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DS2714
Quad Loose Cell NiMH Charger
www.maxim-ic.com
GENERAL DESCRIPTION
The DS2714 is ideal for standalone charging of 1 to 4 AA or AAA NiMH "loose" cells. NiCd cells can also be charged. Temperature, voltage and charge time are monitored to provide proper fast charging control algorithms for Nickel Metal Hydride (NiMH) batteries. Battery tests are included to detect defective or inappropriate cells such as Alkaline primary batteries. The DS2714 supports a parallel charging topology, with independent monitoring and control of each cell.
FEATURES
Charges 1 to 4 NiMH Cells Detects and Avoids Charging Alkaline Cells Pre-Charges Deeply Depleted Cells Fast Charges NiMH with -V Termination Sensitivity of 2mV (typ) Monitors Voltage, Temperature and Time for Safety and Secondary Termination Works with Regulated Charge Current Source Drives PNP Type Pass Element Compatible with Integrated Primary-Side PWM Controllers 20-pin TSSOP Package
APPLICATIONS
Desktop/Standalone Chargers (AAA/AA) Digital Still Cameras Music Players Games Toys
ORDERING INFORMATION
PART DS2714E+ DS2714E+T&R MARKING DS2714 DS2714 PIN-PACKAGE 20 TSSOP 20 TSSOP Tape-and-Reel
+Denotes lead-free package.
CHARGE TOPOLOGY
PIN CONFIGURATION
TSSOP
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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REV: 080206
DS2714: Quad Loose Cell NiMH Charger
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to VSS Voltage on DMSEL Continuous Sink Current CC1-4, LED1-4 Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +6V VDD + 0.3V 20mA -40°C to +85°C -55°C to +125°C See IPC/JEDECJ-STD-020A
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 the absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CONDITIONS
(4.0V VDD 5.5V; TA = -20°C to +70°C) PARAMETER Supply Voltage Input Voltage Range SYMBOL VDD CONDITIONS (Note 1) LEDx, DMSEL MIN 4.0 -0.3 TYP MAX 5.5 5.5 UNITS V V
DC ELECTRICAL CHARACTERISTICS
PARAMETER Supply Current, VDD Output Voltage Low, CC1-4. LED1-4 Leakage Current, CC1-4 LED1-4 Threshold Voltage, -V Termination Mode Test Current, DMSEL Input Logic High, DMSEL, Input Logic Low, DMSEL, Input Leakage Current, DMSEL Threshold Voltage, Cell Test Accuracy Threshold Voltage, Cell Test Range Threshold Voltage, Cell Voltage Low Threshold Voltage, Cell Voltage Max1 Threshold Voltage, Cell Voltage Max2 Threshold Voltage, Thermistor - Min Threshold Voltage, Thermistor - Max Threshold Voltage, Thermistor - Stop Threshold Current, TMR Pin Suspend SYMBOL IDD VOL1 ILKG V-V IMTST VIH VIL IIL1 VCTST-ACC VCTST-RANGE VBAT-LOW VBAT-MAX1 VBAT-MAX2 VTHM-MIN VTHM-MAX VTHM-STOP ITMR-SUS
(4.0V VDD 5.5V; TA = -20°C to +70°C. Unless otherwise noted.) CONDITIONS Operating mode VDD = 5.0V, IOL = 20mA (Note 1) VDD = 5.0V, Output inactive After tTHO Pulse high/low once <5ms after power-up (Note 1) (Note 1) After power-up mode select, DMSEL = VDD or VSS RTMR = 80K MIN TYP 500 MAX 750 1.0 -1 1.0 VDD 0.2V 0.2 -1 -15 32 CC1 = CC2 = hi-Z (Note 1, 2) CC1 = CC2 = hi-Z (Note 1, 2) CC1, CC2 active (Note 1, 2) (Note 1, 2, 6) (Note 1, 2, 6) (Note 1, 2, 6) 0.30 0.9 1.55 1.64 1.0 1.65 1.75 VDD x 0.73 VDD x 0.33 VDD x 0.29 0.1 +1 15 400 1.1 1.75 1.86 2.0 5 +1 3.0 15 UNITS A V A mV A V V A % mV V V V V 0.36 V V 0.5 A
