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Charge Timer
U2403B
Description
The U2403B is a monolithic, integrated-bipolar circuit
which can be used in applications for time-controlled,
constant-current charge. Selection of charge current
versus timing is carried out by using the external circuit
at Pins 2, 3 and 4. For high current requirement, an
external transistor is recommended in series with the
battery. To protect the IC against high power loss
(typically > 140°C), the oscillator is shut down when the
reference voltage is switched off (0 V). The latter also
takes place when there is a saturation caused by collector
voltage at Pin 1. When the overtemperature has
disappeared and the collector voltage at Pin 1 has
exceeded the supply voltage (V1 > VS), charge time
operation continues (see flow chart in figure 3).
Features
D Easy-to-run autonomous dual rate charger
D Constant charge current
D 3 h – 24 h charge time programmable
D Low cost dc regulator
D Overtemperature protection
D Charge-mode indication
D Operation starts at the moment of battery insertion
D Fast charge time-test mode
Applications
D Cordless telephones
D Low-cost battery-charge timer
D Entertainment
Package: DIP8, SO8
Block Diagram
Power
supply
AC/DC
Battery
inserted
LED2
Charge
R1
R5
LED
LED1
Ready
8
C1
VS GND
67
94 8629
Charge mode
indicator
Power supply
VS = 3.5 to 12 V
Test
mode
5 STM
í max
140°C
1
V1
í
2
Shunt
Timer and control logic
VRef = 1.5 V/ 0.1 V/ 0 V
VRef
+
RC
oscillator
3
Sense
4
Osc
R3 R4
C4
Figure 1. Block diagram with external circuit
TELEFUNKEN Semiconductors
Rev. A2, 14–Nov–96
1 (12)

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U2403B
Pin Description
V1 1
V2 2
Sense 3
Osc 4
8 LED
7 GND
6 VS
5 STM
Pin Symbol
Function
1 V1 Collector terminal
2 V2 Shunt emitter terminal
3 V3 Amplifier sense input
4 Osc Oscillator input
5 STM Test mode switch
6 VS Supply voltage
7 GND Reference point, GND
8 LED Charge mode indicator
94 8685
Pin 1, Collector Voltage V1
Pin 1 is an open collector output. When V1 3 V, the
charge cycle is switched off until it is above the supply
voltage, as shown in figure 6.
Pin 2, Shunt Emitter
123
Pin 4 Oscillator
256
Pulse
The constant current source is supplied by the internal
operational amplifier. The voltage across R3 is deter-
mined via the internal reference source.
Ich = V3/R3 (V3 = Vsense)
Pin 3, Amplifier Sense Input (Inverted)
Pin 5 Test – Mode
94 8839
Figure 2. Quick test timer 1/3
The voltage-regulated current source has a closed loop at
Pin 2, Pin 3, and resistor R3.
Pin 4, Oscillator Input R4, C4
Selection of current charge versus timing is carried out by
using the external circuit at Pins 2, 3, and 4. Typical
values are given in charge characteristics (see table next
page).
Pin 5, Test-Mode Switch for Charging Time
The charging time, tch, is given by the following equation.
+tch
1
fosc
2n
where:
fosc = oscillator frequency (see figure 2)
n = frequency divider
= 26, if STM open
= 17, if STM = GND
= 8, if STM = VS
The first eight divider stages can be tested directly.
256 input tact signals at Pin 4 create one tact signal at
Pin 5.
Example
Assume a charge time of 6 h.
Select the values of R4 and C4 from the tables next page.
For example:
WR4 = 470 k
C4 = 680 pF
There is a frequency of approximately 3100 Hz at Pin 4.
It is possible to test the charge time of 6 h by running
through the charge cycle for a very short time. By
connecting Pin 5 with GND, the test time is 42 s. By
connecting Pin 5 with Pin 1 (V1), the test time is reduced
to about 82.4 ms. R5 is connected in parallel to the LED2
and provides a protective bypass function for the LED
(see figure 1).
Pin 6, Supply Voltage, VS
[VS 3.1 V power-on reset release (turn-on)
[VS 2.9 V under-voltage reset
[VS 13 V supply voltage limitation
Pin 7, Ground
2 (12)
TELEFUNKEN Semiconductors
Rev. A1, 20-Mar-96

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U2403B
Pin 8, Charge Mode Indicator
An open-collector output supplies constant current to
LED1 after the active charge phase has been terminated.
ímax controls the function temperature for the final stage
range. This is when the temperature is above 140°C and
the charge function is therefore switched off.
Trickle Charge
The trickle charge starts after the charge has been termi-
nated. In this case, the internal reference voltage is
reduced from 1.5 V to approximately 0.1 V. This means
the charge current is decreased by the factor:
K = 1.5 V/ 0.1 V = 15.
Trickle current = Ich / 15 + I6 (supply current) + I8
It is possible to reduce the trickle charge with resistor R6,
as shown in figures 6 and 7.
Charge Characteristics
Charge Time
Test time/ Test-Mode Switch STM
Open VS GND
3h
41.2 ms
21 s
4h
54.9 ms
28 s
5h
68.6 ms
35 s
6h
82.4 ms
42 s
7h
96.1 ms
49 s
8h
109.8 ms
56 s
9h
123.6 ms
1 min 3 s
10 h
137.3 ms
1 min 10 s
12 h
164.8 ms
1 min 24 s
16 h
219.7 ms
1 min 56 s
Oscillator Components
R4 (KW)
C4 (pF)
510 270
430 330
300 470
620 330
430 470
300 680
510 470
390 680
300 1000
620 470
470 680
360 1000
560 680
430 1000
220 2200
620 680
470 1000
200 2200
750 680
510 1000
240 2200
620 820
270 2200
130 4700
390 2200
150 4700
470 2200
200 4700
Frequency
fosc (Hz)
6213
4660
3728
3105
2663
2330
2071
1864
1553
1165
TELEFUNKEN Semiconductors
Rev. A2, 14–Nov–96
3 (12)