Datasheet
V
OUT
RT/SD
FB
VIN
SW
RTN
BST
L1
C2
R
FB2
R
FB1
R
T
C4
C3
15V - 75V
Input
LM5006
R3
C1
GND
VCC
V
IN
GND
UV
R
UV2
R
UV1
UVO
R
UVO
UV
STATUS
LG
Q1
3.01 k:
1 k:
261 k:
150 PH
100 k:
10V
1 PF
1.4:
10 PF
Si2328
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)]
R
UV1
=
R
UV2
x 2.5V
V
UVL
- 2.5V
R
UV2
=
V
UVH
- V
UVL
5PA
V
UV(HYS)
5PA
=
LM5006
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SNVS646B –FEBRUARY 2011–REVISED MARCH 2013
UV and UVO pins: The Under Voltage Detector function is used to monitor a system voltage, such as the input
voltage at VIN, by connecting the UV pin to two resistors (R
UV1
, R
UV2
) as shown in the Block Diagram. When the
voltage at the UV pin increases above its threshold the UVO pin switches low. The UVO pin is high when the
voltage at the UV input pin is below its threshold. Hysteresis is provided by the internal 5µA current source which
is enabled when the voltage at the UV pin is below its threshold. The resistor values are calculated using the
following procedure:
Choose the upper and lower thresholds (V
UVH
and V
UVL
) at V
IN
.
(13)
(14)
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:
(15)
R
UV2
= 200kΩ, R
UV1
= 43.5kΩ (16)
Capacitor C6 is added to filter noise and ripple, which may be present on the V
IN
line (see Figure 35). Where the
resistor values are known, the threshold voltages and hysteresis are calculated from the following:
(17)
(18)
V
UV(HYS)
= R
UV2
x 5 µA (19)
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 35. The circuit was tested, and the resulting performance is shown in
Figure 37 and Figure 36.
Figure 35. LM5006 Example Circuit
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