LTC4110
38
4110fb
R
SNS(BAT)
= resistor between fl yback transformer and
battery
R
CSP
= R
CSP1
+ R
CSP2
R
CSN
= R
CSN1
+ R
CSN2
R
ICHG
= resistor connected between I
CHG
pin and GND
R
IPCC
= resistor connected between I
PCC
pin and GND
R
ICAL
= resistor connected between I
CAL
pin and GND.
If any programming resistor value on any of the three
pins exceeds 100k, see Flyback Compensation section
for more information.
Pins can be tied together to save components if any of
the currents have the same value. If two pins share a
common programming resistor greater than 100k, only
one compensation circuit is required.
If the TYPE pin is set for SLA/LEAD ACID, then the I
PCC
pin is not used. You can leave the I
PCC
pin open.
PROGRAMMING BACKUP MODE ENTRY THRESHOLD
AND CALIBRATION MODE BACK-DRIVE VOLTAGE
DETECTION THRESHOLD
A resistor divider connected to supply input sets both the
backup mode entry threshold and the calibration mode
back-drive voltage detection threshold.
V
BACKUP
=
R2
R1
+
1
• V
BGR
V
BACKDRIVE
=
V
OVP
V
BGR
• V
BACKUP
R2
R1
=
V
BACKUP
V
BGR
1
where:
V
BACKUP
= supply voltage when backup starts, it should
not be programmed to less than 4.5V
V
BACKDRIVE
= supply voltage when calibration is terminated,
it should not be programmed to more than 20V
V
OVP
= DCDIV pin back-drive detect threshold in calibration
mode, typically 1.5V (see V
OVP
)
fl oat voltage = 2.5V at 25°C with a temperature coeffi cient of
–2mV/°C, then R1 = 7256, k1 = 0.580, TCk1 = –10.3m/°C,
Δ
V
FLOAT
= 2.5 – 2.35 = 0.15V, k2 = 0.162, k3 = 0.634.
PROGRAMMING CURRENT
Charge/calibration currents are programmed using the
following equations:
I
V
R
R
R
I
V
R
CHG
BGR
SNS BAT
CSP
ICHG
PCC
BGR
SNS B
=
=
(
)
(
•
A
AT
CSP
IPCC
CAL
BGR
SNS BAT
CSN
ICAL
R
R
I
V
R
R
R
)
(
)
•
•
=
where:
I
CHG
= bulk charge current
I
PCC
= preconditioning charge current
I
CAL
= calibration current
V
BGR
= 1.220V
APPLICATIONS INFORMATION
Figure 16. Lead Acid Temperature Compensation
4110 F16
R
NTC
10k
–
+
–
+
(1 – k3) • R
VREF
k3 • R
VREF
R2
R2 + R3
R1
R2
R3
R0
R0 + R1
k2 =
k1 =
V
REF
V
CHG
THB
THA
