Datasheet

V
OVL
= [(R1 + R2) x ((1.16V) - 20 PA)] + 1.16V
R3
R2 =
1.17V x R1
(V
UVL
- 1.17V)
- R3
R3 =
1.16V x R1 x V
UVL
V
OVH
x (V
UVL
- 1.17V)
R1 =
V
UVH
- V
UVL
20 PA
UVLO
OVLO
R1
4
3
V
IN
LM25069
TP1
14k
R3
1.47k
R2
3.48k
UVLO/OVLO Input Voltage Thresholds www.ti.com
Figure 5. UVLO, OVLO Inputs (Option A)
To change the thresholds in this configuration, resistors R1-R3 are calculated using the following
procedure:
• 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:
(7)
(8)
(9)
The lower OVLO threshold is calculated from:
(10)
8.2 Option B
If all four thresholds must be determined accurately, move the jumper at JMP1 to pins 1-2, and add R4,
resulting in the configuration shown in Figure 6.
6
AN-1947 LM25069 Evaluation Board SNVA388D–February 2009–Revised May 2013
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