SM6780AS Ni-Cd/Ni-MH Battery Charger IC NIPPON PRECISION CIRCUITS INC. OVERVIEW The SM6780AS is a quick charge control IC for Nickel-Cadmium (Ni-Cd) and Nickel Metal Hydride (Ni-MH) rechargeable batteries. It supports quick charge, supplemental and pulse trickle charging modes. The charging mode is selected automatically in response to the battery voltage, temperature and charging time. The quick charge uses either negative delta voltage detection (−∆V), temperature detection (∆T/∆t), or charging time cutoff to control the charging process. In addition, the quick charge mode can be placed on hold, if the battery voltage or battery temperature are abnormal, until normal conditions are restored. The SM6780AS requires few external components to realize a high-stability quick charge battery charger. FEATURES ■ ■ ORDERING INFORMATION VSS INH VDD TEMP PACKAGE DIMENSIONS (Unit: mm) Device Package SM6780AS 8-pin SOP 0.15 + 0.1 − 0.05 0.4 0.2 ■ BATT 4.4 0.2 ■ LEDN 6.2 0.3 ■ ■ CHGN 6780AS ■ TIME 0.695typ 5.2 0.3 0.05 0.05 ■ (Top view) 0.1 ■ Ni-Cd/Ni-MH battery quick charge control −∆V, ∆T/∆t, and maximum charge time cutoffs 3 charge modes (quick charge, supplemental, pulse trickle charge) 3 selectable charge times (80, 120, and 240 minutes) Charge condition LED indicator output (on, pulsed, off) Low power dissipation mode 4.0 to 5.5V operating supply voltage 300sec (typ) −∆V detection invalid time 8mV (typ) −∆V detection accuracy 25mV/min (typ) ∆T/∆t detection accuracy 8-pin SOP package 1.5 ■ ■ PINOUT 1.27 0 to 10 0.10 0.4 0.1 0.12 M NIPPON PRECISION CIRCUITS—1 SM6780AS BLOCK DIAGRAM VDD DC Input VDD TIME CHGN Current Source Reference Regulators Timer Mode Selector OSC CHG Driver BATT VDD Maximum Cell-voltage Check −∆V Function Block Timing Control Logic LEDN Input Select Battery Pack NTC TEMP Temp Check A/D ∆V/∆t Function Block Charge Control Logic LED Driver VDD INH VSS PIN DESCRIPTION Number Name 1 TIME Charge time select 3-level input. HIGH: 240 minutes, MID (VDD /2): 120 minutes, LOW: 80 minutes 2 LEDN Charge indicator LED driver output. Open-drain output. LOW-level output in quick charge mode. 1Hz pulse output when abnormal battery voltage or temperature is detected during quick charge mode. High impedance output in supplemental and trickle charge modes. 3 BATT Battery voltage detector input. Connect a high-impedance resistor voltage divider between the poles of the battery for voltage detection. 4 VSS Ground 5 TEMP Battery temperature thermistor sensor voltage input 6 VDD Supply 7 INH Charge inhibit input. Charging is stopped when HIGH. Charging resumes with the same charge parameters in force prior to the stop when INH goes LOW again. CHGN Charger control output. Open-drain output. Battery charging current flows when CHGN is high impedance. Charge current stops when LOW. High-impedance output in quick charge mode, and pulse output in supplemental and trickle charge modes. 8 Description NIPPON PRECISION CIRCUITS—2 SM6780AS SPECIFICATIONS Absolute Maximum Ratings VSS = 0V Parameter Symbol Condition Rating Unit Supply voltage range V DD −0.3 to 7.0 V Input voltage range V IN −0.3 to 7.0 V Storage temperature range Tstg −55 to 125 °C Operating temperature range Topr 0 to 85 °C Power dissipation PD 150 mW DC Characteristics 1 VDD = 4.0 to 5.5V, VSS = 0V, Ta = 25°C Parameter Symbol Maximum temperature voltage V MXT High-temperature sense voltage Condition Rating Variation Unit V TEMP ≤ V MXT charge cutoff 0.225VDD ±5% V V HTS V HTS ≤ V TEMP ≤ V LTS charge start 0.25VDD ±5% V Low-temperature sense voltage VLTS V TEMP > V LTS charge prohibition 0.4VDD ±5% V Maximum battery voltage V MXV V BATT > V MXV charge cutoff or prohibition 2.0 ±5% V DC Characteristics 2 VDD = 4.0 to 5.5V, VSS = 0V, Ta = 0 to 85°C unless otherwise noted Rating Parameter Symbol Condition Unit min typ max VDD supply voltage VDD 4.0 5.0 5.5 V BATT input voltage VBATT 0 – V DD V TEMP input voltage V TEMP 0.5 – V DD V Disabled when V TEMP < 0.5V INH HIGH-level input voltage V IH1 0.7 – – V INH LOW-level input voltage V IL1 – – 0.1 V TIME HIGH-level input voltage V IH2 V DD − 0.5 – – V TIME MID-level input voltage V IM (VDD /2) − 0.5 – (VDD /2) + 0.5 V TIME LOW-level