Datasheet

V
OVL
= [(R1 + R2) x ((2.5V) - 22 PA)] + 2.5V
R3
R1 =
V
UVH
- V
UVL
22 PA
=
V
UV(HYS)
22 PA
R3 =
2.5V x R1 x V
UVL
V
OVH
x (V
UVL
- 2.5V)
R2 =
2.5V x R1
V
UVL
- 2.5V
- R3
OVLO
VEE
TIMER AND GATE
LOGIC CONTROL
GND
VEE
To Load
Vee
R2
LM5067
22 PA
C
IN
R
IN
V
SYS
R1
R3
UVLO/EN
22 PA
Vee
Vee
2.50V
2.50V
VCC
LM5067
SNVS532C –OCTOBER 2007–REVISED MARCH 2013 www.ti.com
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 LM5067 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.
NOTE
All voltages are with respect to Vee in the discussions below. Use absolute values in the
equations.
Option A: The configuration shown in Figure 14 requires three resistors (R1-R3) to set the thresholds.
Figure 14. UVLO and OVLO Thresholds Set By R1-R3
The procedure to calculate the resistor values is as follows:
• Determine the upper UVLO threshold (V
UVH
) to enable Q1, and the lower UVLO threshold (V
UVL
) to disable
Q1.
• Determine the upper OVLO threshold (V
OVH
) to disable Q1.
• The lower OVLO threshold (V
OVL
), to enable Q1, 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:
(10)
The lower OVLO threshold is calculated from:
(11)
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