TS12011/TS12012
falling). This is the threshold voltage at which
the comparator switches its output from low
to high as VCOMPIN+ rises above the trip point.
In this example, VTHR is set to 2.
5) With the VTHR from Step 4 above, resistor R3
is then computed as follows:
R3 = 1/[VTHR/(VREFOUT x R1) - (1/R1) - (1/R2)]
R3 = 1/[2V/(0.58V x 160kΩ) - (1/160kΩ) -
(1/4.02MΩ)] = 66.43kΩ
Figure 2. Using Three Resistors Introduces
Additional Hysteresis in the TS12011
In this example, a 69.8kΩ, 1% standard
value resistor is selected for R3.
1) Setting R2. As the leakage current at the IN
pin is less than 20nA, the current through R2
should be at least 150nA to minimize offset
voltage errors caused by the input leakage
current. The current through R2 at the trip
point is (VREFOUT - VCOMPOUT)/R2.
6) The last step is to verify the trip voltages and
hysteresis band using the standard
resistance values:
For VCOMPIN+ rising:
In solving for R2, there are two formulas –
one each for the two possible output states:
VTHR = VREFOUT x R1 [(1/R1) + (1/R2) + (1/R3)]
= 1.93V
R2 = VREFOUT/IR2
For VCOMPIN+ falling:
or
VTHF = VTHR - (R1 x VDD/R2) = 1.83V
and Hysteresis Band = VTHR – VTHF = 100mV
R2 = (VDD - VREFOUT)/IR2
From the results of the two formulae, the
smaller of the two resulting resistor values is
chosen. For example, when using the
TS12011 (VREFOUT = 0.58V) at a VDD = 2.5V
and if IR2 = 150nA is chosen, then the
formulae above produce two resistor values:
3.87MΩ and 12.8MΩ - a 4.02MΩ standard
value for R2 is selected.
2) Next, the desired hysteresis band (VHYSB) is
set. In this example, VHYSB is set to 100mV.
3) Resistor R1 is calculated according to the
following equation:
R1 = R2 x (VHYSB/VDD)
and substituting the values selected in 1) and
2) above yields:
R1 = 4.02MΩ x (100mV/2.5V) = 160.8kΩ.
The 160kΩ standard value for R1 is chosen.
4) The trip point for COMPIN+ rising (VTHR) is
chosen such that VTHR > VREFOUT x (R1 +
R2)/R2 (VTHF is the trip point for VCOMPIN+
Page 8
TS12011_12DS r1p0
RTFDS
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