LM34923 Datasheet, PDF (17/26 Pages) National Semiconductor (TI) – EVAL evaluation board provides the design engineer with a fully

LM34923
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SNVS695A – MARCH 2011 – REVISED FEBRUARY 2013
As an example, assume the application requires the following thresholds: V_UVH = 15V and V_UVL = 14V. Therefore
V_UV(HYS) = 1V. The resistor values calculate to:
(14)
R_UV2 = 200kΩ, R_UV1 = 43.5kΩ
(15)
Capacitor C6 is added to filter noise and ripple, which may be present on the V_IN line. Where the resistor values
are known, the threshold voltages and hysteresis are calculated from the following:
V_UVH = 2.5V + [R_UV2 x (_R2.U⁵_V^V₁ + 5 PA)]
(16)
V_UVL
=
2.5V
x
(R_UV1 + R_UV2)
R_UV1
(17)
V_UV(HYS) = R_UV2 x 5 µA
(18)
The pull-up voltage for the UVO output can be any voltage under 10V. The maximum continuous current into the
UVO output pin should not exceed 5 mA.
FINAL CIRCUIT
The final circuit is shown in Figure 33. The circuit was tested, and the resulting performance is shown in
Figure 34 and Figure 35.
15V - 75V
Input
V_IN
C1
GND
1 PF
VIN
VCC
C5
0.1 PF
LM34923
R_T
261 k:
BST
SHUT
DOWN
R_UV1
43.2 k:
R_UVO
100 k:
UV
STATUS
R_UV2
200 k:
C6
1000 pF
RT/SD
UV
UVO
SW
FB
RTN
C3
1 PF
0.01 PF
C4
L1 150 PH
D1
R_FB2
3.01 k:
R_FB1
1 k:
V_OUT
10V
R3
1.4:
C2
10 PF
GND
Figure 33. LM34923 Example Circuit
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