MC33342 ON Semiconductor, MC33342 Datasheet - Page 7

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

elapsed in the fast charge mode. This does not affect the
Fast/Trickle output until the holdoff time (t
during the fast charge mode. Two scenarios then exist.
Trickle mode holdoff is implemented to ignore any initial
drop in voltage that may occur when charging batteries that
have been stored for an extended time period. If the negative
slope voltage detector senses that initial drop during the
holdoff time, and the input voltage rises as the battery
charges, the Fast/Trickle output will remain open. However,
if the negative slope voltage detector senses a negative drop
Fast Charge Timer
charge termination. The timer is activated by the Time/Temp
Select comparator, and is programmed from the t1/T
High, t2/T
inputs is allowed to go above V
comparator output will switch high, indicating that the timer
feature is desired. The three inputs allow one of seven
possible fast charge time limits to be selected. The
programmable time limits, rounded to the nearest whole
minute, are shown in Table 1.
Over/Under Temperature Detection
and can be used in place of the timer for fast charge
termination. The timer is disabled by the Time/Temp Select
comparator when each of the three programming inputs are
held below V
Negative slope voltage detection starts after 60 ms have
A programmable backup charge timer is available for fast
A backup over/under temperature detector is available
Input
V
sen
sen
, and t3/T
CC
− 0.7 V.
V
Synchronous
sen
Convert
Frequency
Voltage to
ref
Converter
Preset
Gate
Low inputs. If one or more of these
95 kHz
SCK
CC
11 ms
− 0.7 V or is left open, the
F
V
Figure 10. Negative Slope Voltage Detector
= V
Rachet Counter Convert
sen
hold
0 to 1023 F
(24 kHz)
) has elapsed
22 ms
MC33340, MC33342
Sample
V
Timer
http://onsemi.com
Pulses
Ck
ref
7
Counter
Rachet
1.38 s
in voltage during the holdoff time and the input voltage
never rises above that last detected level, the Fast/Trickle
output will latch into a low state. The negative slope voltage
detector has a maximum resolution of 2.0 V divided by
1023 mV, or 1.955 mV per count with an uncertainty of
±1.0 count. This yields a detection range of 1.955 mV to
5.865 mV. In order to obtain maximum sensing accuracy,
the R2/R1 voltage divider must be adjusted so that the V
input voltage is slightly less than 2.0 V when the battery pack
is fully charged. Voltage variations due to temperature and
cell manufacturing must be considered.
negative temperature coefficient (NTC) thermistor in
thermal contact with the battery pack. The thermistor
connects to the t2/T
source pull−up for developing a temperature dependent
voltage. The temperature limits are set by a resistor that
connects from the t1/T
ground. Since all three inputs contain matched 30 mA
current source pull−ups, the required programming resistor
values are identical to that of the thermistor at the desired
over and under trip temperature. The temperature window
detector is composed of two comparators with a common
input that connects to the t2/T
temperature condition. When the lower temperature limit is
exceeded, the charger is switched to the trickle mode. The
comparator has 44 mV of hysteresis to prevent erratic
Trickle Mode
Temperature sensing is accomplished by placing a
The lower comparator senses the presence of an under
Holdoff
V
sen
−DV
Gate
sen
Battery Detect
Over
Low
Temperature
ref
input which has a 30 mA current
High and the t3/T
Logic
Under
High
sen
Charge
UVLO
Timer
input.
ref
Low inputs to
F/T
sen