to 70°C) SYMBOL MIN TYP MAX UNITS NOTES VCC1 4.75 5 6.5 V 1,2 6V Mode Supply Voltage, Operation VCC2 5.7 6 6.5 V 1,3,4 Supply Voltage, VBAT, Programming VBATP 12 12 13 V IBAT, Programming IBATP 100 µA VCC Supply Voltage, Programming VCC3 8.5 V 5V Mode Supply Voltage, Operation 8 Logic 1 Input VIH 2.0 – VCC+0.3 V Logic 0 Input VIL –0.3 – +0.8 V MIN TYP MAX UNITS NOTES 1 mA 6 DC ELECTRICAL CHARACTERISTICS PARAMETER Supply Current, Operation Mode SYMBOL (0°C to 70°C; VCC=5.75V) ICC1,2 Supply Current, Programming Mode ICC3 10 mA Output Low, Voltage VOL 0.4 V Output Low, Current IOL VBAT Leakage Current with VCC at 0V IBAT 1 mA 100 Pullup resistance on I/O RPU 5K Breakpoint Voltage (n=0) VBP(0) 0 Breakpoint Voltage (n=127) VBP(127) Open Circuit Voltage (n=0) VOC(0) Open Circuit Voltage (n=127) Thevenin Resistance (n=0) VOC(127) 4.649 4.699 5.45 5.50 4.749 V V 5.55 7.5 V Ω 7 7 Thevenin Resistance (n=127) RTH(127) 4933 5060 5187 Ω Timer Value (n=0) TMAX(0) 1.8 2 2.2 hours Timer Value (n=15) TMAX(127) 28.8 32 35.2 hours 052694 10/11 5 V 1.3 RTH(0) nA DS1633 AC ELECTRICAL CHARACTERISTICS: DATA TRANSMISSION PARAMETERS PARAMETER SYMBOL MIN Reset Active tR 480 Logic 1 Active Low t1 1 15 s Logic 0 Active Low t0 60 120 s Read Enable Time tREAD 1 5 µs 15 µs Time from Read Enable to I/O Line Sampling TYP tSAMPLE MAX UNITS NOTES s Data Transfer Window tTS 60 120 s Active Signal Pulse Width, Data I/O tPW 60 120 s Recovery Time Between Windows tREC 1 µs Programming Pulse Width, VBAT tPRG 250 ms NOTES: 1. All voltages referenced to ground. 2. 5V operation conditions. 3. 6V operation conditions. 4. For any VOCMAX > 4.5V, VTRIP = 5.7V (6V operation) must be used. 5. High impedance isolation between VBAT and VCC with VCC=0 is > 45GΩ. 6. Does not include current supplied to the battery pin. 7. At 25°C, RTH has a positive temperature coefficient of approximately 800 ppm/°C. 052694 11/11 APPLICATION NOTE 54 Application Note 54 Increasing Charging Current and Voltage for the DS1633 Battery Recharger INTRODUCTION The DS1633 Battery Recharger is designed to be a complete battery charging system for standard charge or trickle charge applications. The device is flexible enough to be used with a variety of battery chemistries and cell capacities. It provides timer termination of standard charge and automatically shifts into trickle charge. Battery voltage may be monitored and charging terminated if it exceeds a preset maximum as a safety feature. The output load line may be specified as the usual constant current recharge with a voltage limit or it may be configured to approximate any practical load line. All parameters, such as power supply range, charge current load line, trickle charge rate, and timer setting, are programmed into nonvolatile memory using the battery pin as a one–wire communication port. This functionality is provided in a small, 3–pin TO–220 package. The DS1633’s functionality is a result of its unique architecture. The device monitors the battery voltage and adjusts the values of the output impedance (RTH) and the open circuit voltage (VOC) it presents to the battery. These values may be adjusted at 32 user–definable points (breakpoints) that occur roughly every 37 mV. This allows the device to approximate a wide range of charging lines and is not limited to constant current or even monotonically decreasing functions. Using only the DS1633, supply voltages of either 5V or 6V may be used, and battery voltages as high as 4.7V (3.7V for 5V supplies) are allowed. The DS1633 is available in preprogrammed versions, with charging currents up to 100 mA available. These provide for a simple component solution to several battery charging tasks, which users may stock and use when needed. For typical NiCd batteries, the 4.7V limit on battery voltage limits the battery stack to three cells. Many battery packs today use five cells. In addition, with higher capacity battery packs available, there are situations which require charging currents higher than 100 mA. This application note examines some circuit alternatives that allow the DS1633 to be used with battery packs that have more than three cells, or in applications which require higher charging currents. Other circuit features are presented which show how easily the DS1633 can be made into a full–featured charging system. DEFINITIONS The DS1633 has only three pins, as shown in Figure 1. The voltages which will be referred to throughout this application note are defined in Figure 1 and in the table below. VOLTAGE DESCRIPTION LIMITS VCC DS1633 Supply Voltage 5V mode: 4.75V<VCC<6.5V referred to VGND 6V mode: 5.7V<VCC<6.5V referred to VGND VBAT Battery Voltage 5V mode: 0<VBAT<3.7V referred to VGND 6V mode: 0<VBAT<4.7V referred to VGND VGND Ground. All DS1633 voltages are referred to this potential. None Copyright 1995 by Dallas Semiconductor Corporation. All Rights Reserved. For important information regarding patents and other intellectual property rights, please refer to Dallas Semiconductor databooks. 