LT1461AIS8-3 Linear Technology, LT1461AIS8-3 Datasheet - Page 10

• Manufacturer Part Number: LT1461AIS8-3
• Description: IC MICRPWR PREC REF LDO 3V 8SOIC
• Manufacturer: Linear Technology

Specifications of LT1461AIS8-3

• Reference Type: Series
• Voltage - Output: 3V
• Tolerance: ±0.04%
• Temperature Coefficient: 3ppm/°C
• Voltage - Input: 3.5 ~ 20 V
• Number Of Channels: 1
• Current - Quiescent: 50µA
• Current - Output: 100mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Cathode: -

APPLICATIO S I FOR ATIO
LT1461
Precision Regulator
The LT1461 will deliver 50mA with V
higher load current with higher V
typically 12ppm/mA, which means for a 50mA load step,
the output will change by only 1.5mV. Thermal regulation,
caused by die temperature gradients and created from
load current or input voltage changes, is not measurable.
This often overlooked parameter must be added to normal
line and load regulation errors. The load regulation photo,
on the first page of this data sheet, shows the output
response to 200mW of instantaneous power dissipation
and the reference shows no sign of thermal errors. The
reference has thermal shutdown and will turn off if the
junction temperature exceeds 150 C.
Shutdown
The shutdown (Pin 3 low) serves to shut off load current
when the LT1461 is used as a regulator. The LT1461
operates normally with Pin 3 open or greater than or equal
to 2.4V. In shutdown, the reference draws a maximum
supply current of 35 A. Figure 3 shows the transient
response of shutdown while the part is delivering 25mA.
After shutdown, the reference powers up in about 200 s.
10
PIN 3
V
OUT
Figure 3. Shutdown While Delivering 25mA, R
5V
0V
0V
U
U
IN
W
IN
. Load regulation is
= V
OUT
1461 F03
L
= 100
+ 2.5V and
U
PC Board Layout
In 13- to 16-bit systems where initial accuracy and tem-
perature coefficient calibrations have been done, the me-
chanical and thermal stress on a PC board (in a card cage
for instance) can shift the output voltage and mask the true
temperature coefficient of a reference. In addition, the
mechanical stress of being soldered into a PC board can
cause the output voltage to shift from its ideal value.
Surface mount voltage references are the most suscep-
tible to PC board stress because of the small amount of
plastic used to hold the lead frame.
A simple way to improve the stress-related shifts is to
mount the reference near the short edge of the PC board,
or in a corner. The board edge acts as a stress boundary,
or a region where the flexure of the board is minimum. The
package should always be mounted so that the leads
absorb the stress and not the package. The package is
generally aligned with the leads parallel to the long side of
the PC board as shown in Figure 5a.
A qualitative technique to evaluate the effect of stress on
voltage references is to solder the part into a PC board and
deform the board a fixed amount as shown in Figure 4. The
flexure #1 represents no displacement, flexure #2 is
concave movement, flexure #3 is relaxation to no dis-
placement and finally, flexure #4 is a convex movement.
This motion is repeated for a number of cycles and the
1
2
3
4
Figure 4. Flexure Numbers
1461 F04