Datasheet

LM613
SNOSC11B –AUGUST 2000–REVISED MARCH 2013 www.ti.com
Capacitors in parallel with the reference are allowed. See the Reference AC Stability Range typical curve for
capacitance values—from 20 μA to 3 mA any capacitor value is stable. With the reference's wide stability range
with resistive and capacitive loads, a wide range of RC filter values will perform noise filtering.
Adjustable Reference
The FEEDBACK pin allows the reference output voltage, V
ro
, to vary from 1.24V to 6.3V. The reference attempts
to hold V
r
at 1.24V. If V
r
is above 1.24V, the reference will conduct current from Cathode to Anode; FEEDBACK
current always remains low. If FEEDBACK is connected to Anode, then V
ro
= V
r
= 1.24V. For higher voltages
FEEDBACK is held at a constant voltage above Anode—say 3.76V for V
ro
= 5V. Connecting a resistor across the
constant V
r
generates a current I=R1/V
r
flowing from Cathode into FEEDBACK node. A Thevenin equivalent
3.76V is generated from FEEDBACK to Anode with R2=3.76/I. Keep I greater than one thousand times larger
than FEEDBACK bias current for <0.1% error—I≥32 μA for the military grade over the military temperature range
(I≥5.5 μA for a 1% untrimmed error for a commercial part).
Figure 69. Thevenin Equivalent of Reference
with 5V Output
R1 = Vr/I = 1.24/32μ = 39k
R2 = R1 {(Vro/Vr) − 1} = 39k {(5/1.24) − 1)} = 118k
Figure 70. Resistors R1 and R2 Program Reference Output Voltage to be 5V
Understanding that V
r
is fixed and that voltage sources, resistors, and capacitors may be tied to the FEEDBACK
pin, a range of V
r
temperature coefficients may be synthesized.
20 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated
Product Folder Links: LM613