TS9001 datasheet(7/8 Pages) TOUCHSTONE

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TS9001

TS9001DS r1p0

Page 7

RTFDS

6) The last step is to verify the trip voltages and

hysteresis band using the standard

resistance values:

For VIN rising:

VTHR = VREF x R1 [(1/R1) + (1/R2) + (1/R3)]

= 3V

For VIN falling:

VTHF = VTHR - (R1 x VCC/R2) = 2.9V

and Hysteresis Band = VTHR – VTHF = 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 VCC as shown in

Figure 4. Additional hysteresis can be generated

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 = VREF/0.2µA

R2 = (VCC - VREF)/0.2μA - R4

where the smaller of the two resulting

resistor values is the best starting value.

2) As before, the desired hysteresis band

(VHYSB) is set to 100mV.

3) Next, resistor R1 is then computed

according to the following equation:

R1 = (R2 + R4) x (VHYSB/VCC)

4) The trip point for VIN rising (VTHR) is chosen

(again, remember that 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.

5) With the VTHR from Step 4 above, resistor R3

is computed as follows:

R3 = 1/[VTHR/(VREF 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 VIN rising:

VTHR = VREF x R1 x (1/R1+1/R2+1/R3)

For VIN falling:

VTHF = VREF x R1 x (1/R1+1/R3+1/(R2+R4))

-(R1/(R2+R4)) x VCC

and Hysteresis Band is given by VTHR - VTHF

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.

Figure 4

: Using Four Resistors Introduces Additional

Hysteresis in the TS9001-2.

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