QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B
LTC4011
DESCRIPTION
Demonstration circuit DC674B is a complete Fast Bat-
tery Charger capable of charging 3, 4, 8 or 10 series
connected NiMH or NiCd cells. Other cell counts can
also be charged (up to 16 cells) by installing an appro-
priate resistor on the board.
The power portion of the circuit consists of a 550kHz
synchronous step-down constant current source which
provides 2A of charge current. Other charge currents
can be selected by changing the sense resistor value,
and for higher charge current (2 to 4A), the PC board
has a dual layout for the top switch to allow a larger
FET to be used. A PowerPath™ FET is also included that
provides a low voltage drop path between the battery
and an external system load when the input power is
removed
Charge termination includes -ΔV, ΔT/Δt, peak voltage
and a safety timer. The thermistor function is set by the
NTC jumper, JP1. Battery chemistry is set by the CHEM
jumper, JP2. The number of series cells is set by the
CELLS jumper, J1. Finally, the safety timer length is set
by the TIME jumper, J2. Four LEDs indicate charger
ready, top-off charge, charging, and FAULT status.
Design files for this circuit board are available. Call
the LTC factory.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Power-
Path is a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
STANDALONE NIMH/NICD BATTERY CHARGER BOARD
Performance Summary
PARAMETER
Minimum Input Voltage
T
A
= 25°C
VALUE
6.3V
8.3V
12.3V
20.3V
n
∙
2.0V + 0.3V
25V
2A ± 8%
−20mV ± 2mV
−10mV ± 1.5mV
2°C/min ± 0.16°C Temperature Rise
1°C/min ± 0.14°C Temperature Rise
400mA ± 80mA
200mA ± 50mA
CONDITIONS / NOTES
3 series cells (Default)
4 series cells
6 series cells
10 series cells
n series cells
Limited by Input Capacitor Volt Ratings.
CHEM=NiCd
CHEM=NiMH
CHEM=NiCd
CHEM=NiMH
350mV < VCELL < 900mV
CHEM=NiMH, ΔT/Δt Termination Only
Maximum Input Voltage
Maximum Charge Current
−ΔV Termination
ΔT/Δt Termination
Precharge Current
Top Off Charge Current
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B
STANDALONE NIMH/NICD BATTERY CHARGER BOARD
QUICK START PROCEDURE
Demonstration circuit 674B is easy to set up to eva-
luate the performance of the LTC4011. Refer to Fig-
ure 1 for proper measurement equipment setup and
follow the procedure below.
1. Set the jumpers according to the type and specifi-
cations of the pack under evaluation.
2. With all power off, connect input power supply,
and meters as shown in Figure 1.
3. Preset the system load to 0A and the input
supply to 0V, 0A current limit.
4. Turn on the supplies, setting the current limit to
2A.
5. Adjust the input voltage to the desired value, up
to 25V.
6. Connect the battery to begin charging.
2. To use a system load up to 1A in parallel with
the charging circuit, connect to SYSTEM LOAD.
Adjust load and input supply current limit as
necessary.
3. For external thermistor connection, set jumper
JP1 to BAT. For the on-board thermistor, set JP1
to BRD. To remove the thermistor from the circuit,
set JP1 to OUT.
4. For custom cell count, set jumper J1 to XCELLS
and install R14 with the appropriate value.
5. For alternative timer settings, set jumper J2 as
necessary. For custom timer settings, set J2 to
4.3Hr and install R23 with the appropriate val-
ue.
Note:
This value also affects Precharge and TOC
times as well.
6. To measure the average voltage per cell, connect a
meter to VCELL.
7. To pause the charge cycle, connect a lead from
PAUSE to GND.
Note:
This pauses the timer as well, but status
outputs remain active.
Optional
1. To use a battery with a 5-pin blade connector,
use J3.
Please refer to the LTC4011 datasheet for additional information.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B
STANDALONE NIMH/NICD BATTERY CHARGER BOARD
2A
A
+
BATTERY
…
−
10k NTC
−
VIN
−
+
V
+
*Locate
close to
battery
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B
STANDALONE NIMH/NICD BATTERY CHARGER BOARD
CHARGING NIMH/NICD BATTERIES
Nickel based batteries are typically charged by a
constant current source, allowing the battery vol-
tage to rise to the level it requires (within limits)
to force this current. When batteries are fast
charged (1 to 2 hours) the charge cycle must be
terminated when the battery reaches full charge.
Detecting when the battery is fully charged is
usually done by one or more methods.
1. –∆V method: Measures the battery voltage
as it is being charged with a constant current.
The voltage will rise as the battery accepts
charge. When it approaches full charge, the
battery voltage will begin rising faster, reach a
peak then begin to drop. When the battery vol-
tage drops a fixed amount of mV (depending on
battery chemistry), the battery is fully charged
and the charge cycle terminates.
2.
∆T/∆t
method: Measures the rate of tempera-
ture rise vs. time. During a fast charge, the bat-
tery temperature begins to rise. When it ap-
proaches full charge, the battery temperature
will begin to rise quickly. When the rate of tem-
perature rise reaches a fixed number of
°C/minute (depending on battery chemistry) the
charge cycle terminates. NiMH batteries add a
top-off charge that continues charging at a low-
er current until the timer ends the charge cycle.
For either of these termination methods to work
correctly, the charge current must be pro-
grammed to a sufficiently high current level.
LTC recommends between C/2 and 2C rates,
but charging at 2C may result in excessive cell
temperature, especially for small, low capacity
NiMH cells. Rates lower than C/2 will be too dif-
ficult to detect for LTC4011 termination algo-
rithm.
“C rate” is a measure of cell capacity in mAHr.
For example, to charge an 1800mAHr battery at
1C would require a charge current of 1.8A.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC674B
STANDALONE NIMH/NICD BATTERY CHARGER BOARD
DIFFERENCES BETWEEN NICD & NIMH BATTERIES
NiCd batteries exhibit very little temperature rise
during most of the charge cycle. The tempera-
ture rise mainly occurs near the end of the
charge cycle.
Whereas, NiMH battery temperature rise occurs
throughout the charge cycle and accelerates
near the end of the charge cycle.
The -∆V that occurs when charging a NiMH bat-
tery is less than a NiCd. This makes -∆V termina-
tion somewhat more difficult to detect for a NiMH
battery, therefore it is also recommended to in-
clude a thermistor in the NiMH battery packs.
Figure 2. NiMH Charge Profile (1C Charge Rate)
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