Datasheet

Output Stage Circuitry
The MAX961–MAX964/MAX997/MAX999 contain a cur-
rent-driven output stage, as shown in Figure 4. During an
output transition, I
SOURCE
or I
SINK
is pushed or pulled to
the output pin. The output source or sink current is high
during the transition, creating a rapid slew rate. Once the
output voltage reaches V
OH
or V
OL
, the source or sink
current decreases to a small value, capable of maintain-
ing the V
OH
or V
OL
in static condition. This decrease in
current conserves power after an output transition has
occurred.
One consequence of a current-driven output stage is a
linear dependence between the slew rate and the load
capacitance. A heavy capacitive load slows down the volt-
age output transition.
Shutdown Mode
When SHDN is high, the MAX961/MAX963/MAX964/
MAX997 shut down. When shut down, the supply current
drops to 270μA per comparator, and the outputs become
high impedance. SHDN has a high input impedance.
Connect SHDN to GND for normal operation. Exit shut-
down with LE low; otherwise, the output is indeterminate.
Applications Information
Circuit Layout and Bypassing
The MAX961–MAX964/MAX997/MAX999’s high band-
width requires a high-speed layout. Follow these layout
guidelines:
1) Use a PCB with a good, unbroken, low-inductance
ground plane.
2) Place a decoupling capacitor (a 0.1μF ceramic sur-
face-mount capacitor is a good choice) as close to
V
CC
as possible.
3) On the inputs and outputs, keep lead lengths short to
avoid unwanted parasitic feedback around the com-
parators. Keep inputs away from outputs. Keep imped-
ance between the inputs low.
4) Solder the device directly to the printed circuit board
rather than using a socket.
5) Refer to Figure 5 for a recommended circuit layout.
6) For slow-moving input signals, take care to prevent
parasitic feedback. A small capacitor (1000pF or less)
placed between the inputs can help eliminate oscil-
lations in the transition region. This capacitor causes
negligible degradation to t
PD
when the source imped-
ance is low.
Figure 4. Output Stage Circuitry Figure 5. MAX961 PCB Layout
MAX961–MAX964
MAX997
MAX999
I
SOURCE
Q, Q
V
CC
GND
I
SINK
MAX961–MAX964/
MAX997/MAX999
Single/Dual/Quad, Ultra-High-Speed, +3V/+5V,
Beyond-the-Rails Comparators
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