LTC4110EUHF LINER [Linear Technology], LTC4110EUHF Datasheet - Page 44

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

LTC4110
APPLICATIONS INFORMATION
that the power dissipated is never allowed to rise above
the manufacturer’s recommended maximum level.
Switching transition time is another consideration. When
the LTC4110 senses a need to switch any PowerPath
MOSFETs on or off time delays are encountered. MOSFETs
with higher Q
DCOUT to hold up all the system’s power supply function
during the transition. The transition time of a MOSFET to
an on or off state is directly proportional to the MOSFET
gate charge. Switching times are given in the Electrical
Characteristics Table (see t
TRANSFORMER
There are two ways to design a transformer.
1. Design it yourself.
2. Work with a transformer vendor to identify an off-
Even if you choose to design it yourself, you still have to
fi nd a transformer manufacturer to make it for you.
We recommend contacting a transformer manufacturer
directly since they often have online tools that can help
you quickly fi nd and select the right transformer. There are
many off the shelf transformers that can be successfully be
used with the LTC4110. Table 10 shows some suggested
off the shelf transformers.
If you want to design a custom transformer optimized
for your design, Application Note 19 has an example of
how to design a Flyback transformer in the “Transformer”
section.
Table 10. Recommended Components Values for 12V Input Supply Li-Ion Battery Backup System Manager
Cell
3
3
3
4
4
4
Note: 1:1 turns ratio for all the transformers listed in the table..
44
the-shelf transformer.
MAX (I
CHG
1
2
3
1
2
3
GATE
, I
CAL
) (A) R
will require more bulk capacitance on
SNS(BAT)
dDON
100
100
50
33
50
33
(mΩ) R
, t
dDOFF
SNS(FET)
).
50
25
15
50
25
15
(mΩ)
TRANSFORMER INDUCTANCE (μH)
Regardless of which way you go, we offer the following
thoughts.
Turns ratio affects the duty factor of the power converter
which impacts current and voltage stress on the power
MOSFETs, input and output capacitor RMS currents and
transformer utilization (size vs power). Using a 50%
duty factor under nominal operating conditions usually
gives reasonable results. For a 50% duty factor, the turns
ratio is:
V
for the design operating in charging mode and in calibration
mode. The fi nal turns ratio should be chosen so that it is
approximately equal to the average of the two calculated
values for N. In addition, choose a turns ratio which can
be made from the ratio of small integers. This allows
bifi lar windings to be used in the transformer, which can
reduce the leakage inductance and the need for aggressive
snubber design, thus improving effi ciency.
Avoid transformer saturation under all operating conditions
and combinations (usually the biggest problems occur at
high output currents and extreme duty cycles). Choose
the magnetizing inductance so that the current ripple is
about 20% of DC current.
Finally, in low voltage applications, select a transformer
with low winding resistance. This will improve effi ciency
at heavier loads.
BAT
24
12
24
12
9
9
N
is the nominal battery voltage. N should be calculated
=
V
V
DCIN
BAT
TRANSFORMER VENDOR AND PART NUMBER
BH 510-1019 TDK PCA14.5/6ER-U03S002
COILTRONICS VPH4-0140-R
COILTRONICS VPH4-0075-R
COILTRONICS VP4-0140-R
COILTRONICS VP5-0155-R
TDK PCA20EFD-U04S002
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