US1010 UNISEM, US1010 Datasheet - Page 5

• Manufacturer Part Number: US1010
• Description: 1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR
• Manufacturer: UNISEM

Rev. 1.3
10/30/00
Thermal Design
The US1010 incorporates an internal thermal shutdown
that protects the device when the junction temperature
exceeds the maximum allowable junction temperature.
Although this device can operate with junction tempera-
tures in the range of 150 C ,it is recommended that the
selected heat sink be chosen such that during maxi-
mum continuous load operation the junction tempera-
ture is kept below this number. The example below for
a SCSI terminator application shows the steps in se-
lecting the proper regulator in a surface mount pack-
age .(See US1015 for non surface mount packages)
Assuming the following specifications :
Where ; V
as shown in figure 4.
The steps for selecting the right package with proper
board area for heatsinking to keep the junction tem-
perature below 135 C is given as :
1) Calculate the maximum power dissipation using :
2) Calculate the maximum
ample:
2) Select a package from the datasheet with lower
than the one calculated in the previous step.
Selecting TO252 (D Pak) with at least 0.5" square of
0.062" FR4 board using 1OZ copper has 70 C/W
which is lower than the calculated number.
I
V
V
V
T
P
P
OUT
JA
JA
A
IN
F
O
D
D
MAX
MAX
MAX
0 5
35
I
2 85
0 8
5
F
OUT
.
.
.
V
is the forward voltage drop of the D1diode
135
T
0 8
V
C
.
J
V
P
132
.
A
5
D
V
T
IN
A
35
0 5
.
V
F
75 6
2 85
.
.
V
OUT
JA
C W
allowed for our ex-
/
132
.
W
JA
To set the output DC voltage, we need to select R1 and
R2 :
3) Assuming R1=121
Select R2=154
Layout Consideration
The output capacitors must be located as close to
the Vout terminal of the device as possible. It is recom-
mended to use a section of a layer of the PC board as a
plane to connect the Vout pin to the output capacitors to
prevent any high frequency oscillation that may result
due to excessive trace inductance.
5V
R
2
10uF
C1
Figure 4 - Final Schematic for half of the
D1
V
V
OUT
REF
Vin
1
GTL+ termination regulator.
,1%
US1010
121
Adj
, 1%
2 85
125
.
.
Vout
1
R1
121
1%
R2
154
1%
121
US1010
1010app4-1.3
154.8
2-5
C2
22uF
2.85V