ISL58792

11

FN7580.3

December 14, 2015

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Applications Information

The data sheet values for oscillator current, and write current are

needs of the application.

“Typical Performance Curves” on page 11.

The write channel output capability for a typical part is shown in

A four input DAC (Reg 1-0A bits 3, 2, 1, 0) can be used to control

the amount of RC snubbing applied to the outputs. For IBLUE,

there is an extra bit (Reg 1-0A bit 4) weighted as MSB.

Read current may be controlled by either the Read DAC or the

together.

Glitches could occur if two or three WEN lines are changed

simultaneously, and the propagation delay is different for the two

lines between the inner circuits of the controller and the inner

circuits of the LDD. Because the WEN lines are encoded, the

selected write current will be correct before the change in code,

and again after the code changes. But some other output could

result momentarily if the propagation delays are not matched.

The skew detector detects the first rising edge at the LVDS

outputs.

desired range or operating point of the HFMFREQ DAC. Although

guaranteed (see Figures 5 and 6).

The oscillator may be turned on by the WEN code selected. The

particular code that selects the oscillator is under program

control and WEN selection.

The WEB enables write current. WEN code 000 through 111 will

select a write current as described in Table 1.

Power

The main power consumption is caused by the headroom voltage

headroom voltage is available to obtain the desired output

current. For the blue outputs, the built in ADC can be used to

obtain the output voltage, which is also the headroom voltage.

The HFM oscillator power consumption will increase with

increasing frequency and amplitude (see Figure 7).

Note that in the TQFN package, the die is mounted directly on the

thermal pad. This provides a very low thermal resistance Junction

to thermal pad of just a few °C/W. The problem is in moving the

heat from the thermal pad to some other heat sink.

Figure 12 shows that when mounted well on a 4-layer PCB with 3

ground plane layers, and an area of 10cmx10cm, the

+42°C/W. The typical application will not afford this good of a

heat sink.

Typical Performance Curves

(REG 1-21 = 88h) (VSO = 4.5V)

3FFh

300h

200h

100h

80h

40h

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

0

200

400

600

800

1000

1200

02

5

7

13

46

8

3FFh

300h

200h

100h

40h

001h

0

100

200

300

400

500