LT6656 Linear Technology Corporation, LT6656 Datasheet - Page 7

• Manufacturer Part Number: LT6656
• Description: 1?a Precision Series Voltage Reference
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
Long Battery Life
Series references have a large advantage over shunt style
references. Shunt references require a resistor from the
power supply to operate. This resistor must be chosen
to supply the maximum current that can be demanded by
the load. When the load is not operating at this maximum
current, the shunt reference must always sink this current,
resulting in high dissipation and shortened battery life.
The LT6656 series reference does not require a current
setting resistor and is specified to operate with any sup-
ply from V
current and operating temperature (see Dropout Voltage
in the Typical Performance Characteristics). When the
load does not demand current, the LT6656 reduces its
dissipation and battery life is extended. If the reference
is not delivering load current, it dissipates only a few µW,
yet the same connection can deliver 5mA of load current
when required.
Start-Up
To ensure proper start-up, the output voltage should be
between –0.3V and 2.5V. If the output load may be driven
more than 0.3V below ground, a low forward voltage
schottky diode from the output to ground is required. The
turn-on characteristics can be seen in Figure 1.
Bypass and Load Capacitance
The LT6656 voltage reference needs an input bypass
capacitor of 0.1µF or larger, however, the bypassing of
other local devices may serve as the required component.
1V/DIV
V
OUT
V
IN
Figure 1. Turn-On Characteristics, C
OUT
+ 10mV to 18V, depending on the load
1ms/DIV
L
= 1µF
6656 F01
The output of the device requires a capacitance of 1µF or
larger. With its low sensitivity to ESR, the LT6656 is stable
with a wide variety of capacitor types including ceramic,
tantalum and electrolytic. The test circuit in Figure 2 was
used to test the response and stability of the LT6656 to
various load currents. The resultant transient responses
can be seen in Figure 3 and Figure 4. The large scale out-
put response to a 500mV input step is shown in Figure 5
with a more detailed photo and description in the Output
Settling section.
V
0.1µF
3V
IN
V
V
C
I
I
OUT
OUT
OUT
OUT
IN
Figure 3. Transient Response, 0µA to 100µA Load Step
(R2 = 24.9k, R1 = Open)
Figure 4. Transient Response, 1mA to 2mA Load Step
(R1 = R2 = 2.49k)
100µA
2.52V
2.50V
2.48V
2.52V
2.50V
2.48V
1mA
2mA
0µA
4
Figure 2. Transient Load Test Circuit
LT6656-2.5
1, 2
6
5ms/DIV
5ms/DIV
C
1µF
L
R1
R2
2N7000
6656 F03
6656 F04
LT6656
V
GEN
6656 F02

6656f
3V