LTC4098EUDC-3.6 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4098EUDC-3.6

USB Compatible Switching Power Manager/LiFePO4 Charger with Overvoltage Protection

Linear Technology 

LTC4098-3.6

OPERATION

The input current limit is programmed by various com-

binations of the D0, D1 and D2 pins as shown in Table 1.

The switching input regulator can also be deactivated

(USB suspend).

The average input current will be limited by the CLPROG

programming resistor according to the following

expression:

( ) IVBUS

=

IVBUSQ

+

VCLPROG

RCLPROG

•

hCLPROG + 1

where IVBUSQ is the quiescent current of the LTC4098‑3.6,

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 current 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 1x

or 5x mode will not be violated, provided that RCLPROG is

3.01k or greater.

Table 1 shows the available settings for the D0, D1 and

D2 pins.

Table 1. Controlled Input Current Limit

CHARGER

D2

D1

D0

STATUS

0

0

0

On

0

0

1

On

0

1

0

On

0

1

1

Off

1

0

0

Off

1

0

1

Off

1

1

0

Off

1

1

1

Off

IBUS(LIM)

100mA (1x)

1A (10x)

500mA (5x)

500µA (Susp Low)

100mA (1x)

1A (10x)

500mA (5x)

2.5mA (Susp High)

Notice that when D0 is high and D1 is low, the switching

regulator is set to a higher current limit for increased

charging and power availability at VOUT. These modes will

typically be used when there is line power available from

a wall adapter.

While not in current limit, the switching regulator’s

Bat-Track feature will set VOUT to approximately 400mV

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

is below 3.1V, and the load requirement does not cause

the switching regulator to exceed its current limit, VOUT

will regulate at a fixed 3.5V, 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.

4.0

3.8

3.6 NO LOAD

3.4

3.2

400mV

3.0

2.8

2.6

2.4

2.4

2.7

3.0

3.3

3.6

BAT (V)

409836 F02

Figure 2. VOUT vs BAT

409836f

14

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