SC1766

BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DESCRIPTION The SC1766 fast charge controller IC is designed for intelligent charging of NiMH or NiCd batteries without overcharging. It detects a voltage drop (-∆V) occurring in the final stage of a fast charging cycle and correspondingly controls the charging current. Fast charge can also be cut off by a peak voltage timer (0∆V). The detection of -∆V is a very reliable method to terminate fast charging for NiMH and NiCd batteries. The SC1766 uses -∆V detection as one of the primary decisions for fast charge cut-off. The -∆V value of the SC1766 is as small as 4mV per cell, particularly suitable for NiMH as well as NiCd batteries. The peak voltage timer is particularly useful when the voltage drop at the end of charge for some batteries, e.g. NiMH cells, is not pronounced enough for reliable detection. An adjustable safety timer (3 settings) is used as a backup termination method. Provisions are made with the SC1766 to prevent fast charge under temperature fault conditions. Two LED outputs are used to indicate the charging status. Another flash LED output can be used alone to indicate charge status. AC mode allows the battery to drive its loads while being charged. Test mode is provided to dramatically reduce production test time. FEATURES • Reliable fast charge control of NiMH/NiCd • batteries Fast charge termination by: 1 Accurate -∆V detection level -0.25% with respect to peak value 2 Peak voltage timer (0∆V) Adjustable fast charge safety timer Protection against temperature fault Protection against short-circuited and open batteries W ide operation voltage range of 9V to 18V, no extra regulator needed Large battery voltage detection range of 0.65V to 3.7V LED drivers to indicate charge status or fault conditions Voltage reference output Quick and easy testing for production Space saving 8-pin and 14-pin SO packages • • • • • • • • • ORDERING INFORMATION DEVICE (1) PACKAGE SO-8 SO-14 SC1766CS08 SC1766CS14 Note: (1) Add suffix ‘TR’ for tape and reel. APPLICATIONS Battery chargers for: • Mobile phones • Notebook and laptop personal computers • Portable power tools and toys • Portable communications equipment • Portable video and stereo equipment ABSOLUTE MAXIMUM RATINGS Parameter Supply Voltage DC Voltage Applied to any Pin Sink Current of VOUT pin, LED pin, and FLASH pin Operating Temperature Range Storage Temperature Range TA TSTG Symbol VCC Maximum 18 18 Units V V 20 mA 0 to 70 -65 to 150 °C °C © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 ELECTRICAL CHARACTERISTICS Unless otherwise specified, TA = 25ºC, VIN = 12.5V Parameter Supply Voltage Supply Current -∆V detection level w.r.t. peak value Voltage protection limits battery low battery high Input impedance of TIMER pin Input impedance of MODE pin Output resistance of LED pin fast charge trickle charge Output resistance of VOUT pin fast charge trickle charge FLASH pin output resistance at fast charge frequency duty cycle Reference voltage source current Temperature fault voltage limits as fraction of VREF under-temperature over-temperature VBT ZTIMER ZMODE RLED 0.50 3.30 100 100 1 25 RVOUT RFLASH 25 1 25 1 50 5.85 1.5 Symbol VDD IDD -0.25 0.65 3.70 0.80 3.90 Min 9 Typ Max 18 1.5 Units V mA % V kΩ kΩ MΩ Ω Ω MΩ Ω Hz % V mA VREF αNTCL 0.60 0.15 0.70 0.20 0.80 0.25 VREF PIN CONFIGURATIONS PIN DESCRIPTIONS VDD Supply voltage input. GND Ground. Input, to sense battery voltage. VBT MODE Input, to set IC operation mode. TIMER Input, for safety timer control. VREF LED VOUT FLASH VNTC Voltage reference output. Output, for LED indicator. Output, for LED indicator. Output, for LED indicator (14-pin only.) Input, for temperature protection (14 pin only). © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 TYPICAL APPLICATIONS Step-Down High-Side Current Sense Battery Charger NOTE: RSENSE = 0.1 ohm, CHARGE CURRENT = 0.5A ±10%, VIN > VBAT +3.5V RSENSE = 0.05 ohm, CHARGE CURRENT = 1.0A ±10%, VIN > VBAT +4.0V RSENSE = 0.033 ohm, CHARGE CURRENT = 1.5A ±10%, VIN > VBAT +4.5V EFFICIENCY > 90%, MEASURED AT CS- NODE Step-Down Rechargeable Battery Charger NOTE: +VIN should be higher than 10V. Z1 is required when +VIN exceeds 18V. Fast charge current is approximately 1A, adjustable through R7. Trickle charge current is adjustable through R12. © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 TYPICAL APPLICATIONS (cont.) Step-Up Rechargeable Battery Charger ** CHARGING CURRENT = 0.8A, AUTO CUT-OFF AT 0.25% - DELTA-V POINT AND FAULT CONDITIONS (RIF SETS THE CHARGING CURRENT). ** VIN MUST BE LOWER THAN VBAT. ** SHORT CIRCUIT CONDITION IS PROTECTED WITH A 2A FUSE. Step-Up/Down Rechargeable Battery Charger ** FAST CHARGE CURRENT =0.8A @VIN < VBAT, = (VIN - VBAT - 0.5)/0.82 @ VIN> VBAT. TRICKLE CHARGE CURRENT = 30mA (RIF SETS FAST CHARGE CURRENT, RIT SETS TRICKLE CHARGE CURRENT). ** TYPICAL EFFICIENCY = 75% ** WITH SHORT CIRCUIT PROTECTION. © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 