pth12040 Astec Powe, pth12040 Datasheet - Page 10

• Manufacturer Part Number: pth12040
• Description: Pth12040 12vin Single
• Manufacturer: Astec Powe

7.2.3 Hysteresis Adjust
The Hysteresis voltage, V
‘off’ threshold values. The default value is 1V and it can only be
adjusted to a lower value.
! Caution should be used when changing the Hysteresis voltage to a
lower value, as it could induce start-up oscillations.
Any change in the Hysteresis voltage will require both R
resistors be in place. Adding R
effect. The value for R
The value identified for R
for R
7.2.4 Threshold Adjust
Equation 3 determines the value of R
new value. The default value is 7.5V, and it may only be adjusted to a
higher value. If the Hysteresis value has been adjusted, then a value
for R
V
hysteresis voltage, the term ‘1/R
the value, ‘0’.
7.2.5 Calculated Values
Table 6 shows a matrix of standard resistor values for R
R
(V
should need to be adjusted. In this case select only a value for R
from far right-hand column.
The Hysteresis 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 RHYS
and R
whether the on-threshold voltage is being adjusted.
THD
THD
HYS
1 1 0 0
THD
THD
, for different options of the on-threshold (V
is being adjusted.) If there has been no adjustment for the
) voltages. For most applications, only the on-threshold voltage
C
1,000µF
THD
i
, using Equation 3.
GND
must also be calculated. (This is irrespective of whether
must be selected from the table. This is irrespective of
Figure 8 - UVLO Program Resistor Placement
V
i
+
R
R
HYS
THD
HYS
HYS
HYS
must first be calculated using Equation 2.
, is the difference between the ‘on’ and
must then be used to determine a value
Equation 2
Equation 3
HYS
File Name: an_pth12040.pdf Rev (02): 21 Dec 2005
2
4
6
8
HYS’
V
UVLO Prog
Inhibit
alone will not have the desired
i
in Equation 3 may be assigned
THD
7
required to adjust V
PTH12040
GND
1 3 5
THD
) and Hysteresis
HYS
HYS
and
and R
THD
to a
THD
THD
7.3 Output ON/OFF Inhibit
For applications requiring output voltage ON/OFF control,each series
of the PTH family incorporates an output Inhibit control pin. The
inhibit feature can be used wherever there is a requirement for the
output voltage from the regulator to be turned OFF.
The power modules function normally when the Inhibit pin is left
open-circuit, providing a regulated output whenever a valid source
voltage is connected to V
typical application of the inhibit function. Note the discrete transistor
(Q1). The Inhibit control has its own internal pull-up to +Vin potential.
The input is not compatible with TTL logic devices. An open-
collector (or open-drain) discrete transistor is recommended for
control.
Turning Q1 on applies a low voltage to the Inhibit control pin and
disables the output of the module. If Q1 is then turned off, the
module will execute a soft-start power-up sequence. A regulated
output voltage is produced within 25ms. Figure 10 shows the typical
rise in both the output voltage and input current, following the turn-
off of Q1. The turn off of Q1 corresponds to the rise in the waveform,
Q1 V
1 = Inhibit
C
560µF
10.5V R
11.5V R
V
8.0V
8.5V
9.0V
9.5V
in
10V
11V
12V
V
GND
THD
in
DS
Figure 9 - Typical Application of the Inhibit Function
. The waveforms were measured with a 5A load.
+
V
R
R
R
R
R
R
R
R
Q1
BSS138
Table 6 - Calculated Values of R
HYS
HYS
THD
THD
THD
THD
THD
THD
THD
THD
THD
2
PTH12040 Single Series | Application Note 193
for Various Values of V
71.5kΩ 107kΩ 165kΩ 287kΩ 649kΩ
30.1kΩ 43.2kΩ 63.4kΩ 97.6kΩ 169kΩ
25.5kΩ 36.5kΩ 51.1kΩ 73.2kΩ 110kΩ
23.2kΩ 30.9kΩ 42.2kΩ 57.6kΩ 82.5kΩ
18.2kΩ 24.3kΩ 31.6kΩ 41.2kΩ 54.9kΩ 73.2kΩ
16.2kΩ 21.5kΩ
12.7kΩ 16.5kΩ
20kΩ
15kΩ
14kΩ
10
0.5V
3
9
1
PTH12060W
27.4kΩ 36.5kΩ 48.7kΩ 64.9kΩ 90.9kΩ
19.6kΩ 25.5kΩ 32.4kΩ 41.2kΩ 52.3kΩ
18.2kΩ 23.2kΩ
in
0.6V
with respect to GND. Figure 9 shows the
7
8
28kΩ
21kΩ
0.7V
R
set
HYS
5
4
36.5kΩ 46.4kΩ 60.4kΩ
26.1kΩ 32.4kΩ 40.2kΩ
28kΩ
and V
0.8V
HYS
6
V
o
Sense
and R
THD
36.5kΩ 45.3kΩ
+
0.9V
C
330µF
THD
out
GND
V
out
(Default)
402kΩ
187kΩ
124kΩ
N/A
1V
L
O
A
D