Datasheet
Hysterisis Adjust
R
HYS
+
26.1 H
HYS
0.365
ǒ
1 * V
HYS
Ǔ
kW
(2)
Threshold Adjust
R
THD
+
39.2 kW
39.2
ƪ
(1ńR
HYS
) 0.014
Ǔ
ǒ
V
THD
ń2.5 * 1
Ǔ
* 0.0027
ƫ
*1
(3)
Calculated Values
PTH12040W
SLTS237G – DECEMBER 2004 – REVISED MARCH 2009 ...............................................................................................................................................
www.ti.com
The hysterisis voltage, V
HYS,
is the difference between the on and off threshold values. The default value is 1 V
and it can only be adjusted to a lower value.
Caution should be used when changing the hysterisis voltage to a lower value, as it could induce
start-up oscillations.
Any change in the hysterisis voltage requires both R
HYS
and R
THD
resistors be in place. Adding R
HYS
alone does
not have the desired effect. The value for R
HYS
must first be calculated using Equation 2 . The value identified for
R
HYS
must then be used to determine a value for R
THD
, using Equation 3 .
Equation 3 determines the value of R
THD
required to adjust V
THD
to a new value. The default value is 7.5 V, and it
may only be adjusted to a higher value. If the hysterisis value has been adjusted, then a value for R
THD
must also
be calculated. (This is irrespective of whether V
THD
is being adjusted.) If there has been no adjustment for the
hystersis voltage, the term 1/R
HYS
in Equation 3 , may be assigned the value, 0.
Table 4 shows a matrix of standard resistor values for R
HYS
and R
THD
, for different options of the on-threshold
(V
THD
) and hysterisis (V
HYS
) voltages. For most applications, only the on-threshold voltage should need to be
adjusted. In this case select only a value for R
THD
from far right-hand column.
The hysterisis should only be adjusted if there is a specific requirement to independently adjust the off-threshold,
separately from the on-threshold voltage. In this case, a value for both R
HYS
and R
THD
must be selected from
Table 4 . This is irrespective of whether the on-threshold voltage is being adjusted.
Table 4. Calculated Values of R
HYS
and R
THD
, for Various Values of V
HYS
and
V
THD
1 V
V
HYS
0.5 V 0.6 V 0.7 V 0.8 V 0.9 V
(default)
V
THD
(V) R
HYS
( k Ω ) 71.5 107 165 287 649.0 N/A
8.0 30.1 43.2 63.4 97.6 169 .0 402.0
8.5 25.5 36.5 51.1 73.2 110.0 187.0
9.0 23.2 30.9 42.2 57.6 82.5 124.0
9.5 20.0 27.4 36.5 48.7 64.9 90.9
10.0 R
THD
( k Ω ) 18.2 24.3 31.6 41.2 54.9 73.2
10.5 16.2 21.5 28.0 36.5 46.4 60.4
11.0 15.0 19.6 25.5 32.4 41.2 52.3
11.5 14.0 18.2 23.2 28.0 36.5 45.3
12.0 12.7 16.5 21.0 26.1 32.4 40.2
14 Submit Documentation Feedback Copyright © 2004 – 2009, Texas Instruments Incorporated
Product Folder Link(s): PTH12040W