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Simple Controller for Fast Charge Systems
U2407B
Description
The bipolar IC U2407B is a fast charge battery controller
for drained NiCd/ NiMH batteries. Apart from phase
control, it is identical with U2405B, but has four LED
outputs. The IC enables the designer to create an efficient
and economic charge system. The U2407B incorporates
an intelligent multiple-gradient battery-voltage moni-
toring combined with temperature and failure mode
detection. With automatic top-off charging, the
integrated circuit ensures that the charge device stops
regular charging before the critical stage of overcharging
is achieved. It incorporates an additional algorithm for
reactivating fully drained batteries especially after long
time storage. It has four LED driver outputs for different
indications of the charge status.
Features
D Multiple gradient monitoring
D Temperature window (Tmin/Tmax)
D Exact currentless measurement
D Four LED status outputs
D Linear power control
D Preferred for externally regulated current sources
D Preformation algorithm for drained batteries
D Programmable top-off charge function
Applications
D Primary switch mode
D AC/ DC wall plug adapter
D Ultra fast charger (10 minutes)
Package: DIP16/ SO16
13
VRef
6.5 V/10 mA
16 Switch output
Power - on control
14
Power supply
1 VS = 8 to 26 V
95 10648
4
12
Oscillator
Control unit
Gradient
d2V/dt2 and –dV
160 mV
Ref
Temp. control
Tmax Sensor
56
Figure 1. Block diagram
7
15 2 3 10
Status control
Scan path
Battery
detection
VRef = 5 V
VBatt monitor
0.1 to 4 V
Charge break
output
8
11
9
TELEFUNKEN Semiconductors
Rev. A4, 05-Mar-97
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U2407B
Input Voltage
8 V to 24 V
R7
WC10 1 k
m10 F
10 W
R1
Mounted
on
heatsink
D1
BYW52
BD649
T1 BC237
T2
WRB1
1k
WRB2
10 k
Ich
WRB3
10 k
WR4
2.2 k
WR5
2.2 k
LED1
LED2
LED3
LED4
R8
100 kW
OPO
1 mCFR
VBatt
C1 7mF
C1
VS
14
10
2
220 mF
GND
1
3
15
4
U2407B
13 VRef
9
Tmax
6
Battery
WRsh
0.2
R6
10 kW
7
Sensor
5
mC4 OPI
1F
8
tp
Output
16
12
11
STM
Osc
CO
10 nF
mC2
0.22 F
RT2
WRT3 100 k
W1.5 k
RO
270 kW
95 10677
Figure 2. Scheme for DC linear regulation
Pin Description
Package: DIP16/ SO16
GND 1
LED2 2
LED3 3
OPO 4
OPI 5
Tmax 6
Sensor 7
tp 8
16 Output
15 LED4
14 VS
13 VRef
12 Osc
11 STM
10 LED1
9 VBatt
95 10618
Pin Symbol
Function
1 GND Ground
2 LED2 Display output “top-off/ trickle
charge”
3 LED3 Display output “Fast charge”
4 OPO Operational amplifier output
5 OPI Operational amplifier input
6 Tmax Maximum temperature
7 Sensor Temperature sensor
8 tp Charge break output
9 VBatt Battery voltage
10 LED1 Display output “failure mode”
11 STM. Test mode switch (status control)
12 Osc Oscillator
13 VRef Reference output voltage
14 VS Supply voltage
15 LED4 Display output “top-off charge”
16 Output Trigger output
2 (16)
TELEFUNKEN Semiconductors
Rev. A3, 05-Mar-97

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U2407B
General Description
The integrated circuit, U2407B, is designed for charging
Nickel-Cadmium (NiCd) and Nickel-Metal-Hydride
(NiMH) batteries. Fast charging results in voltage lobes
when fully charged (figure 3). It supplies two
identifications ( i. e., + d2V/dt2, and – DV ) to end the
charge operation at the proper time.
As compared to the existing charge concepts where the
* *charge is terminated after voltage lobes according
to – DV and temperature gradient identification, the
U2407B takes into consideration the additional changes
in positive charge curves, according to the second
derivative of the voltage with respect to time (d2V/dt2).
The charge identification is the sure method of switching
off the fast charge before overcharging the battery. This
helps to give the battery a long life by hindering any
marked increase in cell pressure and temperature.
Even in critical charge applications, such as a reduced
charge current or with NiMH batteries where weaker
charge characteristics are present multiple gradient
control results in very efficient switch-off.
An additional temperature control input increases not
only the performances of the charge switching
characteristics but also prevents the general charging of
a battery whose temperature is outside the specified
window.
A specific preformation algorithm is implemented for
reactivating fully drained batteries especially in the case
of batteries that have been stored for a long time.
A constant charge current is necessary for continued
charge-voltage characteristic. This constant current is
generated from an external power supply and can be regu-
lated with the help of an internal op-amp regulator
(figure 2). An external current source can also be con-
trolled by the switch output Pin 16 (see figure 12).
For further information please refer to the applications.
