National Semiconductor
Application Note 1164
March 2001
LM3647 Reference Design
User’s Manual
GENERAL DESCRIPTION
application. The demo-board has extra components to
make it simple for the user to try out different batteries and
configurations. There are actually two different charge
current regulation methods and these are referred to as fast
and slow (LM317).
The LM3647 is a charge controller for Nickel-Cadmium
(Ni-Cd), Nickel-Metal Hydride (Ni-MH) or Lithium-Ion (Li-Ion)
batteries. The device uses a pulsed-current charging or a
constant-current charging technique. The device can also be
configured to discharge before charging. Throughout the
charging sequence the LM3647 monitors voltage and/or
temperature and time in order to terminate charging.
JUMPER SETTINGS
J5
VCC
Type Select
•
•
•
•
•
Negative delta voltage (−∆V)
Maximum voltage
Ni-MH
Ni-Cd
Li-Ion
GND
Hi-Z
Optional: Delta temperature/delta time (∆T/∆t)
Optional: Maximum temperature
Backup: Maximum time
J2
VCC
GND
Hi-Z
Charge Mode
No discharge
The LM3647 is user configurable for three battery
chemistries: Ni-Cd, Ni-MH or Li-Ion.
Maintenance charge only
Discharge before charge
In Ni-Cd/Ni-MH mode, four different charging phases are
used:
J2
VCC
GND
Maintenance Mode
•
•
•
•
Softstart charge
Fast charge
Charge indefinitely
No charge and restart fast-charge if battery
becomes discharged
Topping charge
Maintenance charge
Hi-Z
Charge indifinitely and restart fast-charge if
battery becomes discharged
In Li-Ion mode, four different charging stages are used:
•
•
•
•
Qualification
Fast Charge Phase 1, Constant Current
Fast Charge phase 2, Constant Voltage
Maintenance charge
Regulation Method / Cell
J5
J6
J7
Voltage
VCC
VCC Fast LM3647 controls charge current
GND Slow External (LM317) charge control
KEY FEATURES
GND VCC Fast LM3647 controls charge current
GND Slow External (LM317) charge control
•
•
Auto-adaptive fast charge
High-resolution, accurate voltage monitoring prevents
Li-Ion under-charge or overcharge
Hi-Z VCC Fast 4.2V/Cell Li-Ion
GND Fast 4.1V/Cell Li-Ion
•
Fast charge, pre-charge and maintenance currents are
provided. Different currents are selectable via external
resistors
Timeout
Timeout settings J18 (set according to charge-rate C), See
Section 3.0 for more information.
•
•
•
•
•
•
Fast-charge termination by temperature/time, maximum
voltage, maximum temperature and maximum time
Temperature Input
Dynamically detects battery insertion, removal, short
circuit and bad battery without additional hardware
The optional Temperature input is connected to J3 and if not
used Short J8.
Supports charging of battery packs with 2-8 cells of
Ni-Cd, Ni-MH or 1-4 cells of Li-Ion
Voltage Regulation Range
Three LED indicators and one Buzzer output indicate
operational modes
Voltage regulation loop setting J14 (not used with external
LM317 regulation I.e. J7 = slow), defines maximum voltage
output. See also Section 3.0 LM3647 REFERENCE
DESIGN DEMO-BOARD.
Ni-MH/Ni-Cd charge mode, Li-Ion charge mode or
discharge mode can be selected manually
PWM switching controller
Voltage Measurement
DOCUMENTATION INFORMATION
The battery voltage is selected with the Voltage jumpers J11
& J12 depending on number of cells/chemistry. For instance,
a 9V Ni-Cd block battery has 6 cells in it and therefore needs
the jumper at ″Ni 6-Cells″ on J11 and J12:
The following documentation describes how to use the
LM3647 demo-board and also gives a few tips on design
calculations. Please note that not all components on the
demo-board are used when designing
a
charger
© 2001 National Semiconductor Corporation
AN101315
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and the charge process will restart. This occurs only with
batteries that are already fully charged, and consequently
should not be recharged. If the battery voltage has not
plyRejectionRatio), because they are both powered
directly from the unregulated DC-input. U1 must also
have enough current drive to control the transistor Q3. U2
should preferably have a low input offset, since this error
will be amplified.
