DEMO MANUAL DC2043B
LTC3305EFE
Lead Acid Battery Balancer
DESCRIPTION
Demonstration circuit 2043B is a lead-acid battery balancer
featuring the
LTC
®
3305.
The LTC3305 balances up to four
lead-acid batteries connected in series and incorporates all
voltage monitoring, gate drive and fault detection circuitry.
The LTC3305 employs an auxiliary battery or an alternative
storage means to transfer charge to or from each individual
battery within the stack. There are two operating modes,
TIMER mode and CONTINUOUS mode, selected by the
MODE pin. In TIMER mode, once the balancing operation
is complete, the LTC3305 goes to a low power state for
a programmed time and then periodically rebalances the
batteries. In CONTINUOUS mode, the balancing operation
continues even after the batteries are balanced to their
programmed termination voltage.
The LTC3305EFE is available in a 7mm
×
7mm 38-lead
TSSOP surface mount package with exposed pad.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2043B
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog
Devices, Inc. All other trademarks are the property of their respective owners.
BOARD PHOTO
Figure 1. DC2043B Demo Board
Figure 2. Thermal Image of DC2043B
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1
DEMO MANUAL DC2043B
PERFORMANCE SUMMARY
SYMBOL
V
BAT
V
TERMINATE
V
TERMINATE
V
TERMINATE
V
TERMINATE
V
REG
PARAMETER
Battery Voltage Range
Termination Voltage Range
Termination Voltage Range
Termination Voltage Range
Termination Voltage Range
Regulator Output Voltage Range
TERM2 = 0, TERM1 = 0
TERM2 = 0, TERM1 = 1
TERM2 = 1, TERM1 = 0
TERM2 = 1, TERM1 = 1
I
VREG
= 200µA
Specifications are at T
A
= 25°C
CONDITIONS
MIN
4.0
±5
±17.5
±42.5
±90
2.4
to
to
to
to
to
to
MAX
16.0
±20
±32.5
±57.5
±110
2.6
UNITS
V
mV
mV
mV
mV
V
OPERATING PRINCIPLE
Refer to the block diagram within the LTC3305 data sheet
for its operating principle.
The LTC3305 balances batteries using an auxiliary battery
or an alternate storage means as a charge reservoir. The
LTC3305 controls external N Channel MOSFET switches
in a preprogrammed sequence to connect a battery in
the stack to the auxiliary battery. Charge is transferred
to or from the auxiliary battery when it is connected to a
battery in the stack.
The LTC3305 can operate in one of two modes, TIMER
mode or CONTINUOUS mode, programmable via the
MODE pin. Balancing operation begins once the CBOOST
capacitor is charged to at least 6.95V. The EN1 and EN2
pins select the number of batteries in the stack.
EN1
0
0
1
1
EN2
0
1
0
1
Application
SHUTDOWN
2 Battery Stack
3 Battery Stack
4 Battery Stack
voltage difference between the auxiliary battery and BAT1
is less than the selected termination voltage, the battery
is deemed to be in a balance state with respect to the
auxiliary battery. The bottom switches will be turned off
and the next battery within the stack will be connected.
If the voltage difference between the auxiliary battery and
BAT1 is greater than the selected termination voltage, the
top switches that connect the positive terminal of BAT1
to the auxiliary battery’s positive terminals through the
PTC thermistor are turned on. Current is limited by the
PTC thermistor. Figure 3 shows the startup battery current
where the PTC is limiting as it heats up. Figure 4 is the
steady state battery current after the PTC has reached its
thermal equilibrium. After a 50ms delay, the termination-
sense comparator starts to monitor the voltage across the
auxiliary battery and the battery. The battery will remain
connected to the auxiliary battery until the voltage differ-
ence decreases to the selected termination voltage or a
t
BAT
timeout occurs.
At this point all switches are turned off and the second
battery in the stack will be connected to the auxiliary bat-
tery after a 50ms delay. This 50ms delay provides a break-
before-make function before the next battery is connected.
The cycle will be repeated for each battery in the stack.
Once all batteries in the stack are balanced the
DONE
pin is
pulled low, the
BAL
pin is in its high state and the LTC3305
is put into a low power off state. The stack is deemed bal-
anced when for a four battery stack, the termination-sense
comparator detects V
TERMINATE
on five consecutive cycles
that connect each of the batteries to the auxiliary battery
using the bottom switches only.
