LTC4020_15 Datasheet, PDF (29/42 Pages) Linear Technology – 55V Buck-Boost Multi-Chemistry Battery Charger

LTC4020
APPLICATIONS INFORMATION
LTC4020
RNG/SS
SERVO
REFERENCE
4020 F16
Figure 16. Driving the RNG/SS Pin with a Current Sink Active
Servo Amplifier
RNG/SS: Soft-Start
Soft-start functionality is also supported by the RNG/SS
pin. 50µA is sourced from the RNG/SS pin, so connect-
ing a capacitor from the RNG/SS pin to ground (C_RNG/SS)
creates a linear voltage ramp. The maximum charge current
follows this voltage, thus increasing the charge current
capability from zero to the full programmed value as the
capacitor gets charged from 0 to 1V. The value of C_RNG/SS
is calculated based on the desired time to full current (T_SS)
following the relation:
C_RNG/SS = 50µA • T_SS
The RNG/SS pin is pulled to ground internally when charg-
ing is terminated so each new charging cycle begins with
a soft-start cycle. RNG/SS is also pulled to ground during
bad battery and NTC fault conditions.
LTC4020
RNG/SS
C_RNG/SS
4020 F17
Figure 17. Using the RNG/SS Pin for Soft-Start
Status Pins
The LTC4020 reports charger status through two open
collector outputs, the STAT1 and STAT2 pins. These pins
can accept voltages as high as 55V when disabled, and
can sink up to 5mA when enabled.
If the LTC4020 is configured for a CC/CV charging algo-
rithm, the STAT1 pin is pulled low while battery charge
currents exceed 10% of the programmed maximum (C/10).
The STAT1 pin is also pulled low during NTC faults. The
STAT2 pin is pulled low during NTC faults or after a bad
battery fault occurs. The STAT1 pin becomes high imped-
ance when a charge cycle is terminated or when charge
current is below the C/10 threshold, and the STAT2 pin
remains high impedance if no fault conditions are present.
If the LTC4020 is configured for a CC charging algorithm,
the STAT1 pin is pulled low during the entire charging
cycle, and the STAT2 pin is pulled low during NTC faults.
The STAT1 pin becomes high impedance when the charge
cycle is terminated.
If the LTC4020 is configured for a lead-acid charging
algorithm, the STAT1 and STAT2 pins are used as charge
cycle stage indicator pins. The STAT1 pin is pulled low
during the bulk and absorption charging stages and is high
impedance during the float charging period and during NTC
or bad battery faults. The STAT2 pin is pulled low during
bulk and float charging stages, and is high impedance
during the absorption charging stage and during NTC or
bad battery faults.
The STAT1 and STAT2 status pins are binary coded, and
signal following the table below, where ON indicates pin
pulled low, and OFF indicates pin high impedance:
STATUS PINS STATE
STAT1
STAT2
OFF
OFF
OFF
ON
ON
OFF
ON
ON
CC/CV
(MODE = 0V)
Not Charging — Standby or
Shutdown Mode, I_CS < C/10
Bad Battery Fault
Charging Cycle OK: Trickle Charge or
I_CS > C/10
NTC Fault
LEAD-ACID
(MODE = INTV_CC)
Not Charging — NTC/Bad Battery Fault
or Shutdown
Float Charge
Absorption Charge
Bulk Charge
CC
(MODE = -NC-)
Not Charging — Standby or
Shutdown Mode, I_CS < C/10
Not Used
Charge Cycle OK
NTC Fault
For more information www.linear.com/LTC4020
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