lm613i-mdc National Semiconductor Corporation, lm613i-mdc Datasheet - Page 18

• Manufacturer Part Number: lm613i-mdc
• Description: Dual Operational Amplifiers, Dual Comparators, And Adjustable Reference
• Manufacturer: National Semiconductor Corporation

www.national.com
Typical Performance Distributions
Application Information
VOLTAGE REFERENCE
Reference Biasing
The voltage reference is of a shunt regulator topology that
models as a simple zener diode. With current I
“forward” direction there is the familiar diode transfer func-
tion. I
voltage to be developed from cathode to anode. The cath-
ode may swing from a diode drop below V
voltage or to the avalanche voltage of the parallel protection
diode, nominally 7V. A 6.3V reference with V
lowed.
r
flowing in the reverse direction forces the reference
Voltage Reference Broad-Band
Commercial Temperature Range
Noise Distribution
Average I
OS
Drift
−
to the reference
r
+
flowing in the
00922626
= 3V is al-
00922625
(Continued)
18
The reference equivalent circuit reveals how V
constant 1.2V by feedback, and how the FEEDBACK pin
passes little current.
To generate the required reverse current, typically a resistor
is connected from a supply voltage higher than the reference
voltage. Varying that voltage, and so varying I
effect with the equivalent series resistance of less than an
ohm at the higher currents. Alternatively, an active current
source, such as the LM134 series, may generate I
FIGURE 1. Voltage Associated with Reference
FIGURE 2. Reference Equivalent Circuit
(current source I
Noise Distribution
Op Amp Current
r
is external)
00922630
00922629
r
00922628
is held at the
r
, has small
r
.