Datasheet

LT6656
12
6656fa
0 2 4 6
MINUTES
8
0
75
150
225
300
6656 F10
10
120s
40s
t
P
30s
T
P
= 260°C
RAMP
DOWN
RAMP TO
150°C
T
S
= 190°C
T = 150°C
t
L
130s
T
L
= 217°C
T
S(MAX)
= 200°C
380s
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.
To reduce the effects of stress-related shifts, position
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. See Application Note AN82 for more
information. http://www.linear.com
The input and output capacitors should be mounted close
to the package. The GND and V
OUT
traces should be as
short as possible to minimize the voltage drops caused
by load and ground currents. Excessive trace resistance
directly impacts load regulation.
Figure 10. Lead Free Reflow Profile Due to IR Reflow
Figure 11. Output Voltage Shift Due to IR Reflow,
Peak Temperature = 260°C
CHANGE IN OUTPUT VOLTAGE (ppm)
0 6020
NUMBER OF UNITS
7
6
4
2
1
5
3
0
6656 F11
220180140100
3 CYCLES
1 CYCLE
2.5V OPTION
V
IN
= 3V
C
L
= 1µF
I
L
= 0
IR reflow. Common lead free IR reflow profiles reach over
250°C, considerably more than lead solder profiles. The
higher reflow temperature of the lead free parts exacerbates
the issue of thermal expansion and contraction causing
the output shift to generally be greater than with a leaded
reflow process.
The lead free IR reflow profile used to experimentally
measure the output voltage shift in the LT6656-2.5 is
shown in Figure 10. Similar results can be expected using
a convection reflow oven. Figure 11 shows the change
in output voltage that was measured for parts that were
run through the reflow process for 1 cycle and also 3
cycles. The results indicate that the standard deviation
of the output voltage increases with a positive mean shift
of 120ppm. While there can be up to 220ppm of output
voltage shift, additional drift of the LT6656 after IR reflow
does not vary significantly.
Figure 9. –40°C to 85°C Hysteresis
HYSTERESIS (ppm)
–160 –120 –40–80
NUMBER OF UNITS
20
18
14
12
8
4
16
10
6
2
0
6656 F09
16012040 800
–40°C TO 25°C
85°C TO 25°C
2.5V OPTION
V
IN
= 3V
C
L
= 1µF
I
L
= 0
Figure 8. 0°C to 70°C Hysteresis
HYSTERESIS (ppm)
–60 –40 –20
NUMBER OF UNITS
30
25
15
5
20
10
0
6656 F08
6040200
2.5V OPTION
V
IN
= 3V
C
L
= 1µF
I
L
= 0
0°C TO 25°C
70°C TO 25°C