TSM921 TOUCHSTONE [Touchstone Semiconductor Inc], TSM921 Datasheet - Page 12

• Manufacturer Part Number: TSM921
• Description: Ultra-Low-Power, Single/Dual-Supply Comparators
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

TSM921-TSM924
THEORY OF OPERATION
The TSM921–TSM924 family of single/dual/quad,
low-voltage,
provide excellent flexibility and performance while
sourcing continuously up to 40mA of current. The
TSM921, TSM923, and the TSM924 provide an
on-board
minimize glitches that can occur with parasitic
feedback or due to less than optimal board layout,
the design of the TSM921-TSM924 output stage is
optimized to eliminate crowbar glitches as the output
switches. To minimize current consumption while
providing flexibility, the TSM921 and the TSM923
have an on-board HYST pin in order to add
additional hysteresis.
Power-Supply and Input Signal Ranges
The TSM921-TSM924 can operate from a single
supply voltage range of +2.5V to +11V, provide a
wide common mode input voltage range of V- to
V+-1.3V, and accept input signals ranging from V- to
V+ - 1V. The inputs can accept an input as much as
300mV above and below the power supply rails
without damage to the part. While the TSM921 and
the TSM924 are able to operate from a single supply
voltage range, a GND pin is available that allows for
a dual supply operation with a range of ±1.25V to
±5.5V. If a single supply operation is desired, the
GND pin needs to be tied to V-. In a dual supply
mode, the TSM921 and the TSM924 are TTL/CMOS
compatible with a ±5V voltage and the TSM922 and
the TSM923 are TTL compatible with a single +5V
supply.
Low-Voltage Operation: V+ = 1.5V (TSM924 Only)
Due to a decrease in propagation delay and a
reduction in output drive, the TSM921-TSM923
cannot be used with a supply voltage much lower
than 2.5V. However, the TSM924 can operate down
to a supply voltage of 2V; however, as the supply
voltage reduces, the TSM924 supply current drops
and the performance is degraded. When the supply
voltage drops to 2.2V, the reference voltage will no
longer function; however, the comparators will
function
Furthermore, the input voltage range is extended to
just below 1.5V the positive supply rail. For
applications with a sub-2.5V power supply, it is
Page 12
down
1.182V
micropower
to
±1%
a
reference
1.5V
analog
supply
voltage.
comparators
voltage.
To
recommended to evaluate the circuit over the entire
power supply range and temperature.
Comparator Output
The TSM921 and the TSM924 have a GND pin that
allows the output to swing from V+ to GND while the
V- pin can be set to a voltage below GND as long as
the voltage difference between V+ and V- is within
11V. Having a different voltage on V- will not affect
the output swing. For TTL applications, V+ can be
set to +5V±10% and V- can be set anywhere
between 0V and -5V±10%. On the other hand, the
TSM922 and the TSM923 do not have a GND pin;
hence, for TTL applications, V+ needs to be set to a
+5V power supply and V- to 0V. Furthermore, the
output design of the TSM921-TSM924 can source
and sink more than 40mA and 5mA, respectively,
while simultaneously maintaining a quiescent current
in the microampere range. If the power dissipation of
the package is maintained within the max limit, the
output can source pulses of 100mA of current with
V+ set to +5V. In an effort to minimize external
component count needed to address power supply
feedback, the TSM921-TSM924 output does not
produce crowbar switching current as the output
switches. With a 10mV input overdrive, the
propagation delay of the TSM921-TSM924 is 12μs.
Voltage Reference
The TSM921, TSM923, and TSM924 have an on-
board 1.182V reference voltage with an accuracy of
±1%. The REF pin is able to source and sink 15μA
and 8μA of current, respectively. The REF pin is
referenced to V- and it should not be bypassed.
Noise Considerations
Noise can play a role in the overall performance of
the TSM921-TSM924. Despite having a large gain, if
the input voltage is near or equal to the input offset
voltage, the output will randomly switch HIGH and
LOW. As a result, the TSM921-TSM924 produces a
peak-to-peak noise of approximately 0.3mV
the reference voltage produces a peak-to-peak
noise of approximately 1mV
important to design a layout that minimizes
capacitive coupling from a given output to the
reference pin as crosstalk can add noise and, as a
result, degrade performance.
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