Datasheet

R4 =
(V
OVH
- 2.5V)
2.5V x R3
R3 =
V
OVH
- V
OVL
21 PA
=
V
OV(HYS)
21 PA
R2 =
(V
UVL
- 2.5V)
2.5V x R1
R1 =
V
UVH
- V
UVL
21 PA
=
V
UV(HYS)
21 PA
VIN
UVLO
OVLO
GND
R3
R2
R1
TIMER AND GATE
LOGIC CONTROL
LM5069
21PA
21
PA
2.5V
2.5V
V
SYS
R4
V
OVL
= [(R1 + R2) x (2.5V) - 21 PA)] + 2.5V
R3
V
OVH
=
2.5V x (R1 + R2 + R3)
R3
V
UVL
=
2.5V x (R1 + R2 + R3)
R2 + R3
V
UVH
= 2.5V + [R1 x (21 PA +
(R2 + R3)
2.5V
)]
R2 =
2.5V x 190.5 k:
(32V - 2.5V)
- 8.61 k: = 7.53 k:
LM5069
www.ti.com SNVS452D –SEPTEMBER 2006–REVISED MAY 2013
The lower OVLO threshold calculates to 55.8V, and the OVLO hysteresis is 4.2V. Note that the OVLO hysteresis
is always slightly greater than the UVLO hysteresis in this configuration. When the R1-R3 resistor values are
known, the threshold voltages and hysteresis are calculated from the following:
V
UV(HYS)
= R1 x 21 µA
V
OV(HYS)
= (R1 + R2) x 21 µA
Option B: If all four thresholds must be accurately defined, the configuration in Figure 34 can be used.
Figure 34. Programming the Four Thresholds
The four resistor values are calculated as follows:
- Choose the upper and lower UVLO thresholds (V
UVH
) and (V
UVL
).
-Choose the upper and lower OVLO threshold (V
OVH
) and (V
OVL
).
As an example, assume the application requires the following thresholds: V
UVH
= 22V, V
UVL
= 17V, V
OVH
= 60V,
and V
OVL
= 58V. Therefore V
UV(HYS)
= 5V, and V
OV(HYS)
= 2V. The resistor values are:
R1 = 238 kΩ, R2 = 41 kΩ
R3 = 95.2 kΩ, R4 = 4.14 kΩ
Where the R1-R4 resistor values are known, the threshold voltages and hysteresis are calculated from the
following:
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