>
reached the Li-Ion battery qualification voltage (CEL-pin
1.2V) within 1 minute of the Qualification Phase, the battery
is considered to be defective, and the charger goes into error
•
•
The regulator IC2 criteria is that it has to be able to
handle the input DC-voltage, and deliver enough current
to drive the circuitry (all LED’s, buzzer, LM3647).
<
mode. It stays there until the battery is removed (CEL-pin
1.0V).
The next phase is Fast Charge Constant Current. During this
phase the current is constant, and the battery voltage will
slowly rise (due to the charging). When the battery has
reached its maximum battery voltage (CEL at 2.675V or
2.74V, depending on SEL3, it will go to the next phase which
is Fast Charge Constant Voltage.
The transistor Q3 must be able to handle the charge
current and (depending on charge current) must be
provided with an adequate heatsink.
•
•
The transistor Q2 must be able to handle the maximum
discharge current.
The Diode D1 must be able to handle the maximum
charge current.
During this phase, the charger will keep the voltage constant
and stay in this phase until the current has decreased to a
threshold value (CS at 2.3V).
1.2.2.2 Clarifications Regarding Circuit Schematics
The battery is now fully charged, and the charger can
behave in different modes, depending on SEL1. It can either
maintenance charge the battery and restart the charge
process if the battery voltage drops below the maintenance
The circuitry with Q4, R26 and R27 (see section below) is
used to protect the battery from excessive charge current.
When the current flows through the current sense resistor
R9, and is amplified by U2, the voltage at U2’s output drops
from 2.5V until Q4 starts conducting. It discharges the
RC-network that generates the DC-voltage from the
PWM-output of the LM3647.
<
restart threshold value (CEL 2.153V), or just maintenance
charge the battery and don’t restart the charge process if the
battery becomes discharged. The last mode is no
maintenance charge, and restarts the charge process if the
battery voltage drops below the maintenance restart
1.2.2.3 Setting The Charge Timeout
<
threshold value (CEL 2.153V).
The LM3647 uses the charge timeout value as a backup
termination method if the normal termination methods fail.
The charge timeout also controls the length of some of the
phases like the Topping Charge phase (Ni-Cd/Ni-MH). The
timeout is selectable from a charge rate of 3.2C to 0.4C. The
table below shows which values will result in a certain
timeout.
1.2.2.1 Components Critical to Total Charger
Performance
•
The capacitance C2 connected to CEXT must be of a
type that has low internal resistance, low loss, high
stability and low dielectric absorption. The capacitance
mounted on the Demo Board is a metallized polyester
type from WIMA, 2220 series.
•
The operational amplifiers U1 and U2 must be capable of
rail-to-rail output, and have a high PSRR (PowerSup-
TABLE 1. Charge Timeouts
Ni-Cd/Ni-MH
Ni-Cd/Ni-MH
Li-lon CC
(minutes)
Li-lon CV
(minutes)
Appropriate
R Value
C Value
Fast Charge
(minutes)
75
Topping (minutes)
Charge Rates
100 kΩ
100 kΩ
100 kΩ
100 kΩ
100 kΩ
100 kΩ
100 kΩ
100 kΩ
0 nF
10 nF
15 nF
22 nF
33 nF
47 nF
68 nF
100 nF
20
25
50
75
3.2C
2.4C
1.4C
1.2C
0.9C
0.7C
0.5C
0.4C
100
70
100
160
190
260
330
450
540
160
40
110
130
170
220
300
360
190
50
260
65
330
80
450
115
135
540
EXAMPLE 1:
AN101315-18
3
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@
The actual timeouts (with RCIN 2.5 MHz) is:
Phase
Timeout
∼ 330 Minutes
∼ 80 Minutes
Fast Charge
Topping Charge
EXAMPLE 2:
AN101315-19
@
The actual timeouts (with RCIN 2.5 MHz) is:
Phase
Timeout
Fast Charge Constant Current
− 130 Minutes
− 190 Minutes
Topping Charge Constant Voltage
1.2.2.4 Setting The Charge Current
1.2.2.5 Setting Maximum Battery Voltage
The charge-current is selected by setting the current sensing
resistor and the gain of the differential amplification stage.
