National Instruments LM3647 User Manual

LM3647 Reference Design
User’s Manual

LM3647 Reference Design User’s Manual AN-1164

National Semiconductor
Application Note 1164
March 2001

GENERAL DESCRIPTION

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.

Negative delta voltage (−∆V)

•

Maximum voltage

•

Optional: Delta temperature/delta time (∆T/∆t)

•

Optional: Maximum temperature

•

Backup: Maximum time

•

The LM3647 is user configurable for three battery
chemistries: Ni-Cd, Ni-MH or Li-Ion.

In Ni-Cd/Ni-MH mode, four different charging phases are
used:

Softstart charge

•

Fast charge

•

Topping charge

•

Maintenance charge

•

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

•

KEY FEATURES

Auto-adaptive fast charge

•

High-resolution, accurate voltage monitoring prevents

•

Li-Ion under-charge or overcharge
Fast charge, pre-charge and maintenance currents are

•

provided. Different currents are selectable via external
resistors

Fast-charge termination by temperature/time, maximum

•

voltage, maximum temperature and maximum time
Dynamically detects battery insertion, removal, short

•

circuit and bad battery without additional hardware
Supports charging of battery packs with 2-8 cells of

•

Ni-Cd, Ni-MH or 1-4 cells of Li-Ion
Three LED indicators and one Buzzer output indicate

•

operational modes
Ni-MH/Ni-Cd charge mode, Li-Ion charge mode or

•

discharge mode can be selected manually
PWM switching controller

•

DOCUMENTATION INFORMATION

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

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).

JUMPER SETTINGS

J5 Type Select

V

CC

GND Ni-Cd
Hi-Z Li-Ion

V

CC

GND Maintenance charge only
Hi-Z Discharge before charge

J2 Maintenance Mode

V

CC

GND No charge and restart fast-charge if battery

Hi-Z Charge indifinitely and restart fast-charge if

J5 J6 J7

V

CCVCC

GND V

Hi-Z V

Timeout

Timeout settings J18 (set according to charge-rate C), See
Section 3.0 for more information.

Temperature Input

The optional Temperature input is connected to J3 and if not
used Short J8.

Voltage Regulation Range

Voltage regulation loop setting J14 (not used with external
LM317 regulation I.e. J7 = slow), defines maximum voltage
output. See also Section

DESIGN DEMO-BOARD

Voltage Measurement

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:

Ni-MH

J2 Charge Mode

No discharge

Charge indefinitely

becomes discharged

battery becomes discharged

Regulation Method / Cell

Voltage

Fast

LM3647 controls charge current

GND

Slow

External (LM317) charge control

Fast

CC

GND

CC

GND

LM3647 controls charge current

Slow

External (LM317) charge control

Fast

4.2V/Cell Li-Ion

Fast

4.1V/Cell Li-Ion

3.0 LM3647 REFERENCE

.

© 2001 National Semiconductor Corporation AN101315 www.national.com

AN-1164

The high speed PWM is filtered to a DC-level and fed into an
operational amplifier that controls a power-NPN transistor.
The LM3467 requires charge current feedback to control the
charge current.

1.2 Modes of Operation

AN101315-14

Charge Current

The charge settings for LM3647 current control are shown
below. If the external LM317 is used to control the charge
current then the jumpers J9, J10 and J13 have no relevance,
when using LM317 regulation mode, this jumper must be
placed in either position. If external (LM317) regulation is
used then set jumper J7 to position ″slow″; for LM3647
regulation set J7 to ″fast″.

LM3647 Current Regulation

The I jumper J10 is used to select between different current
sense resistors. The values available are 0.047Ω and

0.100Ω.

AN101315-12

The charge current is set with jumpers J9 and J13. The
figure shows two possible currents that depend on how
jumper J10 is set. The higher current is selected when J10 is
set to 0.047Ω and the lower current is selected when J10 is
set to 0.100Ω.

