Rainbow Electronics MAX188 - Manual (Page 9)

Full Scale
V
REFADJ
x A*
Analog Input Range and Input Protection
Internal protection diodes, which clamp the analog
input to V
DD
and V
SS
, allow the channel input pins to
swing from V
SS
- 0.3V to V
DD
+ 0.3V without damage.
However, for accurate conversions near full scale, the
inputs must not exceed V
DD
by more than 50mV, or be
lower than V
SS
by 50mV.
If the analog input exceeds 50mV beyond the sup-
plies, do not forward bias the protection diodes of
off-channels over two milliamperes, as excessive
current will degrade the conversion accuracy of the
on-channel.
The full-scale input voltage depends on the voltage at
VREF. See Tables 1a and 1b.
Quick Look
To evaluate the analog performance of the
MAX186/MAX188 quickly, use the circuit of Figure 5.
The MAX186/MAX188 require a control byte to be writ-
ten to DIN before each conversion. Tying DIN to +5V
feeds in control bytes of $FF (HEX), which trigger
MAX186/MAX188
Low-Power, 8-Channel,
Serial 12-Bit ADCs
_______________________________________________________________________________________ 9
Reference
Zero
Scale
Full Scale
Internal Reference
(MAX186 only)
0V +4.096V
0V
at VREF 0V VREF
External Reference
at REFADJ
Reference
Negative
Full Scale
Zero
Scale
Internal Reference
(MAX186 only)
-4.096V/2 0V
External Reference
at REFADJ
-1/2V
REFADJ
x A*
0V
at VREF -1/2 VREF 0V
+4.096V/2
+1/2V
REFADJ
x A*
+1/2 VREF
0.1µF
V DD
DGND
AGND
V
SS
CS
SCLK
DIN
DOUT
SSTRB
SHDN
+5V
N.C.
0.01µF
CH7
REFADJ
VREF
C2
0.01µF
+2.5V
REFERENCE
C1
4.7µF
D1
1N4148
+5V
0V TO
4.096V
ANALOG
INPUT
+2.5V
**
OSCILLOSCOPE
CH1 CH2 CH3 CH4
* FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FFF (HEX)
**REQUIRED FOR MAX188 ONLY. A POTENTIOMETER MAY BE USED IN PLACE OF THE REFERENCE FOR TEST PURPOSES.
MAX186
MAX188
+5V
2MHz
OSCILLATOR
SCLK
SSTRB
DOUT*
Figure 5. Quick-Look Circuit
* A = 1.678 for the MAX186, 1.638 for the MAX188
Table 1b. Bipolar Full Scale, Zero Scale, and
Negative Full Scale
Table 1a. Unipolar Full Scale and Zero Scale
* A = 1.678 for the MAX186, 1.638 for the MAX188