DEMO MANUAL
DC1721B-A/DC1721B-B
LTC4000EGN(-1)/LTC3789EGN
14.6V, 5A Battery Charger with
6V
IN
to 36V
IN
Buck-Boost Converter
DESCRIPTION
Demonstration circuit 1721B is a 14.6V, 5A battery charger
and PowerPath™ manager with 6V
IN
to 36V
IN
buck-boost
converter featuring the LTC4000/LTC3789, targeted at
4-cell LiFePO
4
applications. The output of this demo board
was specifically tailored for a Tenergy 10A-hour battery,
P/N 30207. Other voltages can be set by changing ROFB2
and RBFB2. The desired nominal voltage can be accurately
trimmed by using trim resistors R42 and R43. For example,
for 14.4V battery float voltage, change ROFB2 and RBFB2
to 86.6k, and add 7.5M at R42 and R43 for greater set
point accuracy.
This circuit was designed to demonstrate the high levels of
performance, efficiency, and small solution size attainable
using these ICs in a buck-boost converter battery charger,
intelligent PowerPath manager, and power supply. It oper-
ates at 400kHz and produces a regulated 5A/14.6V battery
charger output as well as a system output of up to 6.25A
from an input voltage range of 6V to 36V: suitable for a
wide variety of portable applications including instruments,
industrial equipment, power tools, and computers. It has
a total footprint area of 12.4cm
2
(3.6cm
2
for the LTC4000
circuit only). Synchronous rectification helps to attain
efficiency exceeding 96% at full load and nominal input.
DC1721B-A:
The LTC4000 has an input current limit/
regulation loop that prevents overloading sources with
limited output capability.
DC1721B-B:
The LTC4000-1 instead has an input voltage
regulation loop for Maximum Power Point (MPP) control.
MPP control extracts near maximum power from high
impedance sources such as solar panels, wind turbines,
or fuel cells.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
IN-MP1
I
IN2
V
FLOAT
I
BAT
V
OUT-SYS
I
OUT-SYS
F
SW
P
OUT
/P
IN
PARAMETER
Input Supply Range
Input Regulation Voltage
Input Current Limit
Battery Float Voltage
Output Regulation
Battery Charge Current
System Output Voltage
System Output Current Range
Switching (Clock) Frequency
Specifications are at T
A
= 25°C
MIN
6
TYP
11.85
11
14.4
14.6
±0.05
5.0
12.3
0
400
14.6
15.5
6.25
50
96.5
12.4cm
2
×
0.40cm
14.8
MAX
36
UNITS
V
V
A
V
%
A
V
A
kHz
mV
P-P
%
CONDITIONS
This Is the Input Voltage Lower Limit Set by the LTC4000-1
Line and Load (6V to 36V, 0A to 5A)
V
OUT-SYS P-P
System Output Ripple
Approximate Size
1
DC1721B-B (LTC4000-1) Only,
2
DC1721B-A (LTC4000) Only
V
IN
= 24V, I
OUT-SYS
= 5A (20MHz BW)
Component Area
×
Top Component Height
System Output Efficiency (See Figure 3) V
IN
= 24V, I
OUT-SYS
= 5A
dc1721bf
1
DEMO MANUAL
DC1721B-A/DC1721B-B
QUICK START PROCEDURE
Demonstration circuit 1721 is easy to set up to evaluate the
performance of the LTC4000/LTC3789. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
WARNING: BATTERIES ARE POTENTIALLY DANGER-
OUS HIGH ENERGY SOURCES. IMPROPER CON-
NECTION, OVERCHARGE, OR RAPID DISCHARGE
COULD RESULT IN EXPLOSION AND/OR FIRE.
NOTE. When measuring the output voltage ripple, care must
be taken to avoid a long ground lead on the oscilloscope
probe. Measure the output voltage ripple by touching the
probe tip and ground ring directly across the last output
capacitor as shown in Figure 1.
1. Set MODE jumper to CCM. Set CHARGE jumper to
DISABLE.
2. Set an input power supply that is capable of 6V to 36V
and 12A to 24V. Then turn off the supply.
3. With power off, connect the supply to the input terminals
VIN and GND.
NOTE.
a. Input voltages lower than 6V can keep the converter
from turning on due to the undervoltage lockout feature
of the LTC4000.
b. If efficiency measurements are desired, refer to Figure 1
for test setup.
4. Turn on the power at the input.
NOTE. Make sure that the input voltage never exceeds 36V.
5. Check for the proper VOUT-SYS of 15.3V. Turn off the
power at the input.
6. Once the proper output voltages are established, con-
nect a variable load capable of sinking 7A at 16V to the
output terminals VOUT-SYS and GND. Set the current
for 0A.
7. Turn on the power at the input.
NOTE. If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
8. Once the proper VOUT-SYS is again established, adjust
the load and/or source within the operating range and
observe the output voltage regulation, ripple voltage,
efficiency, input and output current limit, and other
desired parameters.
9. Turn off the power at the input.
10. Connect the output load and meters to the BAT output.
11. Set CHARGE jumper to ENABLE.
12. Turn on the power at the input.
13. Once the proper VOUT-SYS is again established, adjust
the load and/or source within the operating range and
observe the battery float voltage regulation and other
desired parameters.
14. Set the load to constant voltage mode to more easily
observe charge current and trickle charge current.
15.
(DC1721B-B 0NLY)
In order to observe MPP operation,
add a 0.25Ω to 0.3Ω, 10W resistor in series with the
DC source and set the source to 13V. Use a constant
voltage or constant resistance load characteristic. As
the load is increased, the input voltage will be regulated
at the MPP regulation point (11.75V) by reducing the
output of the DC/DC converter.
NOTE. Operation in the Instant-On region (V
OUT
< 12.5V)
may engage thermal limit circuit to protect Q7 in the linear
region.
NOTE. The optional thermal limit circuit for Q6 (Q9, RNTC3,
R55-59, and U4) is included to protect Q6 in case of an
extended short circuit on VOUT-SYS under adverse thermal
conditions (T
A
> 40°C). It may not be needed in applica-
tions with less severe thermal conditions, lower current
available to VOUT-SYS, or where continuous short-circuit
protection on VOUT-SYS is not required.
dc1721bf
2
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