LTC3566 datasheet(13/28 Pages) LINER

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LTC3566

3566fa

on CLPROG represents the average input current of the

switching regulator. When the input current approaches

the programmed limit, CLPROG reaches VCLPROG, 1.188V

and power out is held constant.

The input current is programmed by the ILIM0 and ILIM1

pins. It can be conﬁgured to limit average input current to

one of several possible settings as well as be deactivated

(USB Suspend). The input current limit will be set by the

VCLPROG servo voltage and the resistor on CLPROG ac-

cording to the following expression:

VBUS = IBUSQ +

CLPROG

•(h

CLPROG + 1)

Figure 1 shows the range of possible voltages at VOUT as

a function of battery voltage.

consists of a precision ampliﬁer that enables a large on-

chip P-channel MOSFET transistor whenever the voltage at

VOUT is approximately 15mV (VFWD) below the voltage at

BAT. The resistance of the internal ideal diode is approxi-

mately 180mΩ. If this is sufﬁcient for the application, then

no external components are necessary. However, if more

conductance is needed, an external P-channel MOSFET

transistor can be added from BAT to VOUT.

When an external P-channel MOSFET transistor is present,

the GATE pin of the LTC3566 drives its gate for automatic

ideal diode control. The source of the external P-chan-

nel MOSFET should be connected to VOUT and the drain

should be connected to BAT. Capable of driving a 1nF load,

the GATE pin can control an external P-channel MOSFET

transistor having an on-resistance of 40mΩ or lower.

Suspend LDO

If the LTC3566 is conﬁgured for USB suspend mode, the

switching regulator is disabled and the suspend LDO

provides power to the VOUT pin (presuming there is power

available to VBUS). This LDO will prevent the battery from

running down when the portable product has access to

a suspended USB port. Regulating at 4.6V, this LDO only

becomes active when the switching converter is disabled

(suspended). To remain compliant with the USB speciﬁca-

tion, the input to the LDO is current limited so that it will

not exceed the 500μA low power suspend speciﬁcation.

If the load on VOUT exceeds the suspend current limit,

the additional current will come from the battery via the

ideal diode.

OPERATION

BAT (V)

2.4

4.5

4.2

3.9

3.6

3.3

3.0

2.7

2.4

3.3

3.9

3566 F01

2.7

3.0

3.6

4.2

NO LOAD

300mV

Figure 1. VOUT vs BAT

Figure 2. Ideal Diode Operation

FORWARD VOLTAGE (mV) (BAT – VOUT)

600

1800

2000

2200

120

240 300

3566 F02

200

1400

1000

400

1600

1200

800

180

360

480

420

VISHAY Si2333

OPTIONAL EXTERNAL

IDEAL DIODE

LTC3566

IDEAL DIODE

SEMICONDUCTOR

MBRM120LT3

Ideal Diode from BAT to VOUT

The LTC3566 has an internal ideal diode as well as a con-

troller for an optional external ideal diode. The ideal diode

controller is always on and will respond quickly whenever

VOUT drops below BAT.

If the load current increases beyond the power allowed

from the switching regulator, additional power will be

pulled from the battery via the ideal diode. Furthermore,

if power to VBUS (USB or wall power) is removed, then all

of the application power will be provided by the battery via

the ideal diode. The transition from input power to battery

power at VOUT will be quick enough to allow only a 10μF

capacitor to keep VOUT from drooping. The ideal diode

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