LTC4101EG Просмотр технического описания (PDF) - Linear Technology

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LTC4101EG

Smart Battery Charger Controller

Linear Technology 

LTC4101

OPERATION

DCIN and CLP is ever less than –25mV, then the input FET

is turned off quickly to prevent significant reverse current

from flowing in the input FET. In this condition the CHGEN

pin is driven low and the charger is disabled.

The AC Present Block (AC_PRESENT)

The DCDIV pin is used to determine AC presence. If the

DCDIV voltage is above the DCDIV comparator threshold

(VACP), then the ACP output pin will be switched to VDD

and the AC_PRESENT bit in the ChargerStatus() func-

tion will be set. If the DCDIV voltage is below the DCDIV

comparator threshold minus the DCDIV comparator

hysteresis, then the ACP output pin is switched to GND

and the AC_PRESENT bit in the ChargerStatus() function

is cleared. The ACP output pin is designed to drive 2mA

continuously.

Adapter Limiting

An important feature of the LTC4101 is the ability to auto-

matically adjust charging current to a level which avoids

overloading the wall adapter. This allows the product to

operate at the same time that batteries are being charged

without complex load management algorithms. Addition-

ally, batteries will automatically be charged at the maximum

possible rate of which the adapter is capable.

This feature is created by sensing total adapter output cur-

rent and adjusting charging current downward if a preset

adapter current limit is exceeded. True analog control is

used, with closed loop feedback ensuring that adapter load

current remains within limits. Amplifier CL1 in Figure 9

senses the voltage across RCL, connected between the

CLP and CLN pins. When this voltage exceeds 100mV, the

amplifier will override programmed charging current to limit

adapter current to 100mV/RCL. A lowpass filter formed by

4.99k and 0.1μF is required to eliminate switching noise.

If the current limit is not used, CLP should be connected

to CLP, but leave CLN connected to power.

Setting Input Current Limit

To set the input current limit, you need to know the mini-

mum wall adapter current rating. Subtract 7% for the input

current limit tolerance and use that current to determine

the resistor value.

RCL = 100mV/ILIM

ILIM = Adapter Min Current –

(Adapter Min Current • 7%)

As is often the case, the wall adapter will usually have at

least a +10% current limit margin and many times one

can simply set the adapter current limit value to the actual

adapter rating (see Figure 9).

ILIMIT/8

0

~40ms

AVERAGE CHARGER CURRENT

4101 F08

Figure 8. Charging Current Waveform in Low Current Mode

LTC4101

CLP

24

VIN

CL1

CLN

C9

0.1μF

RCL*

23

100mV

R1

4.99k

INFET

4

TO LOAD

*RCL

=

100mV

ADAPTER CURRENT

LIMIT

4101 F09

Figure 9. Adapter Current Limiting

4101fa

21

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