MC33342 ON Semiconductor, MC33342 Datasheet - Page 6

• Manufacturer Part Number: MC33342
• Description: (MC33340 / MC33342) Battery Fast Charge Controllers
• Manufacturer: ON Semiconductor

power is applied to V
occur as a result of three possible conditions. The first is if
the V
2.0 V indicates that the battery pack is open or disconnected,
while below 1.0 V indicates the possibility of a shorted or
defective cell. The second condition is when the
MC33340/342 detects a fully charged battery by measuring
a negative slope in battery voltage. The MC33340/342
recognize a negative voltage slope after the preset holdoff
time (t
indicates that the battery pack is fully charged. The third
condition is either due to the battery pack being out of a
programmed temperature range, or that the preset timer
period has been exceeded.
return from trickle to fast charge mode. The first is if the V
input voltage moved to within the 1.0 to 2.0 V range from
initially being either too high or too low. The second is if the
battery pack temperature moved to within the programmed
temperature range, but only from initially being too cold.
Third is by cycling V
internal logic to reset. A concise description of the major
circuit blocks is given below.
Negative Slope Voltage Detection
voltage detector is shown in Figure 10. It includes a
Synchronous Voltage to Frequency Converter, a Sample
Timer, and a Ratchet Counter. The V
the Voltage to Frequency Converter (VFC), and it connects
to the rechargeable battery pack terminals through a
The MC33340/342 starts up in the fast charge mode when
There are three conditions that will cause the controller to
A representative block diagram of the negative slope
sen
hold
input voltage is above 2.0 V or below 1.0 V. Above
) has elapsed during a fast charge cycle. This
CC
CC
. A change to the trickle mode can
Figure 9. Typical Charge Characteristics for NiCd and NiMh Batteries
1.6
1.5
1.4
1.3
1.2
1.1
1.0
off and then back on causing the
0
sen
pin is the input for
Voltage
Relative Pressure
Temperature
40
OPERATING DESCRIPTION
CHARGE INPUT PERCENT OF CAPACITY
MC33340, MC33342
http://onsemi.com
sen
80
6
resistive voltage divider. The input has an impedance of
approximately 6.0 MW and a maximum voltage range of
−1.0 V to V
The 10 V upper limit is set by an internal zener clamp that
provides protection in the event of an electrostatic discharge.
The VFC is a charge−balanced synchronous type which
generates output pulses at a rate of F
signal (SCK) to the VFC. This signal synchronizes the F
output to the other Sample Timer outputs used within the
detector. At 1.38 second intervals the V
low for a 33 ms period. This output is used to momentarily
interrupt the external charging power source so that a precise
voltage measurement can be taken. As the V
low, the internal Preset control line is driven high for 11 ms.
During this time, the battery voltage at the V
allowed to stabilize and the previous F
At the Preset high−to−low transition, the Convert line goes
high for 22 ms. This gates the F
counter for a comparison to the preloaded count. Since the
Convert time is derived from the same clock that controls the
VFC, the number of F
frequency. If the new sample has more counts than were
preloaded, it becomes the new peak count and the cycle is
repeated 1.38 seconds later. If the new sample has two fewer
counts, a less than peak voltage event has occurred, and a
register is initialized. If two successive less than peak
voltage events occur, the −DV ‘AND’ gate output goes high
and the Fast/Trickle output is latched in a low state,
signifying that the battery pack has reached full charge
status.
The Sample Timer circuit provides a 95 kHz system clock
V
max
CC
T
120
max
+ 0.6 V or 0 V to 10 V, whichever is lower.
dV
V
dt
pulses is independent of the clock
−DV
160
70
60
50
40
30
20
10
V
pulses into the ratchet
V
V
= V
sen
count is preloaded.
Gate output goes
sen
sen
(24 kHz).
sen
Gate goes
input is
V