LTC3300-2_15 Datasheet, PDF (29/42 Pages) Linear Technology – Addressable High Efficiency Bidirectional Multicell Battery Balancer

LTC3300-2
APPLICATIONS INFORMATION
Good design practice recommends increasing this voltage
rating by at least 20% to account for higher voltages present
due to leakage inductance ringing. See Table 7 for a list of
FETs that are recommended for use with the LTC3300-2.
Table 7
PART NUMBER
SiR882DP
SiS892DN
IPD70N10S3-12
IPB35N10S3L-26
RJK1051DPB
RJK1054DPB
MANUFACTURER
Vishay
Vishay
Infineon
Infineon
Renesas
Renesas
I_DS(MAX)
60A
25A
70A
35A
60A
92A
V_DS(MAX)
100V
100V
100V
100V
100V
100V
Transformer Selection
The LTC3300-2 is optimized to work with simple 2-wind-
ing transformers with a primary winding inductance of
between 1 and 20 microhenries, a 1:2 turns ratio (primary
to secondary), and the secondary winding paralleling up
to 12 cells. If a larger number of cells in the secondary
stack is desired for more efficient balancing, a transformer
with a higher turns ratio can be selected. For example, a
1:10 transformer would be optimized for up to 60 cells in
the secondary stack. In this case the external FETs would
need to be rated for a higher voltage (see above). In all
cases the saturation current of the transformer must be
selected to be higher than the peak currents seen in the
application.
See Table 8 for a list of transformers that are recommended
for use with the LTC3300-2.
Table 8
Snubber Design
Careful attention must be paid to any transient ringing
seen at the drain voltages of the primary and secondary
winding FETs in application. The peak of the ringing should
not approach and must not exceed the breakdown voltage
rating of the FETs chosen. Minimizing leakage inductance
present in the application and utilizing good board layout
techniques can help mitigate the amount of ringing. In
some applications, it may be necessary to place a series
resistor + capacitor snubber network in parallel with each
winding of the transformer. This network will typically
lower efficiency by a few percent, but will keep the FETs
in a safer operating region. Determining values for R and
C usually requires some trial-and-error optimization in the
application. For the transformers shown in Table 8, good
starting point values for the snubber network are 330Ω
in series with 100pF.
Boosted Gate Drive Component Selection
(BOOST = V_REG)
The external boost capacitor connected from BOOST⁺ to
BOOST^– supplies the gate drive voltage required for turning
on the external NMOS connected to G6P. This capacitor
is charged through the external Schottky diode from C6
to BOOST⁺ when the NMOS is off (G6P = BOOST^– = C5).
When the NMOS is to be turned on, the BOOST^– driver
switches the lower plate of the capacitor from C5 to C6,
and the BOOST⁺ voltage common modes up to one cell
voltage higher than C6. When the NMOS turns off again,
the BOOST^– driver switches the lower plate of the capaci-
tor back to C5 so that the boost capacitor is refreshed.
PART NUMBER
TURNS PRIMARY
MANUFACTURER RATIO* INDUCTANCE I_SAT
750312504 (SMT) Würth Electronics 1:1
3.5µH 10A
750312677 (THT) Würth Electronics 1:1
3.5µH 10A
MA5421-AL
Coilcraft
1:1
3.4µH 10A
CTX02-18892-R
Coiltronics
1:1
3.4µH 10A
XF0036-EP13S
XFMRS Inc
1:1
3µH
10A
LOO-3218
BH Electronics
1:1
3.4µH 10A
DHCP-X79-1001
TOKO
1:1
3.4µH 10A
C128057LF
GCI
1:1
3.4µH 10A
T10857-1
Inter Tech
1:1
3.4µH 10A
*All transformers listed in the table are 8-pin components and can be
configured with turns ratios of 1:1, 1:2, 2:1, or 2:2.
A good rule of thumb is to make the value of the boost
capacitor 100 times that of the input capacitance of the
NMOS at G6P. For most applications, a 0.1µF/10V capacitor
will suffice. The reverse breakdown of the Schottky diode
must only be greater than 6V. To prevent an excessive and
potentially damaging surge current from flowing in the
boosted gate drive components during initial connection of
the battery voltages to the LTC3300-2, it is recommended
to place a 6.8Ω resistor in series with the Schottky diode
as shown in Figure 3. The surge current must be limited
to 1A to avoid potential damage.
33002f
For more information www.linear.com/LTC3300-2
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