TS9001
6) The last step is to verify the trip voltages and
hysteresis band using the standard
resistance values:
For V
IN
rising:
V
THR
= V
REF
x R1 [(1/R1) + (1/R2) + (1/R3)]
= 3V
For V
IN
falling:
V
THF
= V
THR
- (R1 x V
CC
/R2) = 2.9V
and Hysteresis Band = V
THR
– V
THF
= 100mV
Adding Hysteresis to the TS9001-2 Open-Drain
Option
The TS9001-2 has open-drain output and requires
an external pull-up resistor to V
CC
as shown in
Figure 4. Additional hysteresis can be generated
where the smaller of the two resulting
resistor values is the best starting value.
2) As before, the desired hysteresis band
(V
HYSB
) is set to 100mV.
3) Next, resistor R1 is then computed
according to the following equation:
R1 = (R2 + R4) x (V
HYSB
/V
CC
)
4) The trip point for V
IN
rising (V
THR
) is chosen
(again, remember that V
THF
is the trip point
for V
IN
falling). This is the threshold voltage
at which the comparator switches its output
from low to high as V
IN
rises above the trip
point.
5) With the V
THR
from Step 4 above, resistor R3
is computed as follows:
R3 = 1/[V
THR
/(V
REF
x R1) - (1/R1) - (1/R2)]
6) As before, the last step is to verify the trip
voltages and hysteresis band with the
standard resistor values used in the circuit:
For V
IN
rising:
V
THR
= V
REF
x R1 x (1/R1+1/R2+1/R3)
For V
IN
falling:
V
THF
= V
REF
x R1 x (1/R1+1/R3+1/(R2+R4))
-(R1/(R2+R4)) x V
CC
Figure 4:
Using Four Resistors Introduces Additional
Hysteresis in the TS9001-2.
using positive feedback; however, the formulae differ
slightly from those of the push-pull option TS9001-1.
The procedure to calculate the resistor values for the
TS9001-2 is as follows:
1) As in the previous section, resistor R2 is
chosen according to the formulae:
R2 = V
REF
/0.2µA
or
R2 = (V
CC
- V
REF
)/0.2μA - R4
and Hysteresis Band is given by V
THR
- V
THF
PC Board Layout and Power-Supply Bypassing
While power-supply bypass capacitors are not
typically required, it is good engineering practice to
use 0.1uF bypass capacitors close to the device’s
power supply pins when the power supply
impedance is high, the power supply leads are long,
or there is excessive noise on the power supply
traces. To reduce stray capacitance, it is also good
engineering practice to make signal trace lengths as
short as possible. Also recommended are a ground
plane and surface mount resistors and capacitors.
TS9001DS r1p0
Page 7
RTFDS
TOUCHSTONE [ TOUCHSTONE SEMICONDUCTOR INC ]
