7
FN9100.8
December 3, 2015
Biasing the ISL6116
Table 3 gives typical component values for biasing the
ISL6116 in a ±48V application. The formulas and
calculations deriving these values are also shown in the
following equations.
When using the ISL6116 to control -48V, a Zener diode
may be used to provide the +12V bias to the chip. If a
Zener is used then a current limit resistor should also
be used. Several items must be taken into account
when choosing values for the current limit resistor
(R
CL
) and Zener Diode (DD1):
• The variation of the V
BUS
(in this case, -48V
nominal)
• The chip supply current needs for all functional
conditions
• The power rating of R
CL
.
• The current rating of DD1
Formulas
Sizing R
CL
is expressed in Equation 1:
Power Rating of R
CL
is expressed in Equation 2:
DD1 current rating is expressed in Equation 3:
Example:
A typical -48V supply may vary from -36 to -72V.
Therefore:
V
BUS,MAX
= -72V
V
BUS,MIN
= -36V
I
CHIP
= 15mA (Max)
Sizing R
CL
is expressed in Equation 4:
Power rating of R
CL
is expressed in Equation 5:
DD1 current rating is expressed in Equation 6:
TABLE 3. TYPICAL VALUES FOR A -48V HOT SWAP
APPLICATION
SYMBOL PARAMETER
R
CL
1.58k, 1W
DD1 12V Zener Diode, 50mA Reverse Current
V
BUS
LOAD
1
2
3
4
8
7
6
5
ISL6116
PWRON
NC
FIGURE 2. TYPICAL 5A LOAD CONTROL
-48V
R
CL
DD1
12V
1.58k
1W
0.01µF
0.047µF
1.47k
0.005
1%
0.001µF
2k
1%
R
CL
V
BUS MIN
12–
I
CHIP
-------------------------------------------
=
(EQ. 1)
(EQ. 2)
P
RCL
I
C
V
BUS MAX
12–=
(EQ. 3)
I
DD1
V
BUS MAX
12–
R
CL
--------------------------------------------------
=
(EQ. 4)
R
CL
V
BUS MIN
12–
I
C
------------------------------------------------
=
R
CL
36 12–
0.015
-------------------
=
R
CL
16k TypicalValue 1.58k==
(EQ. 5)
P
RCL
I
C
V
BUS MAX
12–=
P
RCL
0.01572 12–=
P
RCL
0.9W TypicalValue 1W==
(EQ. 6)
I
DD1
V
BUS MAX
12–
R
CL
--------------------------------------------------
=
I
DD1
72 12–
1.58k
------------------------
=
I
DD1
38mA TypicalValue 12Vrating, 50mA reverse current==
ISL6115, ISL6116, ISL6117, ISL6120
