DS2715 DALLAS | Alldatasheet
Document overview
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Technical content
DESCRIPTION
The DS2715 is well suited for cost-sensitive charger applications where the battery is either internal or in a unique battery pack. It has been optimized for safe reliable charging of 1 to10 NiMH cells in series. The DS2715 has an internal gain block that can be selected as either a comparator or transconductance amplifier for charge current regulation. The DS2715 is configurable as a switched DC charger, a linear current regulator, or a switchmode current source. The DS2715 pre-conditions severely depleted cells are pre-conditioned before entering full charge mode. The DS2715 terminates full charge using the dT/dt technique. It requires an external thermistor for dT/dt detection. Over-temperature, under-temperature, and over-voltage detection prevents charging under unsafe environmental conditions. A user selectable charge timer allows charge rates from 0.15C to 2C. Fast-charge, top-off and charge done modes are included for highly reliable, safe charging of NiMH cells. Discharge mode allows the DS2715 to enter a low power sleep state while the cell pack is being discharged.
FEATURES
/g167/g32Charges 1 to 10 NiMH Cells /g167/g32Fast Charges up to a 2C Rate /g167/g32Pre-Charge and Top-Off Charge Modes Help Cell Conditioning /g167/g32Load Detection Allows the DS2715 to Enter Low Power Sleep Mode (Less than 10µA) while the Cell Pack is Discharged /g167/g32dT/dt Charge Termination Eliminates Cell Charge Stress /g167/g32Monitors Voltage, Temperature, and Time for Safety and Secondary Termination /g167/g32Regulates Current through Either Linear Control or Switch-Mode Control /g167/g32LED Outputs Display Charge State /g167/g32Small 16-Pin SO Package
APPLICATIONS
Table 1.
ORDERING INFORMATION
+ Denotes lead-free package. OPERATIONAL DIAGRAM Vch Vbatt THM + - Vdd Sense DS2715 CHARGE SOURCE /LOAD GROUND Divide by n n Cells PART MARKING PIN-PACKAGE DS2715Z+ DS2715+ 16 SO DS2715Z+T&R DS2715+ 16 SO Tape-and-Reel DS2715 NiMH Battery Pack Charge Controller www.maxim-ic.com See Table 1 for Ordering Information. 16 SO CBIAS VCH VSS LED1 LED2 VSS CTG CTG VBATT THM R T VDD SNS- SNS+ DIV MODE 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.
DS2715: NiMH Cell Pack Charge Controller 2 of 12 ABSOLUTE MAXIMUM RATINGS* Voltage on VDD and VCH Pins with Respect to VSS -0.3V to +18V Voltage on LED1 and LED2 Pins -0.3V to +18V Voltage on SNS- -0.3V to +0.3V Voltage on C BIAS -0.3V to 6V Voltage on all Other Pins -0.3V to V Cbias Continuous Sink Current VCH, LED1, and LED2 28mA Operating Temperature Range -20°C to +85°C Storage Temperature Range -55°C to +125°C Soldering Temperature See IPC/JEDECJ-STD-020 *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 (4.5V /g163 VDD /g163 16.5V; TA = 0/g176C to +70/g176C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage V DD (Note 1) 4.5 16.5 V LED1, LED2 Voltage V LED (Note 1) 0.0 16.5 V Mode Voltage V MODE (Note 1) 0.0 V Cbias V VCH Voltage V VCH (Note 1) 0.0 16.5 V CBIAS Capacitor Range C Cbias .02 .15 µF RT Resistor Range R Rt 20 240 K Ω DC ELECTRICAL CHARACTERISTICS (4.5V /g163 VDD /g163 16.5V, TA = 0/g176C to +70/g176C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Linear Mode, VDD = 16.5V 1.3 1.6 mA Operating Current (Note 2) IDDA Comparator Mode, VDD = 16.5V 150 250 µA Idle Current I DDS V DD < VUVLO 10 µA Discharge Current I DDD Discharge latch set (Note 2) 200 µA UVLO Threshold V UVLO V DD Rising (Note 3) 3.8 3.9 4.0 V UVLO Hysteresis V UVLO-HYS V DD Falling 35 mV VCH Sink Current I OL-Vch V OL = 1.5V 20 mA LED1, LED2 Sink Current I OL-LED V OL = 1.0V 20 mA Leakage Current, VCH, LED1, LED2 ILKG Pin inactive or Device Idle -1 +1 µA THM Pin Leakage Current ILKG-THM -1 +1 µA VBATT Pin Leakage Current ILKG-Vbatt -50 +50 nA CBIAS Voltage V Cbias 0 < I Cbias < 0.4ma 3.9 4.0 4.3 V DIV Pin Load Current I Div 500 uA Current Sense Amplifier Gain GERR 100 µA < I Vch < 20mA 5 6.25 7.5 Ω-1 Current Sense Comparator Gain GCOMP (Note 7) 10 Ω-1
