Datasheet

LM614
www.ti.com SNOSC21C –MAY 1998–REVISED MARCH 2013
Capacitors in parallel with the reference are allowed. See 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 5.0V. 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=V
r
/R1 flowing from Cathode into FEEDBACK node. A Thevenin equivalent
3.76V is generated from FEEDBACK to Anode with R2=3.76/I. For a 1% error, use R1 such that I is greater than
one hundred times the FEEDBACK bias current. For example, keep I ≥ 5.5μA.
Figure 51. 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 52. 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.
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