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DS2714: Quad Loose Cell NiMH Charger PARAMETER Presence Test Current, VP1-4 Reverse Leakage Current, VP1, VP2, VP3, VP4 SYMBOL IPTST ILKGR CONDITIONS VDD = 0V, VPx = 1.5V MIN TYP 10 MAX 15 2 UNITS A A
ELECTRICAL CHARACTERISTICS: TIMING
Internal Timebase Period Internal Timebase Accuracy Duty Factor, Fast Charge Duty Factor, PreCharge/Top-Off Duty Factor, Maintenance Charge Cell Test Interval Pre-Charge Time-out Fast Charge Termination Hold-Off Period Fast Charge Flat Voltage Time-out Charge Timer Accuracy Charge Timer Range
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7:
(4.0V VDD 5.5V; TA = -20°C to +70°C. Unless otherwise noted.) PARAMETER SYMBOL CONDITIONS tBASE (Note 5)
MIN
TYP 0.48
MAX
UNITS s
-10 DF1 DF2 DF3 tCTST tPCHG tTHO tFLAT VCELL not increasing CCx CCx CCx Note 4 (Note 3) VCELL < VBAT-MIN 30.6 3.6 14.4 -5 tCTMR-RANGE 0.5 0.234 0.0625 0.0078 31 34 4 16
+10
%
s 37.4 4.4 17.6 +5 10 minutes minutes minutes % h
Voltages relative to VSS. Specification applicable during charge cycle with TA = 0°C to +70°C. One time slot out of every 16 available slots gets a Cell Test. One time slot out of every 32 available time slots gets a charge pulse. 0.48 seconds is one charge time slot. A complete cycle of 4 time slots (one charge time slot per cell) is 1.92 sec. VTHM-MIN, VTHM-MAX, and VTHM-STOP are fixed ratios of VDD. Their ranges never overlap. IMTST current is applied as a source current and as a sink current within 5ms after power-up.
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DS2714: Quad Loose Cell NiMH Charger
PIN DESCRIPTION
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 NAME CC1 CC2 CC3 CC4 LED1 LED2 VSS LED3 LED4 DMSEL CTST TMR VDD VSS VP1 VP2 VP3 VP4 THM1 THM2 FUNCTION Charge Control 1. Turn on and off the charge PNP for Cell 1. Charge Control 2. Turn on and off the charge PNP for Cell 2. Charge Control 3. Turn on and off the charge PNP for Cell 3. Charge Control 4. Turn on and off the charge PNP for Cell 4. LED 1. Open drain output for LED. Display Cell 1 status. LED 2. Open drain output for LED. Display Cell 2 status. Device Ground. Return current path for LEDx pins. Both VSS pins must be connected to ground. LED 3. Open drain output for LED. Display Cell 3 status. LED 4. Open drain output for LED. Display Cell 4 status. Display Mode Select. Select the LED blink rate. Cell Test Resistor. Cell test threshold set. Timer Resistor. Charge timer set. Power-Supply Input. Chip supply input (4.0V to 5.5V). Device Ground. Internally connected to Pin 7. Both VSS pins must be connected to ground. Voltage Sense 1. Positive terminal sense input for Cell 1. Voltage Sense 2. Positive terminal sense input for Cell 2. Voltage Sense 3. Positive terminal sense input for Cell 3. Voltage Sense 4. Positive terminal sense input for Cell 4. Thermister 1. Thermister input for Cell 1 and 2. Thermister 2. Thermister input for Cell 3 and 4.
