LTC3305_15 Datasheet, PDF (23/28 Pages) Linear Technology – Lead-Acid Battery Balancer

LTC3305
Applications Information
When multiple LTC3305 devices are stacked, the logic out-
put pins may need to be level shifted and ground referred.
In Figure 9, optical isolators are used for level shifting.
Figure 11 shows an application in which an eight battery
stack is balanced using two LTC3305 devices and two
auxiliary cells. BAT1, BAT2, BAT3, and BAT4 are balanced
to each other using the lower LTC3305 whereas BAT5,
BAT6, BAT7, and BAT8 are balanced to each other by the
upper LTC3305.
PCB Considerations
In operation the LTC3305 can dissipate large amounts
of power which can increase die temperature and cause
the part to enter thermal shutdown. The exposed pad of
LTC3305 must be well soldered to the PCB to provide
adequate heat sinking. The exposed pad also provides an
electrical GND to the LTC3305.
The no-connect pin on the LTC3305 must be soldered to
a pad on the PCB and must be electrically isolated from
any other circuit node.
The trace that connects the AUXP pin to the positive
terminal of the auxiliary source must be as close to the
auxiliary source positive terminal as possible. Otherwise
the trace impedance adds to the ESR of the auxiliary cell
which manifests itself as an offset at the internal termina-
tion comparator.
The V1, V2, V3 and V4 traces must be Kelvin connected
directly to the battery terminal and must not share a com-
mon trace through which high balance current will flow.
Any voltage drop in these traces also manifests itself as
an offset voltage at the termination comparator input.
LTC3630A
BUCK REGULATOR
3.3V
100k EACH
MICROPROCESSOR
10nF
100nF
10nF
59k
93.1k
23.7k
10µF
25V
CM
V_REG
EN1
EN2
MODE
TERM1
TERM2
CP
BOOST
V4
UVFLT
V3
OVFLT
DONE
BAL
PTCFLT
BATX
BATY
V2
LTC3305
CTON
V1
CTOFF
CTBAT
9
NGATE1-9
V_L
V_H
AUXP
I_SET
AUXN
GND
ALL NMOS SWITCHES = SiR882DP
D1, D2 = CMMSH1-100
D2
249Ω
10µF
25V
1.33k
D1
10µF
25V
10µF
25V
10µF
25V
12.1k
NGATE5
12.1k
NGATE4
+
BAT4
6.04k
10k
NGATE3
R3 _BAT3 ⁺
12.1k 37.4k
NGATE2
R2 _BAT2 ⁺
10µF
25V NGATE6
12.1k
12.1k
NGATE7
R4
12.1k
12.1k 60.4k
NGATE1
R1 _BAT1 ⁺
PTC = PTGL13AROR8H2B71B0
10µF
+
AUX
25V
12.1k
NGATE8
12.1k
20k
NGATE9
R5
3305 F08
Figure 8. 4-Battery Application with External Resistors to Limit Power Dissipation
For more information www.linear.com/LTC3305
3305f
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