MC33342 Просмотр технического описания (PDF) - ON Semiconductor

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MC33342

Battery Fast Charge Controllers

ON Semiconductor 

MC33340, MC33342

Negative slope voltage detection starts after 60 ms have

elapsed in the fast charge mode. This does not affect the

Fast/Trickle output until the holdoff time (thold) has elapsed

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

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 Vsen

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.

Synchronous

FV = Vsen (24 kHz)

Vsen

Voltage to

Input

Frequency

Ck

Rachet

Converter

Counter

Battery Detect

Low High UVLO

F/T

−DV

Logic

SCK

95 kHz

Sample

Timer

Trickle Mode

Holdoff

Over Under Charge

Temperature Timer

Vsen Gate

Vsen Gate

Preset

Convert

11 ms

1.38 s

22 ms

Rachet Counter Convert

0 to 1023 FV Pulses

Figure 10. Negative Slope Voltage Detector

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 Table 1.

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 mA 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 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/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

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