LT8708
41
Rev 0
2. Connect a resistor divider between V
IN
, FBIN, VIN-
HIMON and GND to configure the V
IN
regulation and
overvoltage thresholds (see Figure 13). Connect a
resistor divider between V
OUT,
VOUTLOMON, FBOUT
and GND to configure the V
OUT
regulation and under-
voltage thresholds (see Figure 14).
Use the following equations to calculate the resistor values:
R
IN3
=
1.207 • V
IN
V
OVIN
+
•I
FBDIV
R
IN1
=
V
OVIN
+
•R
IN3
•
1
1.207
–
1
V
IN
⎛
⎝
⎜
⎜⎜
⎞
⎠
⎟
⎟⎟
R
IN2
=
(V
OVIN
+
– V
IN
)
V
IN
•R
IN3
R
IN4
=
[(R
IN1
+
R
IN2
)•I
HYSMON
+
V
OVIN
+
– V
OVIN
–
]• 1.207
V
OVIN
+
•I
HYSMON
⎛
⎝
⎜
⎜
⎜⎜
⎞
⎠
⎟
⎟
⎟⎟
–
V
HYSMON
I
HYSMON
⎛
⎝
⎜
⎜⎜
⎞
⎠
⎟
⎟⎟
–
(V
OVIN
+
– 1.207)•R
IN3
V
OVIN
+
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
R
OUT3
=
1.207
I
FBDIV
R
OUT1
=
V
OUT•
R
OUT3
•
1
1.207
–
1
V
UVOUT
–
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
R
OUT2
=
(V
OUT
– V
UVOUT
–
)
V
UVOUT
–
•R
OUT3
R
OUT4
=
(R
OUT1
•I
HYSMON
+
V
UVOUT
+
– V
UVOUT
–
) •1.207
V
UVOUT
–
•I
HYSMON
⎛
⎝
⎜
⎜
⎜⎜
⎞
⎠
⎟
⎟
⎟⎟
–
V
HYSMON
I
HYSMON
⎛
⎝
⎜
⎜⎜
⎞
⎠
⎟
⎟⎟
–
(V
UVOUT
–
– 1.207)•R
OUT3
V
UVOUT
–
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
where:
I
FBDIV
is the desired current through the resistor string.
50μA – 100μA is a good value.
V
IN
and V
OUT
are the desired regulation voltages.
APPLICATIONS INFORMATION
Figure 12.
Figure 13. Single Divider for VINHIMON and FBIN
R
IN4
FBIN
VINHIMON
LT8708
8708 F13
V
IN
R
IN1
R
IN2
R
IN3
R
OUT4
VOUTLOMON
FBOUT
LT8708
8708 F14
V
OUT
R
OUT1
R
OUT2
R
OUT3
VINHIMON
LT8708
V
IN
R
HIMON1
R
HIMON3
R
HIMON2
VOUTLOMON
LT8708
8708 F12
V
OUT
R
LOMON1
R
LOMON3
R
LOMON2
(a) Resistor Divider for VINHIMON
(b) Resistor Divider for VOUTLOMON
Figure 14. Single Divider for VOUTLOMON and FBOUT
