U2405B
Battery Voltage Measurement
The battery voltage measurement at Pin 10 (ADC-
converter) has a range of 0 V to 4 V, which means a
battery pack containing two cells can be connected
without a voltage divider.
4 V) a safety
If the AD converter is overloaded (V
Batt
switch off occurs. The fast charge cycle is terminated by
automatically changing to the trickle charge.
Precaution should be taken that under specified charge
current conditions, the final voltage at the input of the
converter, Pin 10, should not exceed the threshold voltage
level of the reset comparator, which is 5 V. When the
battery is removed, the input (Pin 10) is terminated across
the pulled-up resistance, R
B1,
to the value of 5 V-reset-
threshold. In this way, the start of a new charge sequence
is guaranteed when a battery is reinserted.
If the battery voltage exceeds the converter range of 4 V,
adjusting it by the external voltage divider resistance, R
B2
and R
B3
is recommended.
Value of the resistance, R
B3
is calculated by assuming
R
B1
= 1 k
W
, R
B2
= 10 k
W
, as follows:
R
B3
w
+
R
B2
V
10max
V
Bmax
– V
10max
The minimum supply voltage, V
smin
, is calculated for
reset function after removing the inserted battery
according to:
V
smin
+
0.03mA
@
R
B3
R
B1
)
R
)
5V
B2
R
B1
R
B3
)
R
)
R
B2
B3
where:
V
10max
= Max voltage at Pin 10
V
Smin
= Min supply voltage at the IC (Pin 15)
V
Bmax
= Max battery voltage
The voltage conditions mentioned above are measured
during charge current break (switch-off condition).
15
R
B1
V
S
V
DAC
–
+
V
Ref
=
12 mV
=
V
DAC
–
+
Reset
comparator
V
Ref
=
4.3 V
Reset
–
+
DAC control
comparator
- dV Recognition
I
ch
V
B
V
6
R
sh
R
B3
Battery
R
B2
V
Batt
10
7V
95 10174
V
Ref
= 0.1 V
Figure 5. Input configuration for the battery voltage measurement
Table 1. valid when V
10max
= 3.5 V
Cell No.
V
Smin
(V)
R
B3
(k
W)
1
8
–
2
8
–
3
8
51
4
9
16
5
11
10
6
13
7.5
7
15
5.6
8
17
4.7
9
19
3.9
10
21
3.3
11
23
3
12
25
2.7
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96
7 (17)
TEMIC [ TEMIC SEMICONDUCTORS ]
