MC33340EVK View Datasheet(PDF) - ON Semiconductor
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MC33340EVK Datasheet PDF : 12 Pages
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MC33340 MC33342
Fast Charge Timer
A programmable backup charge timer is available for fast
charge termination. The timer is activated by the Time/Temp
Select comparator, and is programmed from the t1/Tref High,
t2/Tsen, and t3/Tref Low inputs. If one or more of these inputs
is allowed to go above VCC – 0.7 V or is left open, the
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 Figure 10.
Over/Under Temperature Detection
A backup over/under temperature detector is available
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 VCC – 0.7 V.
Temperature sensing is accomplished by placing a
negative temperature coefficient (NTC) thermistor in thermal
contact with the battery pack. The thermistor connects to the
t2/Tsen input which has a 30 µA current source pull–up for
developing a temperature dependent voltage. The
temperature limits are set by a resistor that connects from the
t1/Tref High and the t3/Tref Low inputs to ground. Since all
three inputs contain matched 30 µA 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/Tsen input.
The lower comparator senses the presence of an under
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
switching between the fast and trickle modes as the lower
temperature limit is crossed. The amount of temperature rise
to overcome the hysteresis is determined by the thermistor’s
rate of resistance change or sensitivity at the under
temperature trip point. The required resistance change is:
³ + + + DR(TLow
THigh)
VH(T)
Iin
44 mV
30 mA
1.46 k
The resistance change approximates a thermal hysteresis
of 2°C with a 10 kΩ thermistor operating at 0°C. The under
temperature fast charge inhibit feature can be disabled by
biasing the t3/Tref Low input to a voltage that is greater than
that present at t2/Tsen, and less than VCC – 0.7 V. Under
extremely cold conditions, it is possible that the thermistor
resistance can become too high, allowing the t2/Tsen input to
go above VCC – 0.7 V, and activate the timer. This condition
can be prevented by placing a resistor in parallel with the
thermistor. Note that the time/temperature threshold of VCC
– 0.7 V is a typical value at room temperature. Refer to the
Electrical Characteristics table and to Figure 3 for additional
information.
The upper comparator senses the presence of an over
temperature condition. When the upper temperature limit is
exceeded, the comparator output sets the Over Temperature
Latch and the charger is switched to trickle mode. Once the
latch is set, the charger cannot be returned to fast charge,
even after the temperature falls below the limit. This feature
prevents the battery pack from being continuously
temperature cycled and overcharged. The latch can be reset
by removing and reconnecting the battery pack or by cycling
the power supply voltage.
If the charger does not require either the time or
temperature backup features, they can both be easily
disabled. This is accomplished by biasing the t3/Tref Low
input to a voltage greater than t2/Tsen, and by grounding the
t1/Tref High input. Under these conditions, the Time/Temp
Select comparator output is low, indicating that the
temperature mode is selected, and that the t2/Tsen input is
biased within the limits of an artificial temperature window.
Charging of battery packs that are used in portable power
tool applications typically use temperature as the only means
for fast charge termination. The MC33340/342 can be
configured in this manner by constantly resetting the –∆V
detection logic. This is accomplished by biasing the Vsen
input
to
≈1.5 V from a two resistor divider that is connected between
the positive battery pack terminal and ground. The Vsen Gate
output is also connected to the Vsen input. Now, each time
that the Sample Timer causes the Vsen output to go low, the
Vsen input will be pulled below the undervoltage threshold of
1.0 V. This causes a reset of the –∆V logic every 1.38
seconds, thus disabling detection.
Operating Logic
The order of events in the charging process is controlled
by the logic circuitry. Each event is dependent upon the input
conditions and the chosen method of charge termination. A
table summary containing all of the possible operating modes
is shown in Figure 11.
Figure 10. Fast Charge Backup Termination Time/Temperature Limit
Backup
Termination
Mode
t3/Tref Low
(Pin 5)
Programming Inputs
t2/Tsen
(Pin 6)
t1/Tref High
(Pin 7)
Time Limit
Fast Charge
(Minutes)
Time
Open
Open
Open
283
Time
Open
Open
Gnd
247
Time
Open
Gnd
Open
212
Time
Open
Gnd
Gnd
177
Time
Gnd
Open
Open
141
Time
Gnd
Open
Gnd
106
Time
Gnd
Gnd
Open
71
Temperature
0 V to VCC – 0.7 V 0 V to VCC – 0.7 V 0 V to VCC – 0.7 V Timer Disabled
MOTOROLA ANALOG IC DEVICE DATA
7
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