LTH2 Marking, LT3465 datasheet(16/24 Pages) LINER

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LT3498

3498f

Maximum Output Load Current

The maximum output current of a particular LT3498

circuit is a function of several circuit variables. The fol-

lowing method can be helpful in predicting the maximum

load current for a given circuit:

Step 1: Calculate the peak inductor current:

amps

LIMIT

••

–

400 10

where ILIMIT is 0.3A for the OLED driver. L is the induc-

tance value in Henrys and VIN is the input voltage to the

boost circuit.

Step 2: Calculate the inductor ripple current:

amps

RIPPLE

OUT

()

150 10

–•

•

–

where VOUT2 is the desired output voltage.

If the inductor ripple current is less then the peak current,

then the circuit will only operate in discontinuous conduc-

tion mode. The inductor value should be increased so

that IRIPPLE < IPK. An application circuit can be designed

to operate only in discontinuous mode, but the output

current capability will be reduced.

Step 3: Calculate the average input current:

amps

IN AVG

RIPPLE

()

–

Step 4: Calculate the nominal output current:

amps

OUT NOM

IN AVG

OUT

()

() •• .

075

Step 5: Derate output current:

IOUT = IOUT(NOM) • 0.7 amps

For low output voltages the output current capability will

be increased. When using output disconnect (load current

taken from VOUT2), these higher currents will cause the

drop in the PMOS switch to be higher resulting in reduced

output current capability than those predicted by the

preceding equations.

Inrush Current

When VIN is stepped from ground to the operating voltage

while the output capacitor is discharged, a higher level of

inrush current will ﬂow through the inductor and integrated

Schottky diode into the output capacitor. Conditions that

increase inrush current include a larger more abrupt voltage

step at VIN, a larger output capacitor tied to the CAP2 pin,

and an inductor with a low saturation current. While the

internal diode is designed to handle such events, the inrush

current should not be allowed to exceed 1A. For circuits

that use output capacitor values within the recommended

range and have input voltages of less than 5V, inrush cur-

rent remains low, posing no hazard to the device. In cases

where there are large steps at VIN (more than 5V) and/or

a large capacitor is used at the CAP2 pin, inrush current

should be measured to ensure safe operation.

APPLICATIONS INFORMATION— OLED DRIVER

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