The current sensing resistor (R5) should be dimensioned
such that the voltage drop over it is not too small, since the
signal will be more susceptible to noise and offsets in the
amplification-stage. The resistance should not be too large
either (especially in high-current applications), because this
will only generate more heat from the component. A suitable
value is one where 50 mV dropped across the resistor when
maximum current flows through it. The differential signal is
then amplified, inverted and centered around the 2.5V
reference by the operational amplifier and fed to the CS pin
on the LM3647. The gain must be dimensioned by setting
the appropriate ratio between R1 (R2) and R3 (R4). The
figure below is dimensioned for a maximum current of about
1.1A. This was dimensioned using the following formula:
The resistor network (see the figure below) scales the
battery voltage to a suitable level for the LM3647. For
Ni-Cd/Ni-MH batteries the network is less critical, but limits
the maximum battery voltage, it is only used as a backup
termination method. For Li-Ion batteries the network must be
more accurate, requiring precision resistors with low
tolerances.
•
For Ni-Cd/Ni-MH:
The dimensioning is accomplished in the following manner:
First calculate the maximum battery voltage for the specific
battery pack. See example below.
→
BatteryVoltage/Cell = 1.2V NumberOfCells = 5
PackVoltage = 1.2x5 = 6V
Battery-
→
MaximumBatteryVoltage/Cell = 1.85V
MaximumBattery-
Voltage = 1.85x5 = 9.25V
When the Maximum Battery Voltage has been determined,
the voltage divider network has to be dimensioned using the
following formula:
AN101315-3
AN101315-2
AN101315-4
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•
For Li-Ion:
Charge Phase:
Soft Start
Duty Cycle:
10%
The voltage divider network for Li-Ion is very important. If the
battery voltage is scaled too low, the battery will not attain its
full capacity when charged, and if scaled too high, the
battery may become damaged. Never exceed the
recommended maximum voltage or current for a Li-Ion
battery!
Fast Charge
100%
10%
Topping Charge
Maintenance Charge
5%
The dimensioning is done in the following manner.
First calculate the maximum battery voltage for the specific
battery pack. See example below.
→
BatteryVoltage/Cell = 3.6V NumberOfCells = 2
PackVoltage = 3.6x2 = 7.2V
Battery-
→
MaximumBatteryVoltage/Cell = 4.1V
MaximumBattery-
Voltage = 4.1x2 = 8.2V
When the maximum battery voltage has been determined,
the voltage divider network has to be dimensioned using the
following formula:
The LM3647 has two different regulation voltages, which the
user can select. These are 2.675V (SEL3 tied to GND) and
2.740V (SEL3 tied to VCC). This selection pin can be used to
configure the charger to regulate for different input voltages
so that the charger can handle both 3.6V- and 3.7V-cells,
without changing the resistor values in the divider network.
SEL3 can also be used if there is problem in finding the right
values in the resistor network. The recommended tolerance
of the resistors are 0.1%, but 1% may be used with a
marginal loss of battery capacity by subtracting the tolerance
of the divider network from the maximum battery voltage.
•
Using the LM3647 without current feedback, for
Ni-Cd/Ni-MH only (slow PWM mode):
This mode uses an external constant-current power-source,
which is switched on and off according to the charge-phase
of the LM3647. The frequency is approximately 0.1 Hz. The
advantage of this charge method is that operational
amplifiers and the current feedback circuitry are not needed,
which provides a low-cost solution. The dimensioning of the
voltage divider network is performed the same way. The
constant current source is dimensioned in the following
manner:
AN101315-7
The LM3647 regulates the constant current source by
turning the transistor Q1 on and off.
When the transistor is off, the LM317T regulator feeds a
constant current to the battery (at V_OUT).
