Datasheet LTC4020 (Analog Devices) - 10

LTC4020
pin FuncTions
The RNG/SS pin is pulled low during periods when charg- Trickle Charge Voltage (VTRK) = 1.75V ing is disabled, including NTC faults, bad battery faults, Auto-Restart Voltage (V and normal charge cycle termination. This allows for a RESTART) = 2.4375 graceful start after faults and when initiating new charge During lead-acid charging, the battery voltage references cycles, should soft-start functionality be implemented. are: Both a soft-start capacitor and a programming resistor Absorption Voltage (VABSOR) = 2.5V can be implemented in parallel. Float Charge Voltage (VFLT) = 2.3125V RNG/SS voltage can also be manipulated using an active Trickle Charge Voltage (V device, such as employing a pull-down transistor to dis- TRK) = 1.75V able charge current or to dynamically servo maximum Bulk Recharge Voltage (VBULK) = 2.1875V charging current. Because this pin is internally pulled to With RFB1 connected from BAT to VFB and RFB2 connected ground during fault conditions, active devices with low- from VFB to FBG, the ratio of (RFB1/RFB2) for the desired impedance pull up capability cannot be used. programmed battery float voltage (CC/CV charging) or See Applications Information section. absorption voltage (lead-acid charging) follows the relation:
NTC (Pin 16):
Battery Temperature Monitor Pin. Connect RFB1/RFB2 = (VFLOAT/ABSORB)/2.5 – 1 (V) a 10kΩ, β = 3380 NTC thermistor from this pin to ground.
FBG (Pin 18):
Voltage Feedback Divider Return. This pin The NTC pin is the input to the negative temperature coef- contains a low impedance path to signal ground, used ficient temperature monitoring circuit. This pin sources as the ground reference for voltage monitoring feedback 50µA, and monitors the voltage created across the 10kΩ resistor dividers. When VIN is not present or the LTC4020 thermistor. When the voltage on this pin is above 1.35V is in shutdown, this pin becomes high impedance, elimi- (0°C) or below 0.3V (40°C), charging is disabled and an nating current drain from the battery associated with the NTC fault is signaled at the STAT1 and STAT2 status pins. feedback resistor dividers. If the internal timer is being used, the timer is paused,
VFBMIN (Pin 19):
Minimum voltage feedback pin for instant- suspending the charging cycle until the NTC fault condi- on operation. Minimum DC/DC converter output voltage tion is relieved. There is approximately 5°C of temperature (VOUTMIN) is programmed using this pin for instant-on hysteresis associated with each of the temperature thresh- functionality. VOUTMIN is programmed through a feedback olds. The NTC function remains enabled while thermistor resistor divider placed from the CSP pin to FBG. resistance to ground is less than 250kΩ. If this function is not desired, leave the NTC pin unconnected or connect If the battery voltage is below the voltage level programmed a 10k resistor from the NTC pin to ground. The NTC pin using this pin, the LTC4020 controls the external Pow- contains an internal clamp that prevents excursions above erPath FET as a linear pass element, allowing the DC/DC 2V, so the pin must not be pulled high with a low imped- converter output to achieve the minimum programmed ance source. A low impedance element can be used to voltage. Maximum battery charge current is reduced as pull the pin to ground. the voltage across the PowerPath FET increases to control power dissipation.
VFB (Pin 17):
Battery Voltage Feedback Pin. Battery volt- ages are programmed through a feedback resistor divider The internal VFBMIN voltage reference is 2.125V. With a placed from the BAT pin to FBG. resistor (RMIN1) connected from CSP to VFBMIN, and a resistor (RMIN2) connected from VFBMIN to FBG, the ratio During CC/CV charging, the battery voltage references are: of these resistors for the desired minimum converter Float Voltage (V output voltage follows the relation: FLOAT) = 2.5V RMIN1/RMIN2 = (VOUT(MIN)/2.125) – 1 4020fd 10 For more information www.linear.com/LTC4020 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Electrical Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts