LT1121AIS8#PBF Linear Technology, LT1121AIS8#PBF Datasheet - Page 10

• Manufacturer Part Number: LT1121AIS8#PBF
• Description: IC REG LDO ADJ 150MA 8-SOIC
• Manufacturer: Linear Technology

Specifications of LT1121AIS8#PBF

• Regulator Topology: Positive Adjustable
• Voltage - Output: 3.75 ~ 30 V
• Voltage - Input: 4.17 ~ 30 V
• Voltage - Dropout (typical): 0.42V @ 150mA
• Number Of Regulators: 1
• Current - Output: 150mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -

APPLICATIONS INFORMATION
LT1121/LT1121-3.3/LT1121-5
taken in still air, on 3/32" FR-4 board with 1oz copper. All
NC leads were connected to the ground plane.
10
Table 1. N8 Package*
Table 2. S8 Package
Table 3. AS8 Package*
Table 4. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20ºC/W)
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm
1000 sq mm 1000 sq mm 1000 sq mm
* Device is mounted on topside. Leads are through hole and are
soldered to both sides of board.
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm
100 sq mm
* Device is mounted on topside.
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm
100 sq mm
* Pins 3, 6 and 7 are ground.
** Device is mounted on topside.
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm
100 sq mm
1000 sq mm 2500 sq mm 1000 sq mm
1000 sq mm
* Tab of device attached to topside copper.
TOPSIDE**
TOPSIDE*
TOPSIDE*
TOPSIDE
COPPER AREA
COPPER AREA
COPPER AREA
COPPER AREA
2500 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
1000 sq mm 1000 sq mm
2500 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
BACKSIDE
BACKSIDE
BACKSIDE
BACKSIDE
0
BOARD AREA
BOARD AREA
BOARD AREA
BOARD AREA
1000 sq mm
JUNCTION TO AMBIENT
JUNCTION TO AMBIENT
JUNCTION TO AMBIENT
JUNCTION TO AMBIENT
THERMAL RESISTANCE
THERMAL RESISTANCE
THERMAL RESISTANCE
THERMAL RESISTANCE
120ºC/W
120ºC/W
125ºC/W
131ºC/W
80ºC/W
80ºC/W
85ºC/W
91ºC/W
60ºC/W
60ºC/W
68ºC/W
74ºC/W
50ºC/W
50ºC/W
58ºC/W
64ºC/W
57ºC/W
60ºC/W
Calculating Junction Temperature
Example: given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
100mA, and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
Power dissipated by the device will be equal to:
where, I
so,
If we use an SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on
copper area. So the junction temperature rise above ambi-
ent will be less than or equal to:
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
Output Capacitance and Transient Performance
The LT1121 is designed to be stable with a wide range of
output capacitors. The minimum recommended value is 1μF
with an ESR of 3Ω or less. For applications where space
is very limited, capacitors as low as 0.33μF can be used if
combined with a small series resistor. Assuming that the
ESR of the capacitor is low (ceramic) the suggested series
Table 5. TO-92 Package THERMAL RESISTANCE
Package alone
Package soldered into PC board with plated through
holes only
Package soldered into PC board with 1/4 sq. inch of
copper trace per lead
Package soldered into PC board with plated through
holes in board, no extra copper trace, and a clip-on type
heat sink: Thermalloy type 2224B
Aavid type 5754
I
V
I
P = 100mA • (7V – 3.3V) + (5mA • 7V)
= 0.405W
0.405W • 60°C/W = 24°C
T
OUT MAX
OUT MAX
GND
JMAX
IN MAX
at (I
= 50°C + 24°C = 74°C
= 7V
• (V
OUT
= 100mA
IN MAX
= 100mA, V
– V
OUT
IN
) + (I
= 7V) = 5mA
GND
• V
IN
220ºC/W
175ºC/W
145ºC/W
160ºC/W
135ºC/W
)
1121ff