When the transistor is on, the output from the LM317 is
limited to 1.25V (which should be greater than the battery
voltage).
5
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2.0 APPLICATION INFORMATION
2.1 Typical Example
2.1.1 Ni-Cd/Ni-MH
AN101315-8
Set To:
VCC
SEL1
SEL2
Ni-MH
SEL3
No Discharge before Charge
Discharge before Charge
Maintenance Charge Only
Fast-PWM (LM3647 has current feedback)
NA
Hi-Z
NA
GND
Ni-Cd
Slow-PWM (external current control)
6
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2.1.2 Li-Ion
AN101315-9
Set To:
VCC
SEL1
SEL2
SEL3
After charging, maintenance charging until battery removal.
NA
4.2V/Cell
Hi-Z
After charging, maintenance charging until battery removal. If battery
voltage drops below a predefined value, the charger restarts the
charge-process.
Li-Ion
NA
GND
After charging, no maintenance charging is applied. If battery voltage
drops below a predefined value, the charger restarts the charge-process.
NA
4.1V/Cell
Note: When a three chemistry charger is designed, special considerations must be taken into account regarding configuration pin SEL3. this pin has differnet
meanings when switching between Ni-Cd/Ni-MH and Li-Ion. To ensure correct operation, the SEL3-pin MUST be tied to VCC. If Li-Ion cells of 4.1V/Cells is
used, then minor adjustments have to be done to the voltage measurement resistor divider.
7
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3.0 LM3647 REFERENCE DESIGN DEMO-BOARD
The demo-board provides combined multi-chemistry
a
The upper values correspond to a current sense resistor of
0.047Ω while the lower correspond to 0.100Ω (see previous
figure).
solution with hardware for both external constant current
source and LM3647 controlled charge current. Located near
the top-left corner of the board is the power supply connector
(next to the heatsink). When using the external constant
current source, a power resistor needs to be connected at
the connector marked 317-resistor. The values of the resistor
can be calculated using the equation 4 mentioned earlier.
At the bottom-right corner of the board are two connectors
that lead to the battery and discharge resistor. The value of
the discharge resistor depends on the battery pack voltage
and the maximum discharge rate. The demo-board has
different jumpers that are assigned to different setups. Some
of the components are not populated, providing support for
user-specific values.
AN101315-13
The battery voltage is selected with the Voltage jumpers J11
and J12 (see below for settings).
The timeout jumper J18 is used to select different timeouts
from 2.4C to 0.4C. The values mounted on the demo-board
result in timeouts corresponding to the charge-rates shown
below:
AN101315-14
The jumper J3 is used to connect to an optional
NTC-resistor. If no temperature sensor is used, the jumper
J8 must be shorted. The Demo-board was designed for an
NTC thermistor from Siemens (B57861S302F40) with the
AN101315-10
The PWM jumper J7 is used to connect the PWM-signal to
either the external constant current source (marked slow) or
the RC-filter that is connected to the operational amplifier
(marked fast).
@
following specifications: 3kΩ
25˚C, β = 3988. If an NTC
with different characteristics is used, then the resistor R28
may need to be changed. The charger uses voltage levels to
trigger under/over temperature conditions. The voltage at the
temperature-input must be between 2.2V or 0.5V for the
charger to start. During charging the voltage must stay
between 3.0V for Li-Ion, or 3.15V for Ni-Cd/Ni-MH, and 0.5V
or the charger will register a temperature fault and abort the
charge.
The PWM-FB jumper J14 is used to select different
amplification levels of the PWM signal. The jumper with the
battery voltage ranges are shown below:
AN101315-11
AN101315-15
The I jumper J10 is used to select between different current
sense resistors. The values mounted are 0.047Ω and
0.100Ω.
AN101315-12
The different current sense voltage amplification level is
selected via CURRENT jumpers J9 and J13 (both jumpers
must be changed in pairs, see figure below).
AN101315-16
The three jumpers J2, J5 and J6 are connected to the three
selection-pins SEL1, SEL2 and SEL3. These jumpers are
used to select how the charger should behave (see Charger
Modes table).
8
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AN101315-17
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