DS2715: NiMH Cell Pack Charge Controller 3 of 12 AC ELECTRICAL CHARACTERISTICS (4.5V /g163 VDD /g163 16.5V, TA = 0/g176C to +70/g176C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS UVLO Debounce Time t UVLO 10 µs Current Sense Comparator Propagation Delay tCOMP (Note 7) 250 ns Discharge Detect Propagation Delay tDD From detection of current reversal 1 µs Return To Normal Function (Op-Amp or Comparator Mode) tRNF Time from reset of discharge latch 1 µs RT Timing Accuracy t Rt (Note 4) -10 +10 % Internal Clock Accuracy t BASE -10 +10 % ELECTRICAL CHARACTERISTICS: CHARGING (4.5V /g163 VDD /g163 16.5V, TA = 0/g176C to +70/g176C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Fast Charge Comparator Threshold VFC Fast charge -127 -121 -115 mV Fast Charge Comparator Hysteresis VHYS-FC Fast charge -31 -28 -25 mV Top-off and Pre-Charge Comparator Threshold VTO Top-off and pre-charge -38 -33 -28 mV Top-off and Pre-Charge Comparator Hysteresis VHYS-TO Top-off and pre-charge -10 -8 -6 mV Discharge Latch Reset Threshold VDCHG-RST -15 -10 -5 mV Discharge Latch Set Threshold VDCHG-SET Reverse current through sense resistor 5 10 15 mV Low Battery Detect Threshold VLB From presence detect into pre-charge 0.95 1.0 1.05 V Cell Detect Threshold V DET 1.50 1.55 1.60 V No Cell Detect Threshold V OPEN 1.60 1.65 1.70 V Presence Detect Threshold Hysteresis VHYS-PD 90 100 110 mV 2.88 2.92 2.96 V Minimum Charge Temp V THM-MIN (Note 5, 6) 0 ºC 1.28 1.32 1.36 V Maximum Charge Temp V THM-MAX (Note 5, 6) 45 ºC 1.12 1.16 1.20 V Over Temp V THM-STOP (Note 5, 6) 50 ºC dT/dt Detect T TERM 0.425 0.5 0.575 ºC/min dT/dt Blanking Time t BLANK 3.85 4.3 4.75 Min Fast Charge Timer Range tFC 0.5 6 Hours Top-Off to Fast Charge Duration Ratio 1:2
DS2715: NiMH Cell Pack Charge Controller 4 of 12 Note 1: Voltages relative to VSS. Note 2: Does not include current through VCH, RT, and DIV pins. Note 3: Below this voltage no I/O pins are active. Note 4: Does not include tolerance of RT resistor. Note 5: VBIAS and resistor tolerances must be added to determine actual threshold. Note 6: Specified temperature thresholds are only valid if recommended thermistor types are used. Note 7: Specification is guaranteed by design. DETAILED PIN DESCRIPTION PIN NAME DESCRIPTION
1 C BIAS Bypass for Internal Voltage Regulator
2 V CH Cell Stack Charge Control Output
3 V SS Ground Reference and Chip Supply Return
4 LED1 Charging Indicator Output
5 LED2 Done Indicator Output
6 V SS Ground Reference and Chip Supply Return
7 CTG Connect to Ground
8 CTG Connect to Ground
9 MODE Mode Select. Connect to VSS for linear mode of operation or CBIAS for comparator mode of operation. 10 DIV Thermistor Divider. Stable output to form a resistor divider for measuring temperature on THM. 11 SNS+ Positive Current Sense. Connect to the pack side of the sense resistor. 12 SNS- Negative Current Sense. Connect to the cell stack side of the sense resistor. 13 V DD Chip Supply Input: +4.0V to +5.5V range. 14 R T Failsafe Timeout. Timeout is selected by an external resistor from R T to VSS. 15 THM Thermistor Input. Connect to a thermistor located in the cell pack and a divider resistor from the Div pin.