020193 1/7 APPLICATION NOTE 54 DS1633 VOLTAGE DEFINITIONS Figure 1 1 3 DS1633 2 VCC VGND VBAT OV ADDING A CHARGE INDICATION LED Figure 2 V+ RSENSE 1 2N2907 DS1633 3 2 RLED 1K R SENSE 020193 2/7 0.7V I CHG APPLICATION NOTE 54 ADDING AN LED FOR CHARGING INDICATION Typically, battery chargers have some visual indication that standard charging is taking place and may also indicate trickle charge mode. This feature is easy to add to a DS1633, using the circuit shown in Figure 2. The DS1633 draws only 1 mA of quiescent current itself. The sense resistor, RSENSE, is selected so that when the charging current begins to be drawn from the V+ supply, 0.7V is dropped across it. This forward–biases the transistor, allowing current to flow out of the transistor’s collector to drive the LED. The LED current is limited by RLED. The values for RSENSE and RLED depend upon the charger application. To turn on the transistor, the voltage drop across RSENSE must be greater than 0.7V. The value for RSENSE may be found by where ICHG is the magnitude of the charging current. The 1K resistor to ground is optional; it may be needed to set a proper operating point for the transistor to switch properly when the DS1633 is in trickle mode. It is important to note that the voltage drop across RSENSE must be accounted for in the overall charger design; the DS1633’s VCC limits must be observed. For example, with a DS1633 in 6V mode, and a charge current of 50 mA, RSENSE would be 14 ohms; a 15 ohm resistor would do fine as the closest available 10% resistor value. This means that 0.75V would be dropped across RSENSE; and so V+ must be in the range 6.45V<V+<6.5V, so that the DS1633’s VCC limits are met. The upper limit is not changed by the addition of the resistor, since when the DS1633 goes into trickle mode, the output current will at times drop to zero, so only the quiescent current of the DS1633 is flowing. This would cause the full input voltage to be seen at pin 1. A regulated V+ is therefore necessary. The value for RLED depends upon the type of LED used, and its desired brightness. Typically, LEDs drop approximately 2V across them, and require 20 mA of drive current for full brightness. Using this information, and assuming that the VCESAT of the 2N2907 is negligible, RLED may be found by R LED + For example, using a V+ of 7V as found above, RLED would be 250 ohms for full brightness; a 510 ohm resistor could be used for a slightly dimmer LED. Some LEDs can be driven with as little as 1 or 2 mA; use the lowest current possible to drive the LED in order to reduce the current drive requirements of the power supply for the charger. One of the interesting aspects of this circuit is its operation in trickle mode. In standard charge mode, the LED will be on all the time. When the DS1633 moves into trickle mode, however, it does so by pulsing the standard charge current at some specified duty cycle. This means that trickle mode will be indicated by the LED blinking at a slow rate. When full charge is achieved, (i.e. the battery voltage limits have been met), current is turned off completely, and the LED will be extinguished. Thus, this indicator can show when the DS1633 is in standard charge mode, in trickle charge mode, and when charging is complete. INCREASING OUTPUT CURRENT While the DS1633 is capable of supplying up to 100 mA of charging current, there are situations where more charging current is desired. For example, an 800 mAh battery pack would require almost 13 hours of charging at 100 mA. If the charging current could be increased to 160 mA, this battery could be fully charged in 8 hours. Preprogrammed DS1633’s come in several different charge currents, all with 8 hour timer cutoff. The products that are available preprogrammed, requiring no further programming by the user, are shown in Table 1. PRODUCT SELECTION GUIDE Table 1 PART NUMBER IMAX (mA) VMAX (V) TIMER (Hours) DS1633–A 100 4.65 8 DS1633–B 80 4.65 8 DS1633–C 60 4.65 8 DS1633–D 40 4.65 8 DS1633–E 20 4.65 8 (V )) * 2V 20 mA 020193 3/7 APPLICATION NOTE 54 Since the DS1633 is essentially a voltage source with an adjustable resistor, it is capable only of sourcing current; it cannot sink current. This fact makes it possible to place any number of DS1633’s in parallel, with no need for any external components. It is generally wise, however, to keep the timer lengths of the paralleled parts the same to avoid one going into trickle much before its counterpart does. Using this approach, the 800 mAh battery may be charged using a charger as shown in Figure 3. PARALLEL DS1633’s Figure 3 1 DS1633–B 3 2 1 DS1633–B 3 2 The charge indication circuit of Figure 2 may be used with this circuit to provide an indication of charging status. INCREASING BATTERY VOLTAGE RANGE The battery voltage limits on the DS1633 are suitable for NiCd battery packs with up to three cells. With five cell battery packs increasing in usage, a method of charging these battery packs using the DS1633 is desirable. Since the limit on the battery voltage is 4.7V referred to VGND, it is possible to raise the potential of VGND to keep VBAT within limits. This method allows the DS1633 to charge any number of NiCd cells, with certain constraints. 020193 4/7 The circuit of Figure 4 provides the DS1633 with the ability to charge a five cell NiCd battery pack. Typically, a NiCd cell will be considered fully discharged when the cell voltage goes to 0.9V. This means the total voltage across the battery pack at a minimum will be 4.5V. By offsetting the DS1633 GND pin to 4.3V using the zener diode shown, the VBAT referred to ground will range from 0.2V (when the battery potential is 4.5V) to 3.7V (when the battery potential is 8V, in a fully charged condition). Note that by offsetting the GND pin, the V+ voltage required for the DS1633 is now between 10V and 11.5V (these levels keep VCC between 5.7V and 6.5V referred to VGND). APPLICATION NOTE 54 INCREASING BATTERY VOLTAGE RANGE Figure 4 1 V+ 1N4736 6.8V DS1633 2 VGND 3 5 NiCd Cells 180 1N4731 4.3V 0.022 µF It is possible that the V+ potential may rise faster than the VGND potential from the zener upon power up. If this should happen, the DS1633 may be damaged, or may be placed in a test/programming mode. The 6.8V zener from VCC to VGND assures that this will never happen. The circuit of Figure 4 will work reliably as long as it is never connected to a battery pack which is discharged below 4.5V. Should the VBAT potential ever fall below that of VGND, substrate diodes will be forward biased and large currents will flow; these may damage the DS1633. Therefore, it is advised that this circuit be used with caution, and only if the battery potentials are well known and controlled. A circuit which allows battery voltages to go below 4.5V and still will charge batteries with more than three cells is shown in Figure 5. This circuit has several features which will be discussed below. The first feature of this circuit consists of Q1, R2, and D1; this simple pass voltage regulator supplies the DS1633 with VCC of 6.2V referred to VGND at all times. This serves two purposes, the first of which is to allow the V+ supply for the charger to be a convenient value, such as +12V, rather than requiring a precise 10V or 11V, as with the circuit in Figure 4. The second purpose will become clear in a moment. 020193 5/7 APPLICATION NOTE 54 BATTERY CHARGER FOR ONE TO FIVE CELLS Figure 5 Q1 2N2222 +12V 1 DS1633 1K R1 180 R2 3 2 D1 1N4736 6.8V R3 10K 3 1K D2 1N4731 4.3V Q2 2N2907 R1 and D2 set up the offset ground reference voltage, as was done in the circuit of Figure 4. The reference voltage is connected to VGND through Q2, which is configured as an emitter follower. Note that this will place VGND at approximately 0.7V above the zener voltage of D2. The reference voltage is also fed to a comparator, consisting of U1 and R3. The comparator compares the battery voltage with the reference supplied by R1 and D2. If the battery voltage is below 4.3V, the comparator’s output will go high. This will turn on Q3, which will effectively pull VGND down to within a few millivolts of the ground potential. This is good enough to make the DS1633 operate at battery voltages between 0V and 4.3V. 020193 6/7 7 Q3 2N2222 R4 – + 2 U1 LM311 If the battery voltage is above 4.3V, Q3 is turned off, and VGND goes to the reference voltage as supplied through Q2. The change in ground reference voltage is automatic, and will occur during charging if necessary. It is this ability to dynamically shift the VGND potential which requires the regulator circuit initially discussed. This regulator “floats” with the VGND voltage, and will maintain the proper VCC voltage for the charger for either VGND potential available. A full–featured charger which provides this automatic battery voltage sensing and charge indication is shown in Figure 6. APPLICATION NOTE 54 FULL FEATURED BATTERY CHARGER Figure 6 +12V 15 2N2222 1 2N2907 DS1633 1K 3 2 1N4736 6.8V 180 10K 3 1K 5.6K 2N2907 7 2N2222 – + 1N4731 4.3V 2 LM311 Another method of charging batteries with more than three cells is an alternative to the method presented above. Instead of offsetting the DS1633’s VGND, it is possible to change the battery’s reference point. This is accomplished by using a bipolar supply to drive the DS1633. The positive side drives the DS1633, while the negative supply is used as the battery reference, as shown in Figure 7. As with the circuit of Figure 4, this approach works well provided that the battery voltage is greater than 5V at all times. Other negative potentials may be used to adjust the circuit to a specific application. USING A BIPOLAR SUPPLY TO INCREASE BATTERY VOLTAGE RANGE Figure 7 +5V BIPOLAR POWER SUPPLY GND 1 DS1633 2 3 5 NiCd CELLS –5V 020193 7/7