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LT1790

1790fb

APPLICATIONS INFORMATION

Figure 9. Worst-Case –40°C to 85°C Hysteresis on 80 Units

Figure 8. Worst-Case 0°C to 70°C Hysteresis on 79 Units

Hysteresis

Hysteresis data shown in Figures 8 and 9 represent the

worst-case data taken on parts from 0°C to 70°C and from

– 40°C to 85°C. Units were cycled several times over these

temperature ranges and the largest change is shown. As

expected, the parts cycled over the higher temperature

range have higher hysteresis than those cycled over the

lower range.

In addition to thermal hysteresis, the thermal shock as-

sociated with high temperature soldering may cause the

output to shift. For traditional PbSn solder temperatures,

the output shift of the LT1790 is typically just 150ppm

(0.015%).

DISTRIBUTION (ppm)

–60 –50 –40 –30 –20 –10

1790 F08

70°C TO 25°C

0°C TO 25°C

DISTRIBUTION (ppm)

–100

–80

–60

–40

–20

100

1790 F09

–40°C TO 25°C

80°C TO 25°C

For lead-free solder, IR reflow temperatures are much

higher, often 240°C to 260°C at the peak. As a result, the

packaging materials have been optimized to reduce VOUT

shift as possible during high temperature reflow. In addi-

tion, care should be taken when using lead-free solder to

minimize the peak temperature and dwell time as much

as is practical. A typical lead-free reflow profile is shown

in Figure 10. LT1790 units were heated using a similar

profile, with a peak temperature of 250°C. These parts

were run through the heating process 3 times to show the

cumulative effect of these heat cycles. Figure 11 shows

MINUTES

150

120s

40s

130s

RAMP

DOWN

130s

1790 F10

300

225

380s

TP = 260°

T = 150°C

T = 190°C

TS(MAX) = 200°C

TL = 217°C

RAMP TO

150°C

Figure 10. Lead-Free Reﬂow Proﬁle

PPM

010

1790 F11

Figure 11. 1X IR Reﬂow Peak Temperature = 250°C,

Delta Output Voltage (ppm)

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