LTC4110EUHF LINER [Linear Technology], LTC4110EUHF Datasheet - Page 35

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

APPLICATIONS INFORMATION
the highest current fl ow between charge and calibration
modes, whichever is greater.
See Table 10 for example values.
R
development of an accurate host software based capacity
measurements of standard batteries. Use resistors with
1% accuracy or better or use a 4-terminal Kelvin sensing
resistor. See the PCB Layout section for a reasonable no
cost Kelvin sensing layout that permits the use of less
expensive standard two terminal sense resistors. For more
electrical information relating to R
Component Selection section.
As designed, any signifi cant AC ripple voltage seen by
CSP and CSN pins can lead to current sensing errors for
both current programming and capacity measurements.
To prevent the Flyback’s AC ripple voltage from interfering
with DC accuracy, R
installed between the R
The CSP and CSN pins have an input bias current of ±10nA
typically. A very large R
large current mismatch error. The current fl owing into
the CSP and CSN pins equals V
100mV/(R
will result in a large current. Typically a value between 3k
and 30k gives the best performance.
SNS(BAT)
R
SNS BAT
(
accuracy is intentionally made very high to permit
CSP1
)
=
+ R
LTC4110
100
I
CSP2
MAX
SNS(BAT)
mV
), a very small R
SNS(BAT)
CSP1
CA
must have a RC fi lter network
+ R
+
–
and CSP and CSN pins.
CSP2
SNS
SNS(BAT)
/(R
value will cause a
CSP1
CSP1
itself, see the
+ R
+ R
Figure 12. CSP , CSN RC Filter
CSP2
R
R
CSN2
CSP2
2k
2k
CSP2
value
) =
C
330n
C
330n
CSN
CSP
Recommended starting values for the fi lter is:
R
R
C
Figure 12 shows typical values for C
R
The LTC4110’s Flyback converter operates in current mode
with R
rent in both Charge and Calibration modes. The LTC4110’s
I
primary current as required by the feedback loop. Second
is to monitor the secondary current and check for short
circuits. The traditional Flyback primary and secondary
currents look like the following:
The waveforms in Figure 13 each assume a view of posi-
tive current fl ow into the load. The value N represents the
ratio of the secondary to the primary with the primary
set to a value of 1. Unlike a traditional Flyback topology,
the LTC4110 Flyback is bi-directional, so the meaning of
“primary” is a function of the operating mode. In order
SENSE
CSP
CSP1
CSP1
SNS(FET)
RCSN1
R
CSP1
1k
1k
= C
SNS(FET)
Figure 13. Flyback Primary and Secondary Current
+ R
= R
pin serves two functions. First is to regulate the
CSN
0
0
CSP2
CSN1
= about 3 • C
monitoring cycle-by-cycle transformer cur-
R
100mV
= R
between 1K and 2K
ΔI
SNS(BAT)
CSN1
I
PRI
+ R
ITH
CSN2
.
I
PRI
N
= about 3K
PRIMARY CURRENT
SECONDARY CURRENT
ITH
4110 F12
LTC4110
= 0.1μF
4110 F13
35
4110fa