X60250 Datasheet, PDF (15/16 Pages) Intersil Corporation – Micro Power Programmable Voltage Reference

X60250
Since this is a single pole rolloff, the actual noise
bandwidth is 1.57 times this, or 97Hz. This should
reduce typical output noise to about 45µV rms. Note that
if the wiper is set to the highest tap positon (tap# = 255)
to give a V_OUT of 1.25V, the resulting R_DCP = R_WIPER or
600Ω, and the filter bandwidth will now be 2.6kHz,
increasing noise significantly. If tap positions near
V_REFOUT will be used, then a series resistor R_OUT should
be added to better control noise bandwidth.
Figure 10. Reducing Output Noise
V_REFOUT
1.25V
Reference
100K
V_OUT
R₁
R_OUT
(optional)
Filtered
Reference
Voltage
C_FILTER
GND
100K
V_REFL
Higher Reference Voltages
If a reference voltage higher than 1.25V is required, then
an opamp can be added to amplify the V_OUT voltage.
There are many micropower opamps available, such as
the LMV341, which can produce an output at very close
to either supply rail. Figure 11 shows a circuit for a 0V to
5.0V adjustable reference, which has 8 bits of control.
Note that if the auxiliary resistor is connected to ground
instead of V_REFL, then the output voltage range will be
2.5V to 5.0V, but resolution will double. Total current
draw from that circuit will be 156µA (typically, with
V_OUT = 5V) including reference and opamp circuitry.
Note that due to V_CC supply variations, the output may
not span up to 5.00V which would result in missing codes
at the top end of the DCP range.
Figure 11. Increasing Reference Output Voltage
V_REFOUT
+5V
1.25V
Reference
100K
R_{1 20K}
C_FILTER
5
1₊
6
4
3
LMV341
–2
0 to
5.0V
GND
100K
V_REFL
100K
33K
15
FN8146.1
September 14, 2005