Rainbow-electronics MAX1641 Bedienungsanleitung PDF herunterladen (Seite 8)

MAX1640/MAX1641

The voltage at SET is given by:

R1 = R2 (V

REF

/ V

SET

-1 ); 10kΩ < R2 < 300kΩ

where V

REF

= 2V and V

SET

is proportional to the

desired output current level.

The MAX1640/MAX1641 are specified for V

SET

between 0V and V

REF

. For V

SET

> V

REF

, output current

increases linearly (with reduced accuracy) until it

clamps at V

SET

≈ 4V.

Pulse-Trickle Mode: Selecting the

Pulse-Trickle Current

Pulling D0 low and D1 high selects pulse-trickle mode.

This current equals V

SET

/ (13.3R

SENSE

) and remains

on for 12.5% of the period set by R

TOFF

. Pulse-trickle

current maintains full charge across the battery and

can slowly charge a cold battery before fast charging

commences.

Off Mode: Turning Off the Output Current

Pulling D0 and D1 low turns off the P-channel FET and

hence the output current flow. This mode also controls

end of charge and protects the battery against exces-

sive temperatures.

Setting the Maximum Output

Voltage Level

The maximum output voltage should be programmed to

a level higher than the output/battery voltage (I

LOAD

). An external resistor-divider between the output

and ground (Figure 4) sets the voltage at TERM. Once

the voltage at TERM exceeds the reference, the internal

comparator turns off the P-channel FET, terminating

current flow. Select R4 in the 10kΩ to 500kΩ range.

R3 is given by:

R3 = R4 (V

OUT

/ V

TERM

) -1

PERIOD = 3.2 x 10 x R (sec)

-7

TOFF

Adjustable-Output, Switch-Mode

Current Source with Synchronous Rectifier

8 _______________________________________________________________________________________

D1 DO MODE

OUTPUT CURRENT (A)

0 0 OFF 0

0 1 Top-Off V

SET

/ (13.3R

SENSE

)

1 0 Pulse-Trickle

SET

/ (13.3R

SENSE

)

12.5% duty cycle

1 1 Fast Charge V

REF

/ (13.3R

SENSE

)

Table 1. Selecting Output Current Levels

MAX1640

MAX1641

REF

SET

Figure 3. Adjusting the Output Current Level

MAX1640

CS+

TERM

CS-

SENSE

BATT

Figure 4a. Setting the Maximum Output Voltage Level

MAX1641

CS+

TERM

CS-

BATT

SENSE

Figure 4b. Setting the Maximum Output Voltage Level

1 2 3 4 5 6 7 8 9 10 11

MAX1640/MAX1641 1

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