input voltage V IL2 – – 0.5 V BATT −∆V detection voltage range V DET 1 – 2 V LEDN output pulse frequency fLED – 1 – Hz BATT standby voltage VSTB V DD − 1.5 – V DD − 0.5 V VDD current consumption IDD V DD = 5V, no load – – 0.5 mA VDD standby current ISTB V DD = 5V, V BATT = V DD, no load – – 1 µA LEDN, CHGN sink current IOL VOL = V SS + 0.8V 10 – – mA INH, TIME input leakage current IL V INH = V TIME = V SS to V DD – – ±1 µA −5 – – µA LEDN, CHGN output leakage current IOZ NIPPON PRECISION CIRCUITS—3 SM6780AS FUNCTIONAL DESCRIPTION Charger Operation The SM6780AS battery charger operation starts when the power is applied or when standby mode is released. The charging operation is determined by the BATT and TEMP pin states, and the timer mode selected. Quick charge uses either negative delta voltage detection (−∆V), temperature detection (∆T/∆t), or charging time cutoff to terminate the charging process. The charging mode changes to supplemental charge mode when quick charge mode is completed. After charging starts, the battery voltage and temperature are monitored to check that they are within quick charging rated ranges. If within rated range, quick charge mode is selected. If outside rated range, pulse trickle charge mode is selected. Supplemental mode terminates when the charging time finishes or battery is full, and the charging mode changes to pulse trickle mode. Charging Rate The charging rate is determined by the external charger current source. If the quick charge mode charging rate is considered as unity, then the supplemental charging rate is 1/16, and the pulse trickle charging rate is 1/256. The charging rate for supple- mental and pulse trickle modes are shown in figure 1. The CHGN output is high impedance when the charging current is flowing, and LOW when the current stops. 286µs 286µs Hi-Z Low Quick charge mode 4576µs 73.1ms Supplemental charge mode Pulse trickle mode Start (power ON or battery insertion) Figure 1. CHGN output (external charger control) Charging Status Indicator LED Control (LEDN) The SM6780AS LEDN output can be used to drive a charging status indicator LED. The LED timing when power is applied or standby mode is released is shown in figure 2. In quick charge mode, the LEDN output is LOW and the LED turns ON. If the battery temperature or battery voltage exceeds the charging rated ranges, the LEDN output pulses at a frequency of 1Hz to indicate battery out-of-range condition. In supplemental and pulse trickle modes, the LEDN output is high impedance and the LED turns OFF. Hi-Z LED OFF LED ON Depends on charge mode Low Approximately Approximately 3.5 s 1.5 s Power ON or Standby mode cancel Figure 2. LEDN output timing NIPPON PRECISION CIRCUITS—4 SM6780AS Battery Voltage and Temperature Detection The battery voltage detector input is BATT. The charger treats the input voltage as the equivalent voltage of a single cell. For multiple cells (connected in series), a high-resistance (> 100kΩ) battery divider can be used to input the voltage equivalent of a single cell, as shown in figure 3. Ra BATT pin Battery Rb Ra =N−1 Rb N:Number of cells Figure 3. BATT connection example The battery temperature detector input is TEMP. The input voltage is provided by a negative temperature coefficient thermistor (NTC thermistor) located in close proximity to the battery, as shown in figure 4. The input voltage range is 0.5V to VDD. Rc TEMP pin Battery Rd NTC Figure 4. TEMP connection example Note that the thermistor temperature characteristics are non-linear, so a correction resistance Rc should be used for linearity correction. The temperature rating of resistances Rc and Rd should be chosen to match the battery temperature range rating. If the temperature detection function is not used, the TEMP input should be fixed at a potential in the range 0.25VDD to 0.4VDD. NIPPON PRECISION CIRCUITS—5 SM6780AS Charging Modes The SM6780AS has 3 modes of operation: quick charge, supplemental charge, and pulse trickle mode. CHGN output Cell voltage The SM6780AS uses the various detection functions to monitor the state of the battery and select the charging mode automatically. In quick charge mode, charging occurs at a rate set by the