X60250 Datasheet, PDF (14/16 Pages) Intersil Corporation – Micro Power Programmable Voltage Reference

X60250
TYPICAL PERFORMANCE CHARACTERISTIC CURVES (Continued)
Power On Settling Time
APPLICATIONS INFORMATION
Standard Reference configurations
Figure 8 shows the device connections to produce a 0
to 1.250V adjustable reference with 8 bits of resolution.
V_REFL will be grounded in this case. Figure 9 has
device connections to produce a 0.625V to 1.250V
reference with 8 bits of resolution, with R₁ grounded.
This configuration effectively doubles the output voltage
control resolution, increasing the accuracy of the
desired reference output voltage. Since the auxiliary
resistor is matched to the DCP resistor, temperature
drift is minimized.
Figure 8. Standard Configuration
V_REFOUT
1.25V
Reference
100K
V_OUT
R₁
Adjusted
Reference
Voltage
0.0 to 1.25V Range
100K
GND
V_REFL
Figure 9. Using Auxilliary Resistor
V_REFOUT
1.25V
Reference
100K
V_OUT
R₁
0.625V to 1.25V
Range
GND
100K
V_REFL
Reducing Output Noise
The output noise voltage of the reference is typically
200µV rms in the 10kHz bandwidth. An advantage of the
adjustable reference configuration is the ease in filtering
this noise. Simply adding a capacitor to the V_OUT pin will
produce a single pole filter with a corner frequency of:
F_CORNER
=
1_--
2
×
π
×
R_D
C
P
×
C_F
I
LTER
R_DCP will vary with tap position and wiper resistance. If
the approximate tap position of the DCP is known, it can
be used to calculate this resistance as follows:
R_DCP
=
2_----5_---5_{-----–----}t_---a_---p_----#w_{--- ×}
255
R_T
O
T
A
L
||


t_---a_---p_----w_---#_×
255
R_T
O

T A L
+ R_WIPER
For example, with V_CC = 5V, tap # = 127 (corresponding
to V_OUT = 0.623V), C_FILTER = 0.1µF, using typical values:
R_DCP = 25K + 0.6K = 25.6kΩ
F_CORNER = 62Hz
14
FN8146.1
September 14, 2005