e7804 Semtech Corporation, e7804 Datasheet - Page 7

• Manufacturer Part Number: e7804
• Description: 133 Mhz Quad Pin Electronics Driver And Window Comparator
• Manufacturer: Semtech Corporation

Driver Connect/Disconnect
The driver output connects to the VIO output pin through an
internal, normally open switch (S). Refer to the Functional
Block diagram in Figure  for Switch S. This switch can
be closed by serially programming the internal register bit
for the appropriate channel (see Table 2, CH[0:3]_Relays_
&_States registers) denoted as S to a logical “”. Logical
“0” will open the switch. An external pin, OPN[0:3] one
input for each channel, is combined with the register bit
and will override the internal register bit and Open the S
switch for the channel. In its low state, the OPN input will
not override and force the switch closed however. (It should
be noted that OPN= will also open S2 to disconnect the
channel’s window comparators from the VIO pin.) OPN is
a fast way of disconnecting the lower voltage driver and
comparator circuitry from the VIO pin. When the driver (and
comparator) are disconnected, the voltage at VIO may be
in the range of the VEE to VXX power supplies.
The high voltage disconnect switches permit an external
Parametric Measurement Unit (PMU) to be connected to
the VIO pin having a maximum range from VEE to VXX volts
and up to ±40 mA.
This high voltage isolation also permits an external driver to
apply up to VXX volts (when switches S and S2 are open)
for high voltage applications.
Each driver may also be connected, internally, to EPMUS
in order to measure its output for purposes of calibrating
the DVH/L levels via switch S3.
TEST AND MEASUREMENT PRODUCTS
Circuit Description (continued)
OPN
DVL
DVH
HiZ
©
2007 Semtech Corp. / Rev. 7, 02/26/07
DEN
1
1
0
0
Digital Inputs
(Open Channel
Input)
(Driver Low)
(Driver High)
(High Impedance)
Table 1. Driver Modes of Operation
DHI
0
1
0
1
S1 Closed
Open
X
S1
DVH
DVL
VIO
HiZ
HiZ
OPN=0
(Driver, Comp open/discon-
nected (see Table 3)
(Don’t Care)
(Driver Output Switch
S1 Open
Open
Open
Open
Open
VIO
OPN=1
Open
Open
Open
Open
VIO
X
Comparator
Each channel’s two comparators, A and B, are combined to
form a window comparator to determine whether its input,
VINP, is above, below, or in between the two comparator
thresholds (CVA and CVB). VINP is tied to the positive input
of both comparators.
The CVA/B inputs should be driven from low impedance
sources. There is an input non-linear current shift of ~5µA
when the VINP signal to the comparator crosses polarity
with respect to the CVA/B input. If the source impedance
is too great, this could affect the accuracy of the compare
points. The voltage source’s output impedance should
be below 4KW to avoid this. DAC or op amp outputs will
have no issue with this. (If resistor dividers are used to
create the CVA/B voltages, the voltage should be buffered
to prevent this shift.)
VINP has a range of –2V, +5.5V, but is restricted to the
range of the drivers whenever a comparator is connected
to its driver (S and S2 switches both closed), namely
–0.2V, +5.2V.
The comparator outputs are differential LVDS compatible
on the QA/QA* and QB/QB* device pins. The output
states of the comparators for each channel can also
be read back using the serial interface. See Table 3,
CH[0:3]_switches_&_states read back instruction for the
individual channels.
Comparator Levels
Each channel’s CVA and CVB are the window comparator’s
two threshold levels. CVA and CVB are high impedance
voltage inputs that determine the thresholds at which the
window comparator changes state. CVA and CVB have a
range of –2.0V, +5.5V.
Comparator Connect/Disconnect
The window comparator input (VINP) connects to the
VIO pin through an internal switch (S2). This switch can
be closed to VIO by serially programming the internal
register bit for the appropriate channel (see Table 2,
CH[0:3]_switches_&_states registers) denoted as S2 to a
logical “”. Logical “0” will open the switch from VIO. The
comparator input is connected to approximately zero volts
7
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E7804