Datasheet

LT3652HV
17
3652hvfa
APPLICATIONS INFORMATION
and 25°C float voltage (V
FLOAT(25°C)
) specified, and using
a convenient value of 2.4k for R
SET
, necessary resistor
values follow the relations:
R
FB1
= –R
SET
• (TC • 4405)
= –2.4k • (–0.0198 • 4405) = 210k
R
FB2
= R
FB1
/ ({[V
FLOAT(25°C)
+ R
FB1
• (0.0674/
R
SET
)] / V
FB
} – 1)
= 210k/({[13.5 + 210k • (0.0674/2.4k)]/3.3} – 1)
= 43k
R
FB3
= 250k - R
FB1
||R
FB2
= 250k – 210k||43k = 215k (see the Battery Float
Voltage Programming section)
While the circuit in Figure 9 creates a linear temperature
characteristic that follows a typical –3.3mV/°C per cell
lead-acid specification, the theoretical float charge voltage
characteristic is slightly nonlinear. This nonlinear charac-
teristic follows the relation V
FLOAT(1-CELL)
= 4 × 10
–5
(T
2
)
– 6 × 10
–3
(T) + 2.375 (with a 2.18V minimum), where
T = temperature in °C. A thermistor-based network can
be used to approximate the nonlinear ideal temperature
characteristic across a reasonable operating range, as
shown in Figure 10.
Status Pins
The LT3652HV reports charger status through two open
collector outputs, the CHRG and FAULT pins. These pins
can accept voltages as high as V
IN
, and can sink up to
10mA when enabled.
The CHRG pin indicates that the charger is delivering
current at greater that a C/10 rate, or 1/10th of the pro-
grammed maximum charge current. The FAULT pin signals
bad battery and NTC faults. These 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
CHARGER STATUS
CHRG FAULT
OFF OFF Not Charging — Standby or Shutdown Mode
OFF ON Bad Battery Fault (Precondition Timeout / EOC
Failure)
ON OFF Normal Charging at C/10 or Greater
ON ON NTC Fault (Pause)
If the battery is removed from an LT3652HV charger that
is configured for C/10 termination, a sawtooth waveform
LT3652HV
196k
198k
6-CELL
LEAD-ACID
BATTERY
22k
B = 3380
3652 F10a
BAT
69k
69k
V
FB
+
TEMPERATURE (°C)
–10
V
FLOAT
(V)
10
5040
60
0 20 30
3652 F10b
12.8
13.0
13.2
13.4
13.6
13.8
14.0
14.6
14.4
14.2
14.8
THEORETICAL V
FLOAT
PROGRAMMED V
BAT(FLOAT)
Figure 10. Thermistor-Based Temperature Compensation Network Programs V
FLOAT
to Closely Match Ideal
Lead-Acid Float Charge Voltage for 6-Cell Charger