LT1790AIS6-3.3#PBF Linear Technology, LT1790AIS6-3.3#PBF Datasheet - Page 22

• Manufacturer Part Number: LT1790AIS6-3.3#PBF
• Manufacturer: Linear Technology

Specifications of LT1790AIS6-3.3#PBF

• Fixed / Adjust / Prog: Precision
• Output Voltage (max): 3.3V
• Temperature Coefficient: 10ppm/°C
• Reference Voltage Accuracy (max): 0.05
• Line Regulation: 170ppm/V
• Load Regulation: 160ppm/mA
• Input Voltage (max): 20V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 6
• Package Type: TSOT-23
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
LT1790
the shift after 1 cycle, while Figure 12 shows shift after
3 cycles. In the worst case, shifts are typically 150ppm,
but may be as high as 290ppm. Shifts in output voltage
are proportional to temperature and dwell time.
In general, the output shift can be reduced or fully recov-
ered by a long (12-24 hour) bake of the completed PC
Board assembly at high temperature (100°C to 150C°)
after soldering to remove mechanical stress that has been
induced by thermal shock. Once the PC Boards have cooled
to room temperature, they may continue to shift for up to
3 times the bake time. This should be taken into account
before any calibration is performed.
Higher Input Voltage
The circuit in Figure 13 shows an easy way to increase the
input voltage range of the LT1790. The Zener diode can be
anywhere from 6V to 18V. For equal power sharing between
R1 and the Zener (at 30V), the 18V option is better. The
circuit can tolerate much higher voltages for short periods
and is suitable for transient protection.
22
BZX84C18
Figure 12. 3X IR Refl ow Peak Temperature = 250°C,
3.0
1.5
3.5
2.5
2.0
1.0
0.5
0
Figure 13. Extended Supply Range Reference
4V TO 30V
70
90
R1
Delta Output Voltage (ppm)
0.1μF
110
C1
130
150
170
PPM
LT1790-3.3
190
210
230
250
1μF
270
1790 F12
290
1790 F13
V
OUT
Assuming 80μA max supply current for the LT1790, a
25μA load, 120mV max dropout and a 4V to 30V input
specifi cation, the largest that R1 can be is (4V – 3.3V
– 120mV)/(80μA + 25μA) = 5.5k. Furthermore, assum-
ing 220mW of dissipation in the 18V SOT-23 Zener, this
gives a max current of (220mW)/(18V) = 12.2mA. So the
smallest that R1 should be is (30V – 18V)/12.2mA = 1k,
rated at 150mW.
With R1 = 1k, and assuming a 450mV worst-case drop-
out, the LT1790 can deliver a minimum current of (4V
– 3.3V–450mV)/(1k) = 250μA. In Figure 13, R1 and C1
provide fi ltering of the Zener noise when the Zener is in
its noisy V-I knee.
There are other variations for higher voltage operation that
use a pass transistor shown in Figures 14 and 15. These
circuits allow the input voltage to be as high as 160V while
maintaining low supply current.
BZX84C12
Figure 15. Extended Supply Range Reference
Figure 14. Extended Supply Range Reference
330k
R1
MMBT5551
ON SEMI
0.1μF
4.7k
R2
LT1790
C1
330k
R1
LT1790
0.1μF
BAV99
C2
1μF
C1
1790 F15
ON SEMI
MMBT5551
V
OUT
V
6.5V TO 160V
S
V
6V TO 160V
S
1790 F14
C2
1μF
V
OUT
1790fb