PRODUCT SPECIFICATION FAN1582
REV. 1.1.3 11/9/03 7
The current out of the adjust pin adds to the current from R1
and is typically 50µA. Its output voltage contribution is
small and only needs consideration when a very precise out-
put voltage setting is required.
Figure 2. Basic Regulator Circuit
Load Regulation
The FAN1582 family provides true remote sensing, eliminat-
ing output voltage errors due to trace resistance. To utilize
remote sensing, connect the VSENSE pin directly to the
load, rather than at the VOUT pin. If the load is more than 1"
away from the FAN1582, it may be necessary to increase the
load capacitance to ensure stability.
Thermal Considerations
The FAN1582 series protect themselves under overload con-
ditions with internal power and thermal limiting circuitry.
However, for normal continuous load conditions, do not exceed
maximum junction temperature ratings. It is important to
consider all sources of thermal resistance from junction-to-
ambient. These sources include the junction-to-case resistance,
the case-to-heat sink interface resistance, and the heat sink
resistance. Thermal resistance specifications have been
developed to more accurately reflect device temperature and
ensure safe operating temperatures. The electrical character-
istics section provides a separate thermal resistance and
maximum junction temperature for both the control circuitry
and the power transistor. Calculate the maximum junction
temperature for both sections to ensure that both thermal
limits are met.
For example, look at using an FAN1582M-1.5 to generate
3A @ 1.5V ± 2% from a 3.3V source (3.2V to 3.6V).
Assumptions:
•V
in
= 3.6V worst case
•V
OUT
= 1.47V worst case
•I
OUT
= 3A continuous
•T
A
= 70°C
• Θ
Case-to-Ambient
= 5°C/W (assuming both a heatsink and a
thermally conductive material)
The power dissipation in this application is:
P
D
= (V
IN
- V
OUT
) * (I
OUT
) = (3.6-1.47) * (3) = 6.39W
From the specification table,
T
J
= T
A
+ (P
D
) * (Θ Case-to-Ambient + Θ
JC
)
= 70 + (6.39) * (5 + 3) = 121°C
The junction temperature is below the maximum rating.
Junction-to-case thermal resistance is specified from the IC
junction to the bottom of the case directly below the die. This
is the lowest resistance path for heat flow. Proper mounting
ensures the best thermal flow from this area of the package to
the heat sink. Use of a thermally conductive material at the
case-to-heat sink interface is recommended. Use a thermally
conductive spacer if the case of the device must be electri-
cally isolated and include its contribution to the total thermal
resistance.
C2
22µF
V
IN
V
OUT
V
REF
C1
10µF
V
cntl
+
+
Vcntl Vsense
Vin
Adj
Vout
FAN1582
R1
R2
I
ADJ
50µA
V
OUT
= V
REF
(1+R2/R1) + I
ADJ
(R2)
Figure 3. Application Circuit (FAN1582)
100µF
C2
10µF
C3
V
CNTL
= 5V
2.1V at 3A
V
IN
= 3.3V
+
10µFC1
1µF
C4
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1582
86.6Ω
124Ω
R2
R1
U1