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DS2714: Quad Loose Cell NiMH Charger
Figure 1. Block Diagram
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DS2714: Quad Loose Cell NiMH Charger
Figure 2. State Diagram
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DS2714: Quad Loose Cell NiMH Charger
Figure 3. Application Example: Regulated Current Source Charger
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DS2714: Quad Loose Cell NiMH Charger
DETAILED DESCRIPTION
CHARGE ALGORITHM OVERVIEW
A charge cycle begins in one of three ways: With the application of power to the DS2714 with cell(s) already inserted, with the detection of cell insertion after power-up, or when exiting suspend mode with cell(s) inserted. The charge cycle begins with Pre-charge qualification to prevent Fast charging of deeply depleted cells or charging under extreme temperature conditions. Pre-charging is performed at a reduced rate until the cell being charged reaches VBAT-LOW (1V). The algorithm proceeds to a Fast charge phase which includes cell tests to avoid accidental charging of alkaline cells or NiMH cells which are worn-out or damaged. Fast charging continues as long as the cell temperature is less than 50°C (based on Thermistor sensors THM 1, 2), the open circuit cell voltage(s) are between VBAT-LOW (1.0V) and VBAT-MAX1 (1.65V) and the closed ciruit cell voltage(s) are less than VBAT-MAX2 (1.75V). Fast charging terminates by the -V (negative delta voltage) or flat voltage method. The Top-Off charge phase follows to completely charge the cell. After the Top-off charge timer expires, the Maintenance charge phase continues indefinitely to keep the cells fully charged. Maximum voltage, temperature and charge time monitoring during all charge phases act as secondary or safety termination methods to provide additional protection from overcharge. A cell voltage greater than VBAT-MAX2 (1.75V) will result in a fault condition, and temperature greater than 50°C (see Table 1) will result in either Fault or Maintenance depending on which charge state the device was last in. Each cell is monitored independently, and the charge phase of each cell is independently controlled. If a cell is removed while being charged, the algorithm for that cell slot is completely reset to its Presence Test state without affecting the charge control states of the other cells.
CHARGE CONFIGURATION
The DS2714 supports four slot standalone chargers. It alternates charge to the four slots every two seconds, with one half second available to each cell. Removal or insertion of a cell into the charger does not disturb the charge timing or charge rates of the other cells. Charge pulses are fed alternately to each cell under the control of the CCx pins so that the charge regimes occur in parallel. The duty cycle on the CCx pins are completely independent of one another. Transitions from Pre-charge to Fast charge, Fast charge to Top-off and Top-off to Maintenance occur independently for each cell. The configuration shown in Figure 3 is for charging four cells with a current limited source of 2A. The effective average fast charge current for each cell is 2A x 0.25 x 15/16 = 0.469A. The 15/16 term is due to the fact that every 16th charge time slot is used for negative delta-voltage and impedance testing. No current is delivered to the cell during that time. Mechanical design of the holders is required to prevent insertion of more than one cell in each slot. The holder design should also prevent electrical contact with reverse polarity insertion.
PERFORMANCE REQUIREMENTS OVER TEMPERATURE AND VOLTAGE
Valid NiMH Charge Range Below Operating Voltage Range Low Temperature Range High Temperature Range
Abs. Max Operating Range
INTERNAL OSCILLATORS AND CLOCK GENERATION
An internal oscillator provides the main clock source used to generate timing signals for internal chip operation. The pre-charge timer, hold-off timers, and duty factors for the charging operations are derived from this timebase. There are two separate timers for the impedance test and Fast Charge/Topoff functions.
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DS2714: Quad Loose Cell NiMH Charger
CHARGE TIMER
The Charge Timer monitors the duration of charge in Fast and Top-Off charge phases, and is reset at the beginning of each phase. The time-out period is set with an external resistor connected from the TMR pin to VSS. Resistors can be selected to support Fast charge time-out periods of 0.5 to 10 hours and Top-off charge time-out periods of 0.25 to 5 hours. If the timer expires in Fast charge, the timer count is reset and charging proceeds to the Top-Off charge phase. The Top-Off time-out period is half of the Fast charge time-out period. When the timer expires in Top-Off, charging proceeds to the Maintenance phase. The programmed charge time approximately follows the equation: t = 1.5 * R / 1000 (time in minutes)
SUSPEND
Suspension of charge activity is possible by floating the TMR pin. All CCx outputs become high-Z and the Charge Timer stops. The state machine and all timers are reset to their Presence Test conditions.
