LTC6652AHMS8-1.25-PBF LINER [Linear Technology], LTC6652AHMS8-1.25-PBF Datasheet - Page 14

• Manufacturer Part Number: LTC6652AHMS8-1.25-PBF
• Description: Precision Low Drift Low Noise Buffered Reference
• Manufacturer: LINER [Linear Technology]

LTC6652
PC Board Layout
The mechanical stress of soldering a surface mount volt-
age reference to a PC board can cause the output voltage
to shift and temperature coefficient to change. These two
changes are not correlated. For example, the voltage may
shift, but the temperature coefficient may not.
To reduce the effects of stress-related shifts, mount the
reference near the short edge of the PC board or in a
corner. In addition, slots can be cut into the board on two
sides of the device.
The capacitors should be mounted close to the package.
The GND and V
to minimize I • R drops. Excessive trace resistance directly
impacts load regulation.
IR Reflow Shift
The different expansion and contraction rates of the materi-
als that make up the lead-free LTC6652 package cause the
output voltage to shift after undergoing IR reflow. Lead-free
reflow profiles reach over 250°C, considerably more than
their leaded counterparts. The lead-free IR reflow profile
used to experimentally measure output voltage shift in the
LTC6652-2.5 is shown in Figure 14. Similar results can be
14
applications inForMation
225
150
300
75
0
0
Figure 14. Lead-Free Reflow Profile
RAMP TO
150°C
T = 150°C
OUT
T
S
= 190°C
T
2
traces should be as short as possible
S(MAX)
= 200°C
4
380s
MINUTES
120s
T
L
= 217°C
T
P
6
= 260°C
130s
40s
30s
t
t
P
L
8
DOWN
RAMP
6652 F14
10
expected using a convection reflow oven. In our experiment,
the serialized parts were run through the reflow process
twice. The results indicate that the standard deviation of
the output voltage increases with a slight positive mean
shift of 0.003% as shown in Figure 15. While there can
be up to 0.016% of output voltage shift, the overall drift
of the LTC6652 after IR reflow does not vary significantly.
Power Dissipation
Power dissipation in the LTC6652 is dependent on V
load current, and package. The LTC6652 package has
a thermal resistance, or θ
illustrates allowed power dissipation vs temperature for
this package is shown in Figure 16.
The power dissipation of the LTC6652-2.5V as a function
of input voltage is shown in Figure 17. The top curve
shows power dissipation with a 5mA load and the bottom
curve shows power dissipation with no load.
When operated within its specified limits of V
and sourcing 5mA, the LTC6652-2.5 consumes just under
60mW at room temperature. At 125°C the quiescent cur-
rent will be slightly higher and the power consumption
increases to just over 60mW. The power-derating curve
in Figure 16 shows the LTC6652-2.5 can safely dissipate
125mW at 125°C about half the maximum power con-
sumption of the package.
Humidity Sensitivity
Plastic mould compounds absorb water. With changes
in relative humidity, plastic packaging materials change
the amount of pressure they apply to the die inside,
which can cause slight changes in the output of a volt-
age reference, usually on the order of 100ppm. The LS8
package is hermetic, so it is not affected by humidity, and
is therefore more stable in environments where humidity
may be a concern.
JA
, of 200°C/W. A curve that
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