LT6654 Datasheet, PDF (14/18 Pages) Linear Technology – SOT-23 Precision Wide Supply High Output Drive Low Noise Reference

LT6654
Applications Information
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 LT6654.
The GND and V_OUT traces should be as short as possible
to minimize I • R drops, since high trace resistance directly
impacts load regulation.
IR Reflow Shift
The different expansion and contraction rates of the ma-
terials that make up the LT6654 package may cause the
output voltage to shift after undergoing IR reflow. Lead
free solder reflow profiles reach over 250°C, considerably
more than with lead based solder. A typical lead free IR
reflow profile is shown in Figure 12. Similar profiles are
found using a convection reflow oven. LT6654 devices run
up to three times through this reflow process show that the
standard deviation of the output voltage increases with a
slight negative mean shift of 0.003% as shown in Figure 13.
While there can be up to 0.014% of output voltage shift,
the overall drift of the LT6654 after IR reflow does not
vary significantly.
300
380s
T_P = 260°C
RAMP
225
T_L = 217°C
DOWN
T_S(MAX) = 200°C
T_S = 190°C
t_P
30s
150 ^{T = 150°C}
t_L
RAMP TO
130s
150°C
40s
75
120s
0
0
2
4
6
MINUTES
8
10
6654 F12
Figure 12. Lead Free Reflow Profile
14
260°C 3 CYCLES
12 ^{260°C 1 CYCLE}
10
8
6
4
2
0
–140 –120 –100 –80 –60 –40 –20 0
CHANGE IN OUTPUT (ppm)
6654 F13
Figure 13. Output Voltage Shift Due to IR Reflow (%)
6654fb
14