STLC3080 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STLC3080' PDF : 23 Pages View PDF
STLC3080
APPENDIX B
STLC3080: allowed Rfeed values vs. Ilim
The STLC3080 device has been designed in or-
der to fit in a small SMD package (TQFP44). This
target has been achieved by using a dedicated
circuit for power management based on one ex-
ternal transistor (Qext).
The particular power management circuit adopted
allows to define the percentage of power dissi-
pated on the SLIC itself and on the Qext. The
sharing percentage is defined by the Rfeed value,
in particular the higher is Rfeed, the higher is the
percentage dissipated on the SLIC.
Rfeed represents the DC feeding impedance at
TIP/RING terminals (including 2xRp) when the
SLIC is in the resistive feed region of the DC
characteristics.
Since the max. power dissipation inside the SLIC
is limited it is important to know which value of
Rfeed can be implemented without exceeding the
max power allowed in the SLIC.
In order to define the allowed Rfeed values sev-
eral other parameters should be considered, in
particular:
Pdslic:
Max allowed power dissipation on SLIC, two val-
ues are considered:
1.1W for 70°C Tamb application;
0.9W for 85°C Tamb application;
Pdqext:
Max allowed power dissipation on Qext, three val-
ues are considered:
1.0W
1.5W
2.0W
These values depend on the package and the as-
sembly of the Qext.
Ilim:
Programmed constant current value, continuous
variations are considered from 20mA to 50mA.
Vbat:
Battery voltage, three values are considered:
48V
54V
62V
The following diagrams show the allowed Rfeed
values depending on the above parameters. three
diagrams are shown each one for a particular bat-
tery (Vbat = -48V, -54V, -60V).
In each diagrams you can find an upper and a
lower limits for the Rfeed value:
The upper limit is defined by one of the two b1, b2
curves.
b1 is the limit when max. power on SLIC is
equal to 0.9W (Tamb = 85°C)
b2 is the limit when max. power on SLIC is
equal to 1.1W (Tamb = 70°C)
The lower limit is defined by one of the three a1,
a2, a3 curves.
a1 is the limit when max. power allowed on
Qext is equal to 1.0W
a2 is the limit when max. power allowed on
Qext is equal to 1.5W
a3 is the limit when max. power allowed on
Qext is equal to 2.0W
Figure B1. Rfeed allowed values vs. Ilim (Vbat = -48V).
16/23
Share Link: 
