E142AHF Datasheet, PDF (8/19 Pages) Semtech Corporation – Per Pin timing Deskew w 4x2 Cross Point Switch

Edge142
EDGE HIGH-PERFORMANCE PRODUCTS
Circuit Description (continued)
Analog Delay Inputs
Compensation Pins
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).
COMP1 and COMP2 are Op Amp compensation pins.
For proper Edge142 functionality, these pins require a
.1 µF capacitor to ground.
VMID should be permanently set to the middle of the
overall voltage range spanned by VFALL (~ -0.6V). A
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 KΩ), 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.
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.
TDP
Bias 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.
˚ ^{Temperature coefficient = –10 mV/ C}
TDN
Figure 6. Thermal Diode String
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.
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).
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.
 2000 Semtech Corp.
8
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