U2405B Datasheet, PDF (5/17 Pages) TEMIC Semiconductors – Fast Charge Controller for Drained NiCd/NiMH Batteries

U2405B
Flow Chart Explanation, f_osc = 800 Hz
(Figures 2, 3 and 4)
Battery pack insertion disables the voltage lock at battery
detection input Pin 10. 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 I_o begins when the
input voltage V_Batt 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 V_Batt
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
R_B3 (see figure 2).
Preformation Procedure
Before fast charge of fully drained or long time stored
batteries begin, a reactivation is necessary. The
preformation current is dependent on pull-up resistor
R_B1. The fast charge starts only after the V_Batt is higher
than 1.6 V level. During the first 10 minutes the green
LED2 is blinking. If, after 10 minutes, V_Batt voltage has
not reached the reference level, the indication changes to
red blinking LED1. The charge will continue with
preformation rate I (R_B1). In case V_Batt increases to 1.6 V
reference level, the fast charge rate current, I_o, is
switched-on and the green LED2 is blinking.
–DV Cut-Off (Monitoring)
When the signal at Pin 10 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.
When close to the battery’s capacity limit, the battery
voltage curve will typically rise. As long as the +d²V/dt²
stop-charging criteria are met, the device will stop the fast
charge activities.
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 I_O (pulse time,
t_p = 5.12 s, period, T = 20.48 s).
The top-off charge time is specified for a time of
20 minutes @ 800 Hz.
Trickle Charge Stage
When top-off charge is terminated, the device switches
automatically to trickle charge with 1/256 I_O (t_p = 5.12 s,
period = 1310.72 s). The trickle continues until the
battery pack is removed.
Basic Description
Power Supply, Figure 2
The charge controller allows the direct power supply of
8 to 26 V at Pin 15. Internal regulation limits higher input
voltages. Series resistance, R₁, regulates the supply
current, I_S, 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.
w R_1min
V_max–26 V
25 mA
v R_1max
V_min– 8 V
I_tot
where
I_tot = I_S + I_RB1 + I₁
V_max, V_min = Rectified voltage
I_S = Current consumption (IC) without load
I_RB1 = Current through resistance, R_B1
I₁ = Trigger current at Pin 1
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96
5 (17)