LT1790 Linear Technology, LT1790 Datasheet - Page 6

• Manufacturer Part Number: LT1790
• Description: 2.5V Micropower SOT-23 Low Dropout Reference
• Manufacturer: Linear Technology

APPLICATIONS
LT1790-2.5
Positive or Negative Operation
Series operation is ideal for extending battery life. If the
LT1790-2.5 is operated in series mode it does not require
an external current setting resistor. The specifications
guarantee the LT1790-2.5 operates from 2.6V to 18V.
When the circuitry being regulated does not demand
current, the series connected LT1790-2.5 consumes only
a few hundred W, yet the same connection can sink or
source 5mA of load current when demanded. A typical
series connection is shown on the front page of this data
sheet.
The circuit in Figure 7 shows the connection for a – 2.5V
reference. The LT1790-2.5 can be used as a very stable
negative reference, however, it requires a positive voltage
applied to Pin 4 to bias internal circuitry. This voltage
must be current limited with R1 to keep the output PNP
6
V
GEN
8V
6V
4V
2V
0V
Figure 6. LT1790-2.5 Sinking – 4mA to – 5mA
U
INFORMATION
U
Figure 7. Using the LT1790-2.5 to Build a –2.5V Reference
W
1790 F06
R
L
=
V
6
U
V
EE
125 A
OUT
– 2.5V
LT1790-2.5
V
EE
1, 2
4
transistor from turning on and driving the grounded
output. C1 provides stability during load transients. This
connection maintains the accuracy and temperature coef-
ficient of the positive connected LT1790-2.5.
Long-Term Drift
Long-term drift cannot be extrapolated from acceler-
ated high temperature testing. This erroneous tech-
nique gives drift numbers that are widely optimistic. The
only way long-term drift can be determined is to mea-
sure it over the time interval of interest. The LT1790S6
drift data was taken on over 100 parts that were soldered
into PC boards similar to a “real world” application. The
boards were then placed into a constant temperature oven
with T
measured with an 8.5 digit DVM. Long-term drift curves
are shown in the Typical Performance Characteristics.
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.
When the LT1790-2.5 is IR reflow soldered onto a PC
board, the output shift is typically just 150ppm (0.015%).
10k
C1
0.1 F
C
1 F
R1
1790 F07
L
V
A
OUT
3V
= 30 C, their outputs scanned regularly and
= –2.5V