TEMPERATURE SENSE
Connecting an external 10k NTC thermistor between THM1 or THM2 (THMx) and VSS, and a 10k bias resistor between VDD and THMx allows the DS2714 to sense temperature. In order to sense the temperature of the battery cells, locate the thermistor close to the body of the battery cell. The THM1 thermistor should be placed between cells 1 and 2, and THM2 thermistor between cells 3 and 4. Alternatively, the thermistors can sense ambient temperature by locating them away from the cells. THM1 and THM2 can be tied together to sense temperature using a single thermistor and bias resistor. The temperature qualification function can be defeated by tying THMx pins to a single resistor divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold voltages. The voltage thresholds of the THMx inputs (VTHM-MIN, VTHM-MAX) are set to allow Fast charging to start if 0°C < TA < 45°C when using the recommended 10k bias and 10k thermistor. If Fast charging is in progress, and the voltage on THMx reaches VTHM-STOP (TA > 50°C), Fast charging stops and the maintenance phase begins. In Precharge the device will transition to the Fault state if the voltage on THMx reaches VTHM-STOP.
MIN, MAX TEMPERATURE COMPARE
Table 1. THM1, THM2 Thresholds
TEMPERATURE THM THRESHOLD
MIN MAX STOP
RATIO OF VDD
0.73 0.33 0.29
THERMISTOR RESISTANCE
27.04k 4.925k 4.085k
Semitec 103AT-2
0°C 45°C 50°C
Fenwal 197-103LAG-A01 173-103LAF-301
4°C 42°C 47°C
CELL VOLTAGE MONITORING
Individual cell voltages are monitored for minimum and maximum values, using the VBAT-LOW, VBAT-MAX1 and VBATthreshold limits. Upon inserting a cell or power-up with cells inserted, cell voltages must be less than the VBATMAX1 threshold before charging begins. The VBAT-LOW threshold determines whether a Pre-charge cycle should precede the Fast charge cycle, and when to transition from Pre-charge to Fast charge. Once Fast charging commences, cell voltages are compared to the VBAT-MAX2 threshold once every 2 seconds. The comparison occurs while the charge control pin (CC1-4) controlling current to the cell is active (low). When the charge control pin is active such that charge is applied to the cell, the cell voltage is referred to as the VON voltage. When the charge control pin is inactive, the cell voltage is referred to as the VOFF voltage. Charging is halted and a Fault condition is displayed if VON is greater than VBAT-MAX2. Charging is also halted and a fault condition is entered if VOFF is greater than VBAT-MAX1. While Fast charge is in progress, cell voltage measurements are stored and compared to future measurements for charge termination and cell test purposes.
MAX2
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DS2714: Quad Loose Cell NiMH Charger
CELL TESTS
Two types of tests are performed to detect primary Alkaline and Lithium cells or defective NiMH or NiCd secondary cells. The first test checks the absolute closed circuit cell voltage (VON), and the second test checks the difference in open circuit cell voltage (VOFF) and (VON). VON for each cell is compared to the VBAT-MAX2 threshold once every 2 seconds. During fast charge, VON - VOFF of each cell is compared to the cell test threshold, VCTST. If VON - VOFF > VCTST, the cell test fails. Cells are tested individually so that a single improper or defective cell can be detected quickly. VCTST is set by the resistance from the CTST pin to ground. The nominal sensitivity of 100mV is set by connecting an 80k resistor between CTST and VSS. The impedance threshold can be set from 32mV to 400mV. The following formula approximates the setting for the impedance threshold VCTST = 8000/R (value in volts)
-V AND FLAT VOLTAGE TERMINATION
During Fast charge, -V detection is performed by comparing successive voltage measurements for a drop of 2mV in the cell voltage. A Hold-off period for -V detection begins at the start of Fast charging and prevents false termination in the first few minutes of the charge cycle. Once the hold-off period expires, cell voltage measurements are acquired every 16th charge time slot (approximately 31 seconds, during the CCx off time). When a newly acquired voltage measurement is greater than any previous one, the new value is retained as the maximum value. When the cell voltage no longer increases, the maximum value is retained and compared against subsequent values. If the cell voltage drops below the -V threshold, V-V, (2mV typ), Fast charging is terminated. If the cell voltage remains flat such that the maximum value persists for a period of 16 minutes (tFLAT), Fast charge terminates and Top-Off charging begins.
