E142AHF datasheet(8/19 Pages) SEMTECH

8 / 19 page

 2000 Semtech Corp.

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EDGE HIGH-PERFORMANCE PRODUCTS

Edge142

Circuit Description (continued)

Analog Delay Inputs

VDELAY, VFALL, and VMID are analog voltage inputs which

control the delay of the rising and falling edge. All three

inputs may vary from +0.1V (minimum delay) to -1.3V

(maximum delay).

VMID should be permanently set to the middle of the

overall voltage range spanned by VFALL (~ -0.6V).

fixed resistor to ground will usually suffice. The exact

setting of VFALL will vary depending on the required delay

range of the falling edge.

These inputs are designed to sink a constant input

current, typically 1.0 mA (with REXT1 = 2.94 K

Ω), over

their operating range from +0.1V to -1.3V. Any voltage

DAC used to drive these inputs directly needs to source

at least 1.0 mA. Any current DAC used needs to factor

in the constant 1.0 mA input current.

The equation used to establish the VDELAY, VMID, and

VFALL input currents is:

I (VFALL, VDELAY, VMID) = 3.0V / REXT1.

The fact that the VDELAY, VFALL, and VMID inputs have

internal current sources allows a voltage DAC capable

of generating only positive voltages and an external

resistor network to be pulled down to the Edge142's

negative input voltage compliance.

These current

sources are designed to be constant over temperature,

so changes in system temperature will not translate into

a delay voltage shift.

Using a different REXT1 will program a different input

current.

However, the value of this current does not

affect deskew range or performance. The ability to vary

this current allows a more flexible interface to a variety

of DAC programming techniques.

VDELAY, VFALL, and VMID all require current flow. Do

NOT leave any of these input pins floating.

If an

application does not require any falling edge delay,

connect all VDELAY and VMID pins to ground.

Compensation Pins

COMP1 and COMP2 are Op Amp compensation pins.

For proper Edge142 functionality, these pins require a

µF capacitor to ground.

Thermal Monitor

The Edge142 includes an on-chip thermal monitor

accessible through the pins TDP and TDN. These nodes

connect to five diodes in series (see Figure 6) and may

be used to accurately measure the junction temperature

at any time.

Figure 6. Thermal Diode String

An external bias current of 100

µA is injected through

the string, and the measured voltage corresponds to a

specific junction temperature with the following equation:

TJ(˚C) = {(V(TDP) – V(TDN)) / 5 – .7} / (-.00208).

Bias Current

Temperature coefficient = –10 mV/˚C

TDP

TDN

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