LTC3567 datasheet(13/28 Pages) LINER

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LTC3567

3567f

OPERATION

Figure 1. VOUT vs BAT

set to exceed the allowable USB current, the USB speciﬁca-

tion will not be violated. The switching regulator will limit

the average input current so that the USB speciﬁcation

is never violated. Furthermore, load current at VOUT will

always be prioritized and only remaining available power

will be used to charge the battery.

If the voltage at BAT is below 3.3V, or the battery is not

present and the load requirement does not cause the switch-

ing regulator to exceed the USB speciﬁcation, VOUT will

regulate at 3.6V, thereby providing “Instant-On” operation.

If the load exceeds the available power, VOUT will drop to

a voltage between 3.6V and the battery voltage. If there

is no battery present when the load exceeds the available

USB power, VOUT can drop toward ground.

The power delivered from VBUS to VOUT is controlled

by a 2.25MHz constant-frequency step-down switching

regulator. To meet the USB maximum load speciﬁcation,

the switching regulator includes a control loop which

ensures that the average input current is below the level

programmed at CLPROG.

The current at CLPROG is a fraction (hCLPROG–1)oftheVBUS

current. When a programming resistor and an averaging

capacitor are connected from CLPROG to GND, the voltage

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 pro-

grammed by the B1 and B0 bits of the I2C serial port. 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 according to

the following expression:

IVBUS =IBUSQ +

VCLPROG

RCLPROG

•(hCLPROG +1)

Figure 1 shows the range of possible voltages at VOUT as

a function of battery voltage.

Ideal Diode from BAT to VOUT

The LTC3567 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 internal 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 the 10μF

capacitor to keep VOUT from drooping. The ideal diode

consists of a precision ampliﬁer that enables a large on-

Figure 2. 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

3567 F01

2.7

3.0

3.6

4.2

NO LOAD

300mV

FORWARD VOLTAGE (mV) (BAT – VOUT)

600

1800

2000

2200

120

240 300

3567 F02

200

1400

1000

400

1600

1200

800

180

360

480

420

VISHAY Si2333

OPTIONAL EXTERNAL

IDEAL DIODE

LTC3567

IDEAL DIODE

SEMICONDUCTOR

MBRM120LT3

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