AN101315-13

1.0 FUNCTIONAL DESCRIPTION

1.1 General

The LM3647 has voltage and current sensing inputs that are
used to control a PWM-output. The voltage input is
connected to the battery via a resistor divider network, and
the current input is connected to an operational amplifier that
amplifies the voltage across a current sense resistor located
at the positive battery terminal. The PWM-output can be
configured as a high speed PWM, or as a low speed
(ON/OFF) output for an external current regulator. The latter
is for low cost Ni-Cd/Ni-MH charger applications, eliminating
the need for any operational amplifiers or current feedback
circuitry.

1.2.1 Charging Ni-Cd/Ni-MH Batteries

The charger detects that a battery is connected when the
CEL-pin
has been deeply discharged and does not have any voltage
across the battery terminals. This is accomplished by
applying a small ’pre-charge’ current once every minute for
up to 15 seconds. The deeply discharged battery will accept
this charge and the battery potential will eventually rise
above the 1.0V limit to initiate normal charging. When the
charger has detected a battery (CEL-pin
to see if the temperature is within range to start charging. If
it is, then it applies a small current of 0.2C for approximately
5 minutes. If the battery voltage exceeds the maximum
battery voltage (CEL-pin
charging and stays in error mode until the battery is
removed. If the battery voltage has not risen above the bad
battery threshold (CEL-pin
considered to be defective and the charger goes into error
mode. If the battery passes all tests, then after the five
minutes have passed, the charger starts the next phase:
Fast Charge.

During Fast Charge, the charger applies a constant current
to the battery and monitors both battery voltage and
temperature. The charger is looking for a drop in the battery
voltage that normally occurs at the end of the Fast Charge
cycle. The size of the voltage drop differs depending on
battery type (Ni-Cd/Ni-MH). For Ni-Cd it’s approximately 50
mV/cell and for Ni-MH it’s approximately 17 mV/cell. If the
temperature rise is larger than 50 mV/minute (∼1˚C/minute)
when charging Ni-MH batteries, the battery has reached the
end of the Fast Charge cycle.

During charging the temperature-input is constantly
measured to ensure that the battery’s temperature is within
proper range. If the temperature is out of range the charger
aborts the charge and goes into error mode.

During the next charge phase (Topping Charge) the LM3647
applies a small current of 0.2C for a time set by the
time-selection RC-network (see section below). This phase
may be followed by a Maintenance Charge phase,
depending on selection-pins.

1.2.2 Charging Li-Ion Batteries

The charger detects that a battery is connected when the
CEL-pin
has been deeply discharged and does not have any voltage
across the battery terminals. This is accomplished by
applying a small ’pre-charge’ current once every minute for
up to 15 seconds. The deeply discharged battery will accept
this charge and the battery potential will eventually rise
above the 1.0V limit to initiate normal charging. When the
charger has detected a battery (CEL-pin
to see if the temperature is within range to start charging. If
it is, then it applies a small current of 0.2C for approximately
1 minute. If the battery voltage is close to fully charged, the
charger will not reach the charging voltage within 1 minute,

>

1.0V. The charger can also detect a battery that

>

1.0V), it checks

>

3.017V), the LM3647 stops

<

1.2V), then the battery is

>

1.0V. The charger can also detect a battery that

>

1.0V), it checks

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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
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
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.

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).

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
restart threshold value (CEL
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
threshold value (CEL

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-

<

2.153V).

<

2.153V), or just maintenance

TABLE 1. Charge Timeouts

AN-1164

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.

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).

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.

1.2.2.2 Clarifications Regarding Circuit Schematics

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.

1.2.2.3 Setting The Charge Timeout

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.

Ni-Cd/Ni-MH

R Value C Value

100 kΩ 0 nF 75 20 50 75 3.2C
100 kΩ 10 nF 100 25 70 100 2.4C
100 kΩ 15 nF 160 40 110 160 1.4C
100 kΩ 22 nF 190 50 130 190 1.2C
100 kΩ 33 nF 260 65 170 260 0.9C
100 kΩ 47 nF 330 80 220 330 0.7C
100 kΩ 68 nF 450 115 300 450 0.5C
100 kΩ 100 nF 540 135 360 540 0.4C

EXAMPLE 1:

Fast Charge

(minutes)

Ni-Cd/Ni-MH

Topping (minutes)

Li-lon CC
(minutes)

Li-lon CV
(minutes)

AN101315-18

Appropriate

Charge Rates

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