LTC4160 datasheet(14/32 Pages) LINER

14 / 32 page

LTC4160/LTC4160-1

41601f

OPERATION

the programmed limit, CLPROG reaches 1.18V and power

delivered by the switching regulator is held constant.

The input current limit is programmed by the ILIM0 and

ILIM1 pins. The input current limit has four possible set-

tings ranging from the USB suspend limit of 500μA up

to 1A for wall adapter applications. Two of these settings

are speciﬁcally intended for use in the 100mA and 500mA

USB application. Refer to Table 1 for current limit settings

using ILIM0 and ILIM1.

Table 1. USB Current Limit Settings Using ILIM0 and ILIM1

ILIM1

ILIM0

USB SETTING

1x Mode (USB 100mA Limit)

10x Mode (Wall 1A Limit)

Low Power Suspend (USB 500μA Limit)

5x Mode (USB 500mA Limit)

When the switching regulator is activated, the average

input current will be limited by the CLPROG programming

resistor according to the following expression:

VBUS

VBUSQ

CLPROG

()

•1

where IVBUSQ is the quiescent current of the LTC4160/

LTC4160-1, VCLPROG is the CLPROG servo voltage in

current limit, RCLPROG is the value of the programming

resistor and hCLPROG is the ratio of the measured cur-

rent at VBUS to the sample current delivered to CLPROG.

Refer to the Electrical Characteristics table for values of

hCLPROG, VCLPROG and IVBUSQ. Given worst-case circuit

tolerances, the USB speciﬁcation for the average input

current in 100mA or 500mA mode will not be violated,

provided that RCLPROG is 3.01k or greater.

While not in current limit, the switching regulator’s

Bat-Track feature will set VOUT to approximately 300mV

above the voltage at BAT. However, if the voltage at BAT

is below 3.3V, and the load requirement does not cause

the switching regulator to exceed its current limit, VOUT

will regulate at a ﬁxed 3.6V, as shown in Figure 2. This

instant-on operation will allow a portable product to run

immediately when power is applied without waiting for the

battery to charge. If the load does exceed the current limit

at VBUS, VOUT will range between the no-load voltage and

slightly below the battery voltage, indicated by the shaded

region of Figure 2.

Figure 1. Power Path Block Diagram – Power Available from USB/Wall Adapter

–

0.3V

1.18V

3.6V

CLPROG

ISWITCH/N

+ –

15mV

OmV

IDEAL

DIODE

PWM AND

GATE DRIVE

AVERAGE VBUS INPUT

CURRENT LIMIT

CONTROLLER

VBUS

VOLTAGE

CONTROLLER

VOUT VOLTAGE

CONTROLLER

IDGATE

VOUT

3.5V TO

(BAT + 0.3V)

TO SYSTEM LOAD

SINGLE CELL

Li-Ion

41601 F01

BAT

USB INPUT

BATTERY POWER

TO USB

OR WALL

ADAPTER

VBUS

OVERVOLTAGE PROTECTION

–

BATTERY CHARGER

IBAT/1000

VFLOAT

PROG

OVSENS

OVGATE

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