16 V BATT
Battery Voltage Sense Input. Connect to a divider from the positive terminal of the cell stack to measure the voltage of a single cell.
Figure 1. BLOCK DIAGRAM
Figure 2. STATE DIAGRAM
4 Sec
DS2715: NiMH Cell Pack Charge Controller 7 of 12 DETAILED DESCRIPTION Charge Cycle Overview The DS2715 regulates the charge of up to 10 NiMH cells in a series configuration. With the mode select pin the DS2715 can be configured to regulate either as an error amplifier in linear mode or as a comparator in switched mode. A charge cycle begins in one of two ways: with the application of power to the DS2715 with cell pack already inserted or with the detection of cell insertion after power-up. 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 each cell reaches 1V. The algorithm proceeds to a fast-charge phase. Fast charging continues as long as the cell pack temperature is less than 50 /g176C based on the THM voltage, the cell voltage as measured by the V BATT pin remains below 1.65V indicating the cell pack is still present. Fast charging terminates by measuring the cell pack’s thermal rate of change dT/dt. When the cell pack’s thermal rate of change exceeds 0.5°C per minute the DS2715 enters top-off. The DS2715 has an internal charge timer as secondary overcharge protection if the charge is not terminated by the dT/dt method. The charge termination timer duration is user selectable from 30 minutes up to 6 hours by an external resistor on the R T pin. The DS2715 remains in top-off for one-half of the period of the fast charge timer duration as selected by the external resistor on R T. After the top-off charge timer expires, the done phase continues indefinitely until the cell pack is removed from the charger or a load is attached. When a load attached to the cell pack, the DS2715 switches to discharge mode. All charge functions are disabled and the regulation FET is driven on to allow the cell pack to discharge. Two LED indicators display the charge status to the user. Undervoltage Lockout (Reset) The UVLO circuit serves as a power-up and brownout detector by monitoring V DD to prevent charging until V DD rises above V UVLO, or when V DD drops below V UVLO - V UVLO-HYS. If UVLO is active, charging is prevented, the state machine is forced to the RESET state, and all charge timers are reset. A 10 /g109s deglitch circuit provides noise immunity. Once VDD reaches an acceptable operating voltage the DS2715 enters the PRESENCE state. Presence The DS2715 enters the PRESENCE state whenever V DD > V UVLO and V BATT > V OPEN indicating that the charge source is present, but no cell is available to charge. The DS2715 will remain in the presence state until a cell is inserted into the circuit causing the voltage on V BATT to fall below 1.55V (V DET) and the cell temperature is inside a valid charging range between 0°C and 45°C (T THM-MIN and T THM-MAX). If both these conditions are met the DS2715 will enter pre-charge. If cells are inserted, but the temperature is outside the valid charging range the DS2715 will remain in the PRESENCE state until the cell temperature falls within the valid charging range. Pre-Charge The DS2715 enters the PRE-CHARGE state when a valid cell voltage is applied to V BATT and the cell temperature as measured by the DS2715 is within the valid charging range. Pre-charge has a 4 second filter to suppress noise on VBATT caused by cell insertion. The DS2715 pre-charges the cell by regulating the voltage drop across the sense resistor to -33mV (VTO) in linear mode or -29mV (V TO - 0.5 x VHYS-TO) in comparator mode. Pre-charge will last until the cell voltage measured by VBATT exceeds 1.0V (VBATT > VLB) at which time the DS2715 will enter FAST CHARGE state. If the cell voltage does not exceed V LB within 30 minutes or if the cell temperature exceeds 50°C at any time during pre-charge, the DS2715 enters the FAULT state. If at any time during pre-charge the voltage on V BATT exceeds 1.65V (V OPEN), the DS2715 determines that the cell pack has been removed and returns to the PRESENCE state. Fast Charge