external current source. In supplemental charge mode, the battery is charged by current pulses to the full stable capacity of the chemical substances within the battery. Pulse trickle mode maintains the level within the battery, compensating for internal losses. Hi-Z Low Supplemental charge mode Quick charge mode Quick charge mode end Start Pulse trickle mode Charge complete Figure 5. Charging mode, battery voltage and charging current Quick (Supplemental) Charge Conditions — Battery Check The SM6780AS monitors the battery voltage and battery temperature to confirm the values are within the rated range of the battery during quick charge and supplemental charging modes to realize a highstability battery charger. If the battery voltage or battery temperature charging rating is exceeded before quick charging mode terminates, the charging mode is placed on hold. The VBATT internal timer continues to operate, and pulse trickle charging occurs. The LEDN output pulses at a rate of approximately 1Hz. If the charging rating is exceeded during supplemental charging mode, the mode terminates and charging switches to pulse trickle mode. VTEMP Low temperature sense Voltage (0.4 × VDD) Maximum cell Voltage 2.0V Charge valid range Charge valid range High temperature sense Voltage (0.25 × VDD) Maximum temperature Voltage (0.225 × VDD) 0V Pulse trickle mode Power ON Quick charge mode Quick charge start Pulse trickle mode Quick charge is suspended Quick charge mode Quick charge restart High-temperature quick charge hold state: V TEMP < V MXT (0.225 × V DD ) High-temperature quick charge hold release state: VTEMP > V HTS (0.25 × V DD ) Figure 6. Quick (supplemental) charge ranges NIPPON PRECISION CIRCUITS—6 SM6780AS −∆V Invalid Time Generally, the battery voltage becomes unstable just after quick charging starts, so the −∆V battery voltage detection is disabled for 5 minutes to avoid error in battery voltage detection. However, the ∆T/∆t temperature detection function continues to operate. After the −∆V detection is enabled, both detection functions operate. −∆V Detection (BATT) Note that −∆V detection is disabled for 5 minutes when quick charge mode is first started to avoid error in battery voltage detection, as described in the previous section. 8mV Vpeak Cell voltage After Ni-Cd and Ni-MH batteries are fully charged in quick charge mode, the battery voltage begins to drop after reaching a peak value. The SM6780AS monitors the delta voltage (−∆V) to help determine when the battery is fully charged. When the voltage has fallen a minimum of 8mV (typ), the battery is fully charged and quick charge mode terminates. − ∆V detect Quick charge time Figure 7. Battery voltage change ∆T/∆t Detection (TEMP) When Ni-Cd and Ni-MH batteries are close to full charge in quick charge mode, the temperature of the battery begins to greatly increase. The SM6780AS monitors the temperature change rate (∆V/∆t) to help determine when the battery is fully charged. When the temperature voltage on TEMP decreases by a minimum of 25mV (typ) within a 60-second interval, the battery is considered to be fully charged and quick charge mode terminates. Note that the TEMP voltage decreases with increasing temperature due to the negative temperature coefficient of the thermistor. Cell voltage Cell voltage ∆t ∆T Cell temperature Quick charge time Figure 8. Battery temperature change Voltage Voltage 25mV 60s VTEMP Quick charge time ∆T/∆t detect Figure 9. VTEMP change NIPPON PRECISION CIRCUITS—7 SM6780AS Maximum Charging Time (TIME) The SM6780AS supports 3 different maximum charging time settings, in quick charge and supplemental charge modes, which can be selected on the 3-level input TIME (HIGH, MID, LOW). HIGH level is achieved by pull-up, LOW level by pull- down, and MID level by a high-resistance voltage divider arrangement to set the voltage at VDD/2. The voltage level on TIME should only be switched in standby mode. VDD = 5V, Ta = 25°C Quick charge/supplemental charge time (minutes) TIME voltage level min typ max HIGH 192 240 288 MID 96 120 144 LOW 64 80 96 Quick (Supplemental) Charge Inhibit (INH) When INH goes HIGH, quick charge mode or supplemental charge mode operation