Datasheet

V
OVL
= 1.16V + [R3 x (1.16V - 23 PA)]
R4
V
OVH
=
1.16V x (R3 + R4)
R4
V
UVL
=
1.16V x (R1 + R2)
R2
V
UVH
= 1.16V + [R1 x (1.16V + 23 PA)]
R2
R4 =
(V
OVH
- 1.16V)
1.16V x R3
R3 =
V
OVH
- V
OVL
23 PA
=
V
OV(HYS)
23 PA
R2 =
(V
UVL
- 1.16V)
1.16V x R1
R1 =
V
UVH
- V
UVL
23 PA
=
V
UV(HYS)
23 PA
VIN
UVLO/EN
OVLO
GND
R1
R3
R4
1.16V
1.16V
23 PA
TIMER AND
GATE
LOGIC CONTROL
LM25066I/A
V
SYS
23 PA
R2
LM25066I, LM25066IA
www.ti.com SNVS824C –JUNE 2012–REVISED MARCH 2013
Option B: If all four thresholds must be accurately defined, the configuration in Figure 42 can be used.
Figure 42. Programming the Four Thresholds
The four resistor values are calculated as follows: - Choose the upper and lower UVLO thresholds (V
UVH
) and
(V
UVL
).
(24)
(25)
- Choose the upper and lower OVLO threshold (V
OVH
) and (V
OVL
).
(26)
(27)
As an example, assume the application requires the following thresholds: V
UVH
= 8V, V
UVL
= 7V, V
OVH
= 15.5V,
and V
OVL
= 14V. Therefore V
UV(HYS)
= 1V and V
OV(HYS)
= 1.5V. The resistor values are:
R1 = 43.5 kΩ, R2 = 8.64 kΩ
R3 = 65.2 kΩ, R4 = 5.27 kΩ
When the R1-R4 resistor values are known, the threshold voltages and hysteresis are calculated from the
following:
(28)
(29)
V
UV(HYS)
= R1 x 23 µA (30)
(31)
(32)
V
OV(HYS)
= R3 x 23 µA (33)
Option C: The minimum UVLO level is obtained by connecting the UVLO/EN pin to VIN as shown in Figure 43.
Q
1
is switched on when the VIN voltage reaches the POR threshold (≊2.6V). The OVLO thresholds are set using
R3, R4. Their values are calculated using the procedure in Option B.
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