TS9001
out of the region where oscillation occurs. Figure 2
illustrates the case in which an IN- input is a fixed
voltage and an IN+ is varied. If the input signals
were reversed, the figure would be the same with an
inverted output. To save cost and external pcb area,
an internal 4mV hysteresis circuit was added to the
TS9001-1/2.
point is (VREF - VOUT)/R2.
In solving for R2, there are two formulas –
one each for the two possible output states:
R2 = VREF/IR2
or
R2 = (VCC - VREF)/IR2
From the results of the two formulae, the
smaller of the two resulting resistor values is
chosen. For example, when using the
TS9001-1 (VREF = 1.252V) at a VCC = 3.3V
and if IR2 = 0.2μA is chosen, then the
formulae above produce two resistor values:
6.26Mꢀ and 10.24Mꢀ - the 6.2Mꢀ standard
value for R2 is selected.
2) Next, the desired hysteresis band (VHYSB) is
set. In this example, VHYSB is set to 100mV.
Figure 2: TS9001 Threshold Hysteresis Band
Adding Hysteresis to the TS9001-1 Push-pull
Output Option
3) Resistor R1 is calculated according to the
following equation:
The TS9001-1 exhibits an internal hysteresis band
(VHYSB) of 4mV. Additional hysteresis can be
R1 = R2 x (VHYSB/VCC)
and substituting the values selected in 1)
and 2) above yields:
R1 = 6.2Mꢀ x (100mV/3.3V) = 187.88kꢀ.
The 187kꢀ standard value for R1 is chosen.
4) The trip point for VIN rising (VTHR) is chosen
such that VTHR > VREF x (R1 + R2)/R2 (VTHF
is the trip point for VIN falling). This is the
threshold voltage at which the comparator
switches its output from low to high as VIN
rises above the trip point. In this example,
VTHR is set to 3V.
Figure 3: Using Three Resistors Introduces
Additional Hysteresis in the TS9001-1.
5) With the VTHR from Step 4 above, resistor R3
is then computed as follows:
generated with three external resistors using positive
feedback as shown in Figure 3. Unfortunately, this
method also reduces the hysteresis response time.
The procedure to calculate the resistor values for the
TS9001-1 is as follows:
R3 = 1/[VTHR/(VREF x R1) - (1/R1) - (1/R2)]
R3 = 1/[3V/(1.252V x 187kꢀ)
- (1/187kꢀ) - (1/6.2Mꢀ)] = 136.9kꢀ
1) Setting R2. As the leakage current at the IN
pin is less than 2nA, the current through R2
should be at least 0.2μA to minimize offset
voltage errors caused by the input leakage
current. The current through R2 at the trip
In this example, a 137kꢀ, 1% standard
value resistor is selected for R3..
Page 6
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