stops. While INH is HIGH, the internal timer stops and pulse trickle charging occurs. When INH goes LOW, the charging mode is restored to the previously active mode and the internal timer restarts. Standby Mode When the BATT input voltage is ≥ VSTB, the SM6780AS is in standby mode. In this mode, the internal timer is reset, and the LEDN and CHGN outputs become high impedance. Standby mode is released when the voltage applied to BATT falls below VSTB. NIPPON PRECISION CIRCUITS—8 SM6780AS Charging Flow Diagram Supply applied Standby mode released LED ON Battery check (maximum battery voltage: VBATT ≥ 2V) and (battery temperature: 0.225VDD ≤ VTEMP ≤ 0.4VDD) continuously battery check operation Not OK OK Maximum quick charge time count start Initial timer (5 minutes) count start − ∆V detection disabled ∆T/∆t detection enabled Battery check OK Maximum battery voltage: VBATT ≥ 2V and battery temperature: 0.25VDD ≤ VTEMP ≤ 0.4VDD Battery out-of-range Pulse trickle mode charging LEDN = pulse (flashing) CHGN = pulse Quick charge mode LEDN = LOW (ON) CHGN = High impedance Battery check not OK − ∆V detection or ∆T/∆t detection or maximum charge time passed Maximum charging time passed Maximum supplemental charge time count start Supplemental mode LEDN = High impedance (OFF) CHGN = pulse Battery check not OK or maximum charging time passed Charging terminates Pulse trickle mode charging LEDN = High impedance (OFF) CHGN = pulse NIPPON PRECISION CIRCUITS—9 SM6780AS Charging Operating Status Conditions Battery check OK Charging mode CHGN output1 LEDN output Internal timer INH Quick charge LOW Yes Quick charge High impedance LOW (ON) Count Quick charge hold LOW No Pulse trickle 13.68Hz, 3.91% duty 1Hz (pulsing) Count Quick charge inhibit HIGH – Pulse trickle 13.68Hz, 3.91% duty Same condition as when INH went HIGH Hold Supplemental charge LOW OK Supplemental 218Hz, 6.25% duty High impedance (OFF) Count Supplemental charge inhibit HIGH OK Pulse trickle 13.68Hz, 3.91% duty High impedance (OFF) Hold Pulse trickle – – Pulse trickle 13.68Hz, 3.91% duty High impedance (OFF) – Standby – – – High impedance High impedance (OFF) Reset Charging status 1. Frequency and duty are typical values. TYPICAL APPLICATION CIRCUIT External current source VBB 12V R1 5.1kΩ 78L05 Q1 2SC945 IN Q2 2SD525 OUT VSS 5V VBEQ2 ICHG = R2 4/5W = 5 − VBEQ2 R2 5 − 0.65 4 ICHG VDD 5V R6 33kΩ R5 1.8kΩ Q3 2SC945 R7 100kΩ SW2 SM6780AS 6 R3 100kΩ SW1 R4 100kΩ 2 1 4 VDD CHGN LEDN INH TIME TEMP VSS BATT 8 R12 12kΩ R8 100kΩ 7 5 3 R9 200kΩ R10 200kΩ R9 =N−1 R10 N= Number of cells NTC R:10kΩ (at 25 C) B:3435K R13 14kΩ R11 640Ω Note that the above circuit is an example circuit to demonstrate the connections for device functions. Battery charger operation is not guaranteed. NIPPON PRECISION CIRCUITS—10 SM6780AS NIPPON PRECISION CIRCUITS INC. reserves the right to make changes to the products described in this data sheet in order to improve the design or performance and to supply the best possible products. Nippon Precision Circuits Inc. assumes no responsibility for the use of any circuits shown in this data sheet, conveys no license under any patent or other rights, and makes no claim that the circuits are free from patent infringement. Applications for any devices shown in this data sheet are for illustration only and Nippon Precision Circuits Inc. makes no claim or warranty that such applications will be suitable for the use specified without further testing or modification. The products described in this data sheet are not intended to use for the apparatus which influence human lives due to the failure or malfunction of the products. Customers are requested to comply with applicable laws and regulations in effect now and hereinafter, including compliance with export controls on the distribution or dissemination of the products. Customers shall not export, directly or indirectly, any products without first obtaining required licenses and approvals from appropriate government agencies. NIPPON PRECISION CIRCUITS INC. NIPPON PRECISION CIRCUITS INC. 4-3, Fukuzumi 2-chome Koto-ku, Tokyo 135-8430, Japan Telephone: 03-3642-6661 Facsimile: 03-3642-6698 NC9918AE 2000.05 NIPPON PRECISION CIRCUITS—11