In fast charge mode, the DS2715 regulates the voltage across the sense resistor to -121mV (V FC) in linear mode or -107mV (V FC - 0.5 x V HYS-FC) in comparator mode. LED1 indicates the cell pack is being charged. During fast charge the DS2715 constantly measures the rate of change of the cell temperature (dT/dt). When the cell pack’s dT/dt exceeds 0.5°C per minute (T TERM) the DS2715 enters the TOP-OFF state. The DS2715 ignores changes in the cell temperature caused by charge initiation for the first 4.3 minutes (t BLANK). As secondary overcharge protection, the DS2715 will terminate fast charge and enter top-off based on a time delay set by the external resistor on the R T pin. This resistor value can set the secondary charge termination delay to anywhere from 30 minutes up to 6 hours. If the cell temperature exceeds 50°C at any time during fast charge, the DS2715 enters the
DS2715: NiMH Cell Pack Charge Controller 8 of 12 DONE state. If at any time during fast charge the voltage on V BATT exceeds 1.65V (VOPEN), the DS2715 determines that the cell pack has been removed and returns to the PRESENCE state. Top-Off In top-off mode, the DS2715 regulates the voltage across the sense resistor to -33mV (V TO) in linear mode or - 29mV (VTO - 0.5 x VHYS-TO) in comparator mode. LED1 indicates the cell pack is being charged. The charge timer is reset and restarted with a time-out period of one half the fast-charge duration. When the charge timer expires or if the measured temperature exceeds 50°C, the charger enters the DONE state. DONE/Maintenance The DS2715 enters the DONE state whenever the charge completes normally or if the measured cell temperature exceeds 50°C during the charge. While in the done state V CH is driven to high impedance to prevent further charging of the cell pack and LED is driven on to indicate charge completion. A maintenance charge can be applied to the cells by providing a resistive path from the cell pack to the charge source bypassing the regulator. See the example circuit in Figure 3. The DS2715 remains in DONE until a cell voltage greater than 1.65V (V OPEN) is detected on VBATT indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and waits for the next cell insertion. FAULT The DS2715 enters FAULT if pre-charge is unable to charge the cell above 1.0V (V LB) before the 30 minute pre- charge timeout of if the cell temperature exceeds 50°C during pre-charge. In the fault state V CH is driven to high impedance and LED2 blinks to indicate the fault condition. The DS2715 remains in FAULT until a cell voltage greater than 1.65V (V OPEN) is detected on V BATT indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and waits for the next cell insertion. Discharge Mode When the DS2715 detects a discharge current voltage drop of V DCHG-SET or greater across the sense resistor, charging is terminated and the DS2715 enters the DISCHARGE state. While in this mode, voltage sensing, thermal sensing, and LED outputs are disabled. The V CH pin is driven low to allow the pack to be discharged. Current drain of the DS2715 drops to I DDD. The DS2715 remains in discharge mode until a charge current of at least V DCHG-RST is detected. When this occurs the DS2715 enters the presence detect state to begin a new charge cycle. Application Circuit Figure 3 shows a typical application circuit for charging a 3-cell stack. The mode pin is tied to V SS for linear operation. A 75mΩ sense resistor (R10) sets the charge current at 1.6A. The DS2715 regulates the current through Q1. 68kΩ on R T (R6) sets the fast charge timeout to 102 minutes. R5 and R8 form a 1:3 voltage divider to allow VBATT to measure the voltage of a single cell. The charge source is isolated with diode CR1 to prevent discharge through the source connection. R1 and CR2 form a maintenance charge path to supply the cell pack with ~40mA constant current after the charge completes. Lastly VR1 and R4 create a current leakage path to bias the regulator circuit and prevent an in-rush current spike when the cell stack is connected to the powered circuit.
