10

FN7333.3

For noise sensitive application, a 0.1µF placed in parallel

with the larger output capacitor is recommended to reduce

the switching noise coupled from the LX switching node.

Schottky Diode

In selecting the Schottky diode, the reverse break down

voltage, forward current and forward voltage drop must be

considered for optimum converter performance. The diode

must be rated to handle 1.5A, the current limit of the

EL7516. The breakdown voltage must exceed the maximum

output voltage. Low forward voltage drop, low leakage

current, and fast reverse recovery will help the converter to

achieve the maximum efficiency.

Input Capacitor

The value of the input capacitor depends the input and

output voltages, the maximum output current, the inductor

value and the noise allowed to put back on the input line. For

most applications, a minimum 10µF is required. For

applications that run close to the maximum output current

limit, input capacitor in the range of 22µF to 47µF is

recommended.

pin to reduce supply line noise and ensure stable operation.

Loop Compensation

The EL7516 incorporates an transconductance amplifier in

its feedback path to allow the user some adjustment on the

transient response and better regulation. The EL7516 uses

current mode control architecture which has a fast current

sense loop and a slow voltage feedback loop. The fast

current feedback loop does not require any compensation.

The slow voltage loop must be compensated for stable

operation. The compensation network is a series RC

network from COMP pin to ground. The resistor sets the high

frequency integrator gain for fast transient response and the

capacitor sets the integrator zero to ensure loop stability. For

most applications, the compensation resistor in the range of

2K to 7.5K and the compensation capacitor in the range of

3nF to 10nF.

Soft-Start

The soft-start is provided by an internal 6µA current source

limited by the voltage on the capacitor. This in turn controls

the rising rate of the output voltage. The regulator goes

through the start-up sequence as well after the SHDN pin is

pulled to HI.

Frequency Selection

The EL7516 switching frequency can be user selected to

operate at either at constant 620kHz or 1.25MHz.

switching frequency is set to 1.25MHz.

Shut-Down Control

When shut-down in is pulled low, the EL7516 is shut-down

reducing the supply current to <3µA.

Maximum Output Current

The MOSFET current limit is nominally 1.5A and guaranteed

based on the following formula:

where:

D = MOSFET turn-on ratio:

The following table gives typical maximum Iout values for

1.2MHz switching frequency and 22µH inductor:

Thermal Performance

The EL7516 uses a fused-lead package, which has a

reduced

on a two-layer board. Maximizing copper around the ground

pins will improve the thermal performance.

This device also has internal thermal shut-down set at

around 130°C to protect the component.

TABLE 1.

2.5

5

570

2.5

9

325

2.5

12

250

3.3

5

750

3.3

9

435

3.3

12

330

5

9

650

5

12

490

⁄∆I

L

×

()

+

=

∆I

L

+

() V

IN

–

[]

×

(

×

+

×

------------------------------------------------------------------------------

=

1D

–

-------------

=

D1

+

--------------------------------------------

–

=

EL7516