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With the MODE pin set to 0 the LTC3305 will operate in
the TIMER Mode. The
BAL
pin will be pulled low, indicating
that the part is enabled and balancing the battery stack.
The balancing operation begins with the terminal of the
auxiliary battery connected to the negative terminal of BAT1,
the lowest battery in the stack. The bottom switches that
connect the negative terminals of BAT1 to the auxiliary
battery's negative terminal are turned on. After a 50ms
delay, the voltages across the auxiliary battery and BAT1
are compared by the termination sense comparator. If the
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DEMO MANUAL DC2043B
OPERATING PRINCIPLE
BATX
5.00V/DIV
BATY
5.00V/DIV
1. There are no ON or OFF states. The balancing operation
continues even if the stack is in balance. The balanc-
ing operation is terminated only if the part is put into
shutdown. The
BAL
pin is always pulled low.
2. In CONTINUOUS mode, the top switches are turned
on and balancing operation on a battery is terminated
by the t
BAT
time out. Since the auxiliary cell remains
connected to the battery until a t
BAT
time out, its volt-
age can change before it connects to the next battery
in the stack. As a result, when the stack is balanced
and the DONE pin is pulled low, the voltages across
individual batteries in the stack may differ by more than
the programmed V
TERMINATE
. In the worst case, when
the capacity of the auxiliary cell is much smaller than
the battery, the individual battery voltages will differ by
twice the programmed V
TERMINATE
when balanced.
The LTC3305 provides undervoltage and overvoltage
threshold detection that can be programmed using
resistors that are connected between the I
SET
, VL and
VH pins and ground. The voltages set on VL and VH are
scaled by a factor of 10, setting the battery undervoltage
and overvoltage thresholds, respectively.
When an undervoltage or overvoltage fault condition is
detected, the corresponding
UVFLT
or
OVFLT
pin is pulled
low. The balancing operation is not interrupted during this
time. If the fault condition goes away during balancing, the
corresponding fault pin is put into its high impedance state.
A number of components are included on the DC2043B
to protect the circuit from damage when hot-plugging the
battery connections to the board.
Clamping diode D100 prevents the BOOST pin on the
LTC3305 from going excessively negative with respect
to the V4 pin during hot plug. Likewise, D101 prevents
the voltage at the CP pin from going excessively negative
with respect to the CP pin.
Antiparallel Schottky diodes and a 100Ω resistor tie each
power connection with its corresponding sense (Kelvin)
connection. The resistor keeps the potential between the
power and sense connections near zero while the diodes
maintain the voltage difference to a few tenths of a volt
even when transient currents want to flow between power
and sense connections.
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AUX BATTERY
CURRENT
200mA/DIV
2.0s/DIV
dc2043 F03
Figure 3. Start-Up Battery Balancing Current
BATX
5.00V/DIV
BATY
5.00V/DIV
AUX BATTERY
CURRENT
200mA/DIV
2.0s/DIV
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Figure 4. Steady State Battery Balancing Current
In TIMER mode, the balancing operation continues for a
maximum of the programmed t
ON
time. After the t
ON
time,
LTC3305 is put into a low power off state for a programmed
t
OFF
time, even though the batteries may not be balanced.
Once the t
OFF
time expires, the LTC3305 is put into the
ON state, and normal operation resumes. The
BAL
pin is
in its high impedance state if the part is in the OFF state
or when the part is in shutdown.
With the MODE pin set to 1, the LTC3305 will operate in the
CONTINUOUS Mode. The part functions in much the same
way as in the TIMER mode with the following differences.
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DEMO MANUAL DC2043B
OPERATING PRINCIPLE
During some hot-plug events, the gate-to-source voltage
on some of the power FETs can approach the maximum
VGS rating of the FETs. Back-to-back Zener diodes (15V
nominal threshold) are included across all power-FET
gate-source pins.
Inrush current between the sense connections and capaci-
tors C6, C12–C15 is limited by resistors R107–R111. These
resistors are pulse-power-rated. The higher pulse-power
capability is a necessary requirement for these resistors.
These resistors are 5Ω, 1206 except for the resistor in
the BAT4_KF net which is 2Ω, 1206 because, while it
senses the voltage at the top of the battery stack, it also
sinks a small amount of current to power the internals of
the LTC3305.