Figure 3. TYPICAL APPLICATION CIRCUIT FOR A 3-CELL STACK
DS2715: NiMH Cell Pack Charge Controller 10 of 12 CURRENT REGULATION Three basic modes of charging operation are supported by the DS2715: Offline switching through an optocoupler, linear regulation, and DC input switched mode. The DC Switched method requires a cu rrrent-limited power source. Mode of operation is selected through the Mode pin. Connecting the Mode pin to V SS configures the analog block as a transconductance amplifier for linear mode of operation. Connecting the Mode pin to the Cbias pin configures the DS2715 as a comparator for switched mode of operation. Current-Sense Amplifier Mode An error amplifier block provides several options to regulate the charge current. The 20mA open-drain output can drive a PMOS or PNP pass element for linear regulation, or the output can drive an optocoupler for isolated feedback to a primary-side PWM controller. The SNS- pin is a remote-sense return and should be connected to the grounded side of the sense resistor using a separate, insulated conductor. During fast charge, an error signal between the current-sense signal (across the sense resistor) and the internal reference is produced so the voltage across the sense resistor is maintained at V FC in a closed-loop circuit. During top-off the voltage across the sense resistor is maintained at VTO. Current-Sense Comparator Mode The comparator in the DS2715 switches between ON and OFF and is capable of driving a PNP bipolar or a PMOS transistor, enabling the use of a switched-mode power stage. Hysteresis on the comparator input provides noise rejection. In a closed-loop regulation circuit, the comparator regulates voltage across the sense resistor to a DC average of: VRSNS = VFC - 0.5 x VHYS-FC = -0.107V during fast charge VRSNS = VTO - 0.5 x VHYS-TO = -0.029V during top-off Charge Rate Selection The charge rate is determined by an external sense resistor connected between the SNS+ and SNS- pins. The DS2715 will regulate the charge current to maintain a voltage drop of VFC (VFC - 0.5 x VHYS-FC in comparator mode) across the sense resistor during fast charge. The sense resistor can therefore be selected by: Linear Mode: R = V FC / Desired Fast Charge Current Comparator Mode: R = (V FC - 0.5 x VHYS-FC) / Desired Fast Charge Current Charge Time and Top-Off Time Selection Pre-charge has a fixed 30 minute limit generated by an internal oscillator. Charge time and top-off time are controlled by an external resistor from the R T pin to VSS. Resistors can be selected to support fast-charge time-out periods of 0.5 to 6 hours and top-off charge time-out periods of 0.25 to 3 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. If the timer expires in top-off, the DS2715 enters the DONE state. The programmed charge time approximately follows the equation: t = 1.5 x R / 1000 (time in minutes)
thermistors are shown in Table 2. Table 2. THM1, THM2 THRESHOLDS shown in the curve in Figure 4. The left axis is the ratio of the sensed voltage to the divider’s input voltage (VCbias). Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE
DS2715: NiMH Cell Pack Charge Controller 12 of 12 LED1 and LED2 Outputs Open-drain outputs LED1 and LED2 pull low to indicate charge status. When inactive, the outputs are high impedance. LED1 displays the state of charge and LED2 displays the charge results. The LED1 pin drives low in a 1Hz, 50% duty cycle “blink” pattern to indicate cells are charging. LED2 drives low with 100% duty cycle to signal a successful charge completion or blinks at 4Hz, 50% duty cycle to signal a charging fault has occurred. Both LED pins remain in a high-impedance state when no cells are present or the discharge latch is set. LED pins can be tied together if only one LED display is desired. Table 3 summarizes the LED operation for each charge condition. Table 3. LED DISPLAY PATTERNS BASED ON CHARGE STATE
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.