Battery
voltage
5V
Battery insertion
preformation
ÎÎÎÎ1.6 V
DV
Fast charge stop
) d2V
dt2
Top-off charge stop
without
charge control
DV
) Dd2V
dt2
,
V
I (RB1)
95 10616
t1 = 5 min
Fast charge rate IO
Top-off
charge rate
1/4 IO
t2 = 20 min
Figure 3. Charge function diagram, fosc = 800 Hz
Trickle
charge rate
1/256 IO
t
TELEFUNKEN Semiconductors
Rev. A4, 05-Mar-97
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U2407B
Flow Chart Explanation, fosc = 800 Hz
(Figures 2, 3 and 4)
Battery pack insertion disables the voltage lock at battery
detection input Pin 9. All functions in the integrated
circuit are reset. For further description, DIP-pinning is
taken into consideration.
Battery Insertion and –DV
Monitoring
After battery insertion fast charge Io begins when the
input voltage VBatt is higher than 1.6 V. For the first
5 minutes the d2V/dt2-gradient recognition is suppressed,
DV monitoring is activated. In case the detected VBatt
voltage is less then 1.6 V the special preformation
procedure will be activated. The reference level with
respect to the cell voltage can be adjusted by the resistor
RB3 (see figure 2).
Preformation Procedure
Top-Off Charge Stage
By charge disconnection through the + d2V/dt2 mode, the
device switches automatically to a defined protective
top-off charge with a pulse rate of 1/4 IO (pulse time,
tp = 5.12 s, period, T = 20.48 s).
The top-off charge time is specified for a time of
20 minutes @ 800 Hz.
During top-off mode the LED4 is in ON mode.
Trickle Charge Stage
When top-off charge is terminated, the device switches
automatically to trickle charge with 1/256 IO (tp = 5.12 s,
period = 1310.72 s). The trickle continues until the
battery pack is removed.
During trickle mode the LED2 output is in on mode,
LED4 is in OFF-mode.
Before fast charge of fully drained or long-time stored
batteries begins, a reactivation of it is necessary. The
preformation current is dependent on pull-up resistor
RB1. The fast charge starts only after the VBatt is higher
than 1.6 V. During the first 10 minutes the green LED2 is
blinking. If after 10 minutes, VBatt voltage has not
reached the reference level, the indication changes to red
blinking LED1. The charge will continue with
preformation rate I (RB1). In case VBatt increases to 1.6 V
reference level, the fast charge rate current, Io, is
switched-on and the green LED2 is blinking.
DV Cut-Off (Monitoring)
When the signal at Pin 9 of the DA converter is 12 mV
below the actual value, the comparator identifies it as a
voltage drop of –DV. The validity of –DV cut-off is
considered only if the actual value is below 12 mV for
three consecutive cycles of measurement.
d2V/dt2-Gradient
If there is no charge stop within the first 5 minutes after
battery insertion, then d2V/dt2 monitoring will be active.
In this actual charge stage, all stop-charge criteria are
active.
Basic Description
Power Supply, Figure 2
The charge controller allows the direct power supply of
8 to 26 V at Pin 14. Internal regulation limits higher input
voltages. Series resistance, R1, regulates the supply cur-
rent, IS, to a maximum value of 25 mA. Series resistance
is recommended to suppress the noise signal, even below
26 V limitation. It is calculated as follows.
wR1min
Vmax–26 V
25 mA
vR1max
Vmin– 8 V
Itot
where
Itot = IS + IRB1 + I1
Vmax, Vmin = Rectified voltage
IS = Current consumption (IC) without load
IRB1 = Current through resistance, RB1
I1 = Trigger current at Pin 1
When close to the battery’s capacity limit, the battery
voltage curve will typically rise. As soon as the +d2V/dt2
stop-charging criteria are met, the device will stop the fast
charge activities.
4 (16)
TELEFUNKEN Semiconductors
Rev. A3, 05-Mar-97

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Start Power on reset
LED1,2,3,4 off
U2407B
*) 70 mV > VBatt > 5V
yes
Batt. inserted
*)
Reset
no
no
LED1 blinking
Temp. range
ok ?
Preformation
yes current I RB1
LED3 blinking
Temp. range
ok ?
yes
Charge stop
no
LED1 blinking
Fast charge
begins
yes
VBatt > 1.6 V
no
yes
tch > 10 min
VBatt 4 V
yes
–dV
no switch off
no
Batt. inserted
*)
yes
no
Charge time
t1 > 5 min ?
no
LED1 blinking
LED3 off
–dV and d2V/dt2
yes monitoring activated
yes
Batt. inserted
no
*)
Batt temp
no range?
yes
LED1 blinking
–dV
disconnect
no
d2V/dt2
disconnect ?
no
LED2 on
LED2 on
LED4 on
Trickle charge
1/256 IO
Top off charge
1/4 IO
yes
Batt. inserted
*)
no
yes no
t2 > 20 min
Figure 4. Flow chart
95 10671
TELEFUNKEN Semiconductors
Rev. A4, 05-Mar-97
5 (16)