TYPICAL APPLICATIONS (cont.) Step Down Low-Side Current Sense Battery Charger Discharge Circuit of Rechargeable Battery FINAL VOLTAGE OF BATTERY 6V 5V 4V 3V R26 6.8K 5.1K 3.9K 2.7K Test Circuit NOTE: The final voltage of battery is determined by R26. Discharge current is decided by R5. S1: Push to initiate discharge. Flashing-LED Circuit for Trickle Mode Buzzer Circuit for Trickle Charge Mode NOTE: Frequency (about 1Hz) is determined by R33 and C33. LED will flash when LED pin goes low. NOTE: Frequency (about 1Hz) is determined by R33 and C33. Buzzer will be activated when LED pin goes low. © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 TYPICAL PERFORMANCE CHARACTERISTICS © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 PRINCIPLES OF OPERATION Battery Properties The basic principle of rechargeable battery systems, including NiMH and NiCd cells, is that the processes of charge and discharge are reversible. The charge characteristics of NiMH and NiCd cells look similar in that 1) the cell voltage at the end of charge drops and 2) the cell temperature increases rapidly near the end of charge. The figure below shows the charge voltage and charge temperature characteristics of NiMH and NiCd cells. Notice that the cell voltage decline of NiMH cells at the end of charge is less pronounced than for NiCd cells. Fast battery chargers are available where recharging unit then checks the battery condition to prevent fast charge from taking place under battery fault conditions, i.e. cell voltage fault (VBT< 0.65V or VBT> 3.7V) or cell temperature fault (αNTC > αNTCL or αNTC < αNTCH for the 14-pin version). Temperature fault limits corresponding to αNTCL and αNTCH are determined by an external thermistor divider circuit as included in the typical application circuit. After the battery passes condition fault checks, the VOUT pin goes to low to start fast charge while the initial timer and safety timer of the SC1766 start counting. Both the negative delta voltage detector and the peak voltage timer, however, are disabled until the initial stage of a charge cycle elapses. The SC1766 constantly monitors the voltage at the VBT pin, which rises as battery cells are being fastcharged until the battery full condition is nearly approached. The battery temperature is also constantly sensed to guard against abnormal temperature situations. The VOUT pin will be pulled high by an external pull-up device and the fast charge process will be switched to trickle charge when one of the following situations is encountered: • takes only 1 hour or less with a simple control circuit. One main purpose of the control circuit is to terminate the fast charge process to prevent the temperature and internal pressure of the battery cell from building to a damaging level which degrades or even destroys the battery cell. The SC1766 is a battery fast charge controller IC that utilizes the following methods to terminate the fast charge process for NiMH or NiCd battery cells: 1 Negative delta voltage cut-off (-∆V ), 2 Peak voltage timer cut-off (0∆V ), 3 Maximum temperature cut-off (TCO), 4 Maximum voltage cut-off (VCO), 5 Safety timer cut-off. The principle of operation of the SC1766 is described in the following section. SC1766 Operation When power is first applied to the charge system, consisting of rechargeable battery cells, charge current source, the SC1766 and its associated external circuit, all internal digital circuit blocks of the SC1766 are reset by internal power-on-reset circuitry. The internal control • • • • A negative delta voltage of 0.25% at the VBT pin is detected compared to its peak value (−∆V), The battery voltage stays at its peak value for the duration determined by the peak voltage timer setting (0∆V), The VBT pin voltage exceeds the “high” battery voltage protection limit (VCO), The battery temperature, sensed by the thermistor divider, exceeds the fault temperature range (TCO), The selected safety timer period has finished. TIMER PIN The timer pin can be used as follows to select one of the preset safety timer periods and its corresponding periods of initial timer and peak voltage timer: TIMER pin VDD GND Floating Safety timer 40 min. 80 min. 160 min. Peak V timer 2 min. 4 min. 8 min. Initial timer 1.5 min. 3 min. 3 min. © 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 BATTERY CHARGE CONTROLLER Janaury 30, 1998 SC1766 PRINCIPLES OF OPERATION (cont.) MODE PIN The MODE pin determines the mode in which the IC works: MODE Floating VDD GND Mode NORMAL TEST AC Function normal operation 1/512 safety timer -∆V detector reset timer stops (not reset) OPERATION CHART OF THE SC1766 POWER ON IF 0.65Vα NTCH VOUT goes high for trickle charge. -∆V detector reset. NO Safety timer stops. -∆V detector & peak voltage timer start working after initial period ends. -∆V detector & peak voltage timer working. IF α NTCL >α NTC & α NTC >α NTCH VOUT goes high for trickle charge. -∆V detector reset. NO Safety timer stops. YES IF 0.65