EL6204 데이터 시트보기 (PDF) - Intersil

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EL6204

Laser Driver Oscillator

Intersil 

EL6204

Supply Bypassing and Grounding

The resistance of bypass-capacitors and the inductance of

bonding wires prevent perfect bypass action, and 150mVP-P

noise on the power lines is common. There needs to be a

lossy bead inductance and secondary bypass on the supply

side to control signals from propagating down the wires.

Figure 2 shows the typical connection.

L Series: 70Ω reactance at 300MHz

VS

EL6204

GND

0.1µF

Chip

+5V

0.1µF

Chip

FIGURE 2. RECOMMENDED SUPPLY BYPASSING

Also important is circuit-board layout. At the EL6204's

operating frequencies, even the ground plane is not low-

impedance. High frequency current will create voltage drops

in the ground plane. Figure 3 shows the output current loops.

RFREQ

RAMP

Supply

Bypass

Sourcing Current Loop

GND

Sinking Current Loop

Laser

Diode

FIGURE 3. OUTPUT CURRENT LOOPS

For the pushing current loop, the current flows through the

bypass capacitor, into the EL6204 supply pin, out the IOUT

pin to the laser, and from the laser back to the decoupling

capacitor. This loop should be small.

For the pulling current loop, the current flows into the IOUT

pin, out of the ground pin, to the laser cathode, and from the

laser diode back to the IOUT pin. This loop should also be

small.

Power Dissipation

With the high output drive capability, the EL6204 is possible

to exceed the 125°C “absolute-maximum junction

temperature” under certain conditions. Therefore, it is

important to calculate the maximum junction temperature for

the application to determine if the conditions need to be

modified for the oscillator to remain in the safe operating

area.

The maximum power dissipation allowed in a package is

determined according to:

PDMAX

=

T----J---M-----A----X-----------T----A----M-----A---X--

ΘJA

where

PDMAX = Maximum power dissipation in the package

TJMAX = Maximum junction temperature

TAMAX = Maximum ambient temperature

θJA = Thermal resistance of the package

The supply current of the EL6204 depends on the peak-to-

peak output current and the operating frequency which are

determined by resistors RAMP and RFREQ. The supply

current can be predicted approximately by the following

equation:

ISUP

=

3----1---.--2---5----m-----A------×-----1----k---Ω---

RAMP

+

-3---0----m-----A------×----1----k----Ω---

RFREQ

+

0.6

m

A

The power dissipation can be calculated from the following

equation:

PD = VSUP × ISUP

Here, VSUP is the supply voltage. Figures 4 and 5 provide a

convenient way to see if the device will overheat. The

maximum safe power dissipation can be found graphically,

based on the package type and the ambient temperature. By

using the previous equation, it is a simple matter to see if PD

exceeds the device's power derating curve. To ensure

proper operation, it is important to observe the

recommended derating curve shown in Figures 4 and 5. A

flex circuit may have a higher θJA, and lower power

dissipation would then be required.

Package Power Dissipation vs Ambient Temperature

JEDEC JESD51-3 Low Effective Thermal Conductivity Test Board

0.6

0.5

488mW

0.4

0.3

θJA 6=-2P5i6n°CS/OWT-23

0.2

0.1

0

0

25

50

75 85 100

125

150

Ambient Temperature (°C)

FIGURE 4. PACKAGE POWER DISSIPATION vs

AMBIENT TEMPERATURE

9

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