TVS diodes D135 to D138 are listed as “OPT” on the sche-
matic, and are not included on the DC2043B. However, a
transient-voltage-suppressor diode is included across
the battery stack to protect the LTC3305 from transients
generated during hot plugging. The threshold voltage of
the part is specified to lie between 66.7V and 73.7V.
Fuses are present on each of the 14 connections to external
batteries. Seven power connections employ a 7A-rated
fuse. The sense connections (XXX_K) use 1A fuses. Note
that the protection circuits described above are placed on
the internal-to-the-board side of the fuses. This placement
ensures isolation and disconnection of the protection
circuits in the event of a steady-state fault condition.
QUICK START PROCEDURE
Using short twisted pair leads for any power connections,
with all loads and power supplies off, refer to Figure 5 for
the proper measurement and equipment setup.
Follow the procedure below:
1. Before connecting PS1-PS5 to the DC2043B, the power
supplies must have its current limit set to 5A . For
most power supplies with a current-limit-adjustment
feature the procedure to set the current limit is as
follows. Turn the voltage and current adjustment to
minimum. Short the output terminals and turn the
voltage adjustment to maximum. Adjust the current
limit to 5A for PS1. Turn the voltage adjustment to
minimum and remove the short between the output
terminals. Repeat for PS2-PS5 The power supplies
are now current limited to 5A .
a. Initial Jumper and PS settings:
JP1(MODE)
= CONT
JP2 (EN)
= SD
JP3(TERM1)
= 1
JP4 (TERM2)
= 1
PS1
= Off
PS2
= Off
PS3
= OFF
PS4
= Off
PS5
= Off
PS6
= Off
2. Connect power supplies, load resistors and me-
ters as shown in Figure 5. Turn on PS1 and slowly
increase voltage to 2.0V while monitoring the input
current. If the current remains less than 200mA,
increase PS1 to 12.0V. Repeat for PS2-PS4.
3. Turn on PS5 and slowly increase voltage to 2.0V while
monitoring the input current. If the current remains less
than 200mA, increase PS5 to 11.8V. Turn on PS6 and
slowly increase voltage to 2.0V while monitoring the
input current. If the current remains less than 20mA,
increase PS6 to 5.0V.
4. Measure the voltage from the VREG turret to ground.
The voltage should read approximately 2.6V. Measure
the voltage from the BOOST test point to V4. The volt-
age should read approximately 0V. No LED should be
on.
5. Set JP2 to EN. Measure the voltage from the BOOST
test point to V4. The voltage should read approximately
8.5V.
6. Measure the voltage from the I
SET
test point to ground.
The voltage should read approximately 1.2V.
4
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DEMO MANUAL DC2043B
QUICK START PROCEDURE
7. Measure the voltage from the VH test point to ground.
The voltage should read approximately 1.52V.
8. Measure the voltage from the VL test point to ground.
The voltage should read approximately 0.95V.
9. With JP1 set to CONT, JP2 set to EN, JP3 set to 1 and
JP4 set to 1, observe that the BATX and BATY LEDs
are cycling through their four states.
BATX
LED
OFF
OFF
ON
ON
BATY
LED
OFF
ON
ON
OFF
Active
Battery
BAT1
BAT2
BAT3
BAT4
10. Decrease PS1 and PS5 to 9.4V and observe that while
the BATX and BATY are off, the
UVFLT
LED is on.
11. Increase PS1 and PS5 to 15.9V and observe that
while the BATX and BATY are off, the
OVFLT
LED is
on. Decrease PS1 and PS2 to 12.0V.
12. Decrease PS2 to 11.5V. Set JP1 to TIMER. Observe
that the BATX LED is off and BATY LED is on the ma-
jority of the time. Increase PS2 to 12V and observe
that the balancing action stops. The BAL LED will be
off and the DONE LED will be on.
13. Set JP1 to CONT and JP2 to SD. Set PS5 to 11.8V.
Observe that balancing action has stopped and no
LEDs are on. Set JP2 to EN and observe that balancing
action starts.
14. Turn off all power supplies.
10
25W
+
PS5
+
PS6
10
25W
+
PS4
10
25W
+
PS3
10
25W
+
PS2
+
PS1
5
50W
Figure 5. Proper Measurement Equipment Set-Up
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