MC33342 Просмотр технического описания (PDF) - ON Semiconductor

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MC33342

Battery Fast Charge Controllers

ON Semiconductor 

MC33340, MC33342

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:

DR(TLow

³

THigh)

+

VH(T)

Iin

+

44

30

mV

mA

+ 1.46 k

The resistance change approximates a thermal hysteresis

of 2°C with a 10 kW 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 4 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 Overtemperature

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 −DV

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 −DV 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 Table 2.

Table 1. 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

Open

Open

Open

Time

Open

Open

GND

Time

Open

GND

Open

Time

Open

GND

GND

Time

GND

Open

Open

Time

GND

Open

GND

Time

GND

GND

Open

Temperature

0 V to VCC − 0.7 V

0 V to VCC − 0.7 V

0 V to VCC − 0.7 V

Time Limit

Fast Charge

(Minutes)

283

247

212

177

141

106

71

Timer Disabled

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