LTC4110EUHF LINER [Linear Technology], LTC4110EUHF Datasheet - Page 37

• Manufacturer Part Number: LTC4110EUHF
• Description: Battery Backup System Manager
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
PROGRAMMING CHARGE VOLTAGE
Depending on the battery chemistry chosen by the TYPE
pin, a charge termination voltage or a fl oat voltage will be
required. The difference between the two is time. A fl oat
voltage is applied to a battery forever. The V
to set any of these voltages and the equations remain the
same. For this document, we will use the term fl oat voltage
generically. If nickel chemistry is chosen, the V
disabled placing the charger in constant current mode. If
you are using a smart battery, wake-up charge is subject
to the V
Connecting the V
cell fl oat voltage (4.2V for Li-ion, 2.35V for SLA). If a dif-
ferent fl oat voltage is needed, tie the V
between 0.25 V
on the V
voltage of the same voltage as V
(±0.5%) tolerance than V
where
ΔV
V
V
The resistor divider connected to V
(see the Programming Charge Time with TIMER and V
Pins section for more details).
THERMISTOR FOR LEAD ACID BATTERIES
When the TYPE pin is programmed for Lead Acid, THA
pin will be force to V
NTC resistance. The value of R1 is given by:
where:
R0 = thermistor resistance (Ω) at T0
T0 = thermistor reference temperature (°K)
CHG
BGR
R1= R0 •
FLOAT
V
= V
= 1.220V
FLOAT
CHG
REF
= Adjusted Float Voltage – Default Float Voltage
CHG
pin. Unlike V
pin setting when active.
= 2 •
β − 2 • T0
β + 2 • T0
Pin Voltage,
BGR
CHG
and 0.75 V
V
V
CHG
BGR
BGR
pin to GND will set the default per
REF
, THB will be used to sense the
REF
, V
1 • 0.6
.
BGR
BGR
REF
using a resistor divider
is an internal reference
but with a much tighter
REF
CHG
pin will affect timer
pin to a voltage
CHG
pin is used
CHG
pin is
REF
β = exponential temperature coeffi cient of resistance
The LTC4110 is designed to work best with a 5% 10k NTC
thermistor with a β near 3750, such as the Siemens/EPCOS
B57620C103J062. In this case, R1 = 7256Ω.
LEAD ACID BATTERY TEMPERATURE COMPENSATION
To program the temperature compensation for SLA charg-
ing, an external circuit is needed as shown in Figure 16.
The values are given by:
where:
TCV
(Range: –2mV/°C – –6mV/°C)
ΔV
2.35V (Range: –0.15V – 0.15V)
For example, if a 10k NTC with β = 3750 is used, desired
R1= R0 •
k1=
k2 =
k3 =
FLOAT
TCk1= –
R
FLOAT
R1
NTC
R0 + R1
1.2 • TCk1
0.5 + ΔV
TCV
= fl oat voltage at 25°C – default fl oat voltage
R0
= temperature coeffi cient of the fl oat voltage
THA
THB
(R1+ R0)
FLOAT
β − 2 • T0
β + 2 • T0
REF LO_REF
Figure 15. Lead Acid Thermistor
+
β • R1• R0
FLOAT
HI_REF
V
BGR
1− k2
2
• T0
/ 1.2 − k1• k2
+
–
+
–
2
TH_HI
TH_LO
LTC4110
LOGIC
RES_OR
RES_HOT
37
4110 F15
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