Datasheet

V
OUT
RT/SD
FB
VIN
SW
RTN
BST
L1
C2
R
FB2
R
FB1
R
T
C4
C3
15V - 75V
Input
LM34923
R3
C1
GND
VCC
V
IN
GND
UV
R
UV2
R
UV1
UVO
R
UVO
UV
STATUS
D1
3.01 k:
1 k:
261 k:
150 PH
100 k:
10V
1 PF
1.4:
10 PF
1 PF
0.01 PF
0.1 PF
C5
200 k:
43.2 k:
1000 pF
C6
SHUT
DOWN
V
UVL
= 2.5V x
R
UV1
(R
UV1
+ R
UV2
)
V
UVH
= 2.5V + [R
UV2
x (
2.5V
R
UV1
+ 5 PA)]
LM34923
www.ti.com 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:
(16)
(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.
Figure 33. LM34923 Example Circuit
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