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
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).
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.
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
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.
Vmin– 8 V
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
Rev. A3, 05-Mar-97