ISL1539IRZ Datasheet, PDF (10/11 Pages) Intersil Corporation – Dual Channel Differential VDSL2 Line Driver

ISL1539
where:
• T_JUNCT is the maximum die temperature (+150°C)
• T_AMB is the maximum ambient temperature
• P_DISS is the dissipation calculated above
• θ_JA is the junction to ambient thermal resistance for the
package when mounted on the PCB
This θ_JA value is then used to calculate the area of copper
needed on the board to dissipate the power.
The IRE and QFN power packages are designed so that heat may
be conducted away from the device in an efficient manner. To
disperse this heat, the bottom diepad is internally connected to
the mounting platform of the die. Heat flows through the diepad
into the circuit board copper, then spreads and convects to air.
Thus, the ground plane on the component side of the board
becomes the heatsink. This has proven to be a very effective
technique. θ_JA of +30°C/W can be achieved.
Single Supply Operation
The ISL1539 can also be powered from a single supply voltage.
When operating in this mode, the GND pins can still be
connected directly to GND. To calculate power dissipation, the
equations in the previous section should be used, with V_S equal
to half the supply rail.
Output Loading
While the drive amplifiers can output in excess of 450mA
transiently, the internal metallization is not designed to carry
more than 75mA of steady DC current and there is no
current-limit mechanism. This allows safely driving rms
sinusoidal currents of 2mAx75mA, or 150mA. This current is
more than that required to drive line impedances to large output
levels, but output short circuits cannot be tolerated. The series
output resistor will usually limit currents to safe values in the
event of line shorts. Driving lines with no series resistor is a
serious hazard.
Power Supplies
The power supplies should be well bypassed close to the
ISL1539. A 3.3µF tantalum capacitor for each supply works well.
Since the load currents are differential, they should not travel
through the board copper and set up ground loops that can
return to amplifier inputs. Due to the class AB output stage
design, these currents have heavy harmonic content. If the
ground terminal of the positive and negative bypass capacitors
are connected to each other directly and then returned to circuit
ground, no such ground loops will occur. This scheme is
employed in the layout of the EL1537 demonstration board, and
documentation can be obtained from the factory.
Power Control Function
The ISL1539 contains two forms of power control operation. Two
digital inputs, C₀ and C₁, can be used to control the supply
current of the ISL1539 drive amplifiers. As the supply current is
reduced, the ISL1539 will start to exhibit slightly higher levels of
distortion and the frequency response will be limited. The four
power modes of the ISL1539 are set up as shown in the table1
below.
TABLE 1. POWER MODES OF THE EL15371
C₁
C₀
Operation
0
0
I_S Full Power Mode
0
1
3/4-I_S Power Mode
1
0
1/2-I_S Power Mode
1
1
Power Down
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FN7516.4
June 21, 2013