Datasheet LTC4020 (Analog Devices) - 8

LTC4020
pin FuncTions TG1 (Pin 1):
VIN side (step-down) primary switch FET value can range from 50kΩ (500khz) to 500kΩ (50khz). gate driver output. RRT = 100kΩ yields 250kHz operating frequency. See
BST1 (Pin 2):
Boosted supply rail for V Applications Information. IN side (step-down) switch FETs. Connect 1µF capacitor from this pin to SW1.
SHDN (Pin 9):
Precision Threshold Shutdown Pin. En- Connect 1A Schottky diode cathode to this pin, anode to able threshold is 1.225V (rising), with 100mV of input INTVCC pin. hysteresis. When in shutdown, all charging functions are
SENSGND (Pin 4):
Kelvin connection for PGND used for disabled and input supply current is reduced to 27.5µA. SENSBOT current sense reference. Typical SHDN pin input bias current is 10nA.
SENSBOT (Pin 5):
Ground Referred Current Sense Amplifier
VIN_REG (Pin 10):
Input Voltage Regulation Reference. Input. Inductor current is monitored via a PGND referenced Battery charge current is reduced when the voltage on current sense resistor (R this pin falls below 2.5V. Connecting a resistor divider SENSEB), typically in series with the source of the V from VIN to this pin enables programming of minimum IN side synchronous switch FET. Kelvin connect this pin to the associated sense resistor. Inductor operational VIN voltage for the battery charging function. current is limited to a maximum average value (I This is used to program the peak power voltage for a LMAX), and corresponds to 50mV across this sense resistor during solar panel, or to help maintain a minimum voltage on normal operation. a poorly regulated input supply. This pin should not be used to program minimum operational VIN voltage with RSENSEB = 0.05/ILMAX low impedance supplies. Should the input supply begin to Set R collapse, the LTC4020 reduces the DC/DC converter input SENSEB = RSENSEA, as described in SENSTOP pin description. A filter capacitor (C power such that programmed minimum V SENSB) is typically con- IN operational nected from SENSBOT to SENSGND for noise reduction. voltage is maintained. If the voltage regulation feature is not used, connect the VIN_REG pin to VIN or INTVCC. Typical CSENSB ~ 1nS/RSENSEB VIN_REG pin input bias current is 10nA. See Applications See Applications Information section. Information.
SENSTOP (Pin 6):
V
MODE (Pin 11):
Charger Mode Control Pin. Short this pin IN Referred Current Sense Amplifier Input. Inductor current is monitored via a V to ground to enable a constant-current/constant-voltage IN referenced current sense resistor (R (CC/CV) charging algorithm. Connect this pin to pin INTV SENSEA), typically in series with CC the drain of the V to enable a 4-step, 3-stage lead-acid charging algorithm. IN side primary switch FET. Kelvin con- nect this pin to the associated sense resistor. Inductor Float this pin to force a constant-current (CC) charging current is limited to a maximum average value (I function. See Applications Information section. LMAX), and corresponds to 50mV across this sense resistor dur-
STAT1 (Pin 12):
Open-collector status output, typically ing normal operation. pulled up through a resistor to a supply voltage. This status R pin can be pulled up to voltages as high as 55V when the SENSEA = 0.05/ILMAX pin is disabled, and can sink currents up to 1mA when logic Set RSENSEA = RSENSEB, as described in SENSBOT pin low (<0.4V). Pull down currents as high as 5mA (absolute description. maximum) are supported for higher current applications,
SENSVIN (Pin 7):
Kelvin connection for input supply (V such as lighting LEDs. IN) used for SENSTOP current sense reference. Input power If the LTC4020 is configured for a CC/CV charging algo- supply pin for most internal low current functions. Typical rithm, the STAT1 pin is pulled low while battery charge pin bias current is 0.25mA. currents exceed 10% of the programmed maximum (C/10).
RT (Pin 8):
System Oscillator Frequency Control Pin. The STAT1 pin is also pulled low during NTC faults. The Connect resistor (R STAT1 pin becomes high impedance when a charge cycle RT) from this pin to ground. Resistor 4020fd 8 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