TOP-OFF, PRE-CHARGE AND MAINTENANCE
In Top-off and Pre-charge modes, the charger scales the cell current to 1/16 of the DC current set by the current source, i.e, one charge pulse for every 16 main clock pulses, or one in four available time slots for a given cell. The ratio of average Top-off/Pre-charge current to average fast charge current is 0.286. When the charge timer expires in Top-Off, the charger enters Maintenance and delivers 1/128 of the DC charge source current to the cells (one time slot in every 32 available to that cell). This is slightly more than 3% of the average DC Fast Charge current. Maintenance charge remains continuous until power is removed, the cell(s) are removed or the DS2714 is cycled into and out of suspend mode by floating the TMR pin.
CCx OUTPUTS
The CC1 through CC4 pins operate as open-drain outputs that drive active low to connect the charge source to the NiMH cells. During charge, the behavior of these outputs depends on the charge states of the cells and on how many cells have been installed.
FAST CHARGE
Referring to the application circuit shown in Figure 3, CC1 controls the PNP switch that gates current to the cell in slot 1. CC2 controls the PNP switch that gates current to the cell in slot 2, and so on. During Fast charge, current is gated to each slot sequentially, with charge pulses occurring in alternating time frames. The cell in one slot charges while the others relax. Each cell skips a charge pulse every 16 of its allocated charge time slots (approximately once every 31 seconds) to facilitate independent testing of the open and closed circuit cell voltages (VOFF and VON, respectively). Since the charge regime of each cell is independent, one cell may complete a charge phase before the other without affecting the charging of the other cells. In the case of an improper or faulty cell (ex. alkaline) being inserted along with proper cells (NiMH or NiCd), charging of the improper cell would be stopped, while the proper cells will be charged to full.
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DS2714: Quad Loose Cell NiMH Charger
EXAMPLE TIMING DIAGRAM FOR THE DS2714
Note 1: Cell test time slot for Cell 2. Note 2: Cell test time slot for Cell 3.
In this timing diagram, the pulses represent charge current into the individual cells. Cell 1 is in Precharge (the timing of Precharge is the same as Top-off). It gets one charge pulse out of every four available times slots. Cell 2 is in initially in Fast Charge and it transitions to Topoff charge during the N+7th time interval (Note 1)shown in the diagram. Cell 3 is in Fast charge. Cell testing is performed during the interval marked Note 2. This cell is not ready to go into Top-off and it resumes Fast charge. Cell 4 is in maintenance mode, one out of every 32 available time slots gets a charge pulse.
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DS2714: Quad Loose Cell NiMH Charger
LEDx OUTPUTS, DISPLAY MODE SELECT
Open-drain outputs LEDx pull low to indicate charge status. When inactive, the outputs are high impedance. LED1 displays the status for the cell monitored by VP1, LED2 displays the status for the cell monitored by VP2 and so on. The LED pins drive low in three "blink" patterns to annunciate the charge status. Table 2 summarizes the LED operation in each display mode (DM0, DM1, DM2) for each charge condition.
Table 2. Display Patterns By Display Mode and Charge Activity
Display Mode DMSEL pin DM0 DM1 DM2
Low
Charge Activity No Battery
Hi-Z
Pre/Fast/Top-off Charging
Low
Maintenance
0.80s Low 0.16s Hi-Z Hi-Z
Fault
0.48s Low 0.48s Hi-Z 0.16s Low 0.16s Hi-Z 0.16s Low 0.16s Hi-Z
Float
Hi-Z
Low 0.80s Low 0.16s Hi-Z
High
Hi-Z
Low
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.)
Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2006 Maxim Integrated Products · Printed USA
The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.
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