Datasheet

R3 =
2.5V x 190.5 k: x 32V
60V x (32V - 2.5V)
= 8.61 k:
R1 =
36V ± 32V
21 PA
=
4V
21 PA
= 190.5 k:
V
OVL
= [(R1 + R2) x ((2.5V) - 21 PA)] + 2.5V
R3
R2 =
2.5V x R1
V
UVL
- 2.5V
- R3
R3 =
2.5V x R1 x V
UVL
V
OVH
x (V
UVL
- 2.5V)
R1 =
V
UVH
- V
UVL
21 PA
=
V
UV(HYS)
21 PA
VIN
UVLO
OVLO
GND
R1
R2
R3
TIMER AND GATE
LOGIC CONTROL
LM5069
21PA
21
PA
2.50V
2.50V
V
SYS
t
RESTART
= C
T
x
7 x 2.75V
2.5 PA
7 x 2.75V
85 PA
3.7V
2.5 PA
++
LM5069
SNVS452D –SEPTEMBER 2006–REVISED MAY 2013 www.ti.com
= C
T
x 9.4 x 10
6
For example, if C
T
= 0.33 µF, t
RESTART
= 3.1 seconds. At the end of the restart time, Q1 is switched on. If the fault
is still present, the fault timeout and restart sequence repeats. The on-time duty cycle of Q1 is approximately
0.5% in this mode.
UVLO, OVLO
By programming the UVLO and OVLO thresholds the LM5069 enables the series pass device (Q1) when the
input supply voltage (V
SYS
) is within the desired operational range. If V
SYS
is below the UVLO threshold, or above
the OVLO threshold, Q1 is switched off, denying power to the load. Hysteresis is provided for each threshold.
Option A: The configuration shown in Figure 33 requires three resistors (R1-R3) to set the thresholds.
Figure 33. UVLO and OVLO Thresholds Set By R1-R3
The procedure to calculate the resistor values is as follows:
- Choose the upper UVLO threshold (V
UVH
), and the lower UVLO threshold (V
UVL
).
- Choose the upper OVLO threshold (V
OVH
).
- The lower OVLO threshold (V
OVL
) cannot be chosen in advance in this case, but is determined after the
values for R1-R3 are determined. If V
OVL
must be accurately defined in addition to the other three thresholds, see
Option B below.
The resistors are calculated as follows:
The lower OVLO threshold is calculated from:
As an example, assume the application requires the following thresholds: V
UVH
= 36V, V
UVL
= 32V, V
OVH
= 60V.
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