MAX1270 Maxim, MAX1270 Datasheet - Page 9

• Manufacturer Part Number: MAX1270
• Description: Multirange / +5V / 8-Channel / Serial 12-Bit ADCs
• Manufacturer: Maxim

The ADC’s input small-signal bandwidth depends on
the selected input range and varies from 1.5MHz to
5MHz (see Electrical Characteristics). The MAX1270/
MAX1271 maximum sampling rate is 110ksps. By using
undersampling techniques, it is possible to digitize
high-speed transient events and measure periodic sig-
nals with bandwidths exceeding the ADC’s sampling
rate.
To avoid high-frequency signals being aliased into the
frequency band of interest, anti-aliasing filtering is rec-
ommended.
The MAX1270/MAX1271 have software-selectable input
ranges. Each analog input channel can be indepen-
dently programmed to one of four ranges by setting the
appropriate control bits (RNG, BIP) in the control byte
(Table 1). The MAX1270 has selectable input ranges
extending to ±10V (±V
has selectable input ranges extending to ±V
4 shows the equivalent input circuit.
A resistor network on each analog input provides
±16.5V fault protection for all channels. Whether or not
the channel is on, this circuit limits the current going
into or out of the pin to less than 2mA. This provides an
added layer of protection when momentary overvolt-
ages occur at the selected input channel, when a neg-
ative signal is applied to the input, and when the device
is configured for unipolar mode. The overvoltage pro-
tection is active even if the device is in power-down
mode or if V
Figure 5. Detailed Serial-Interface Timing
DOUT
SCLK
DIN
CS
DD
= 0.
t
CSH
____________________________________________________________________________________
Input Range and Protection
REF
t
DV
t
CSS
t
· 2.441), while the MAX1271
DS
t
DH
Input Bandwidth
t
CL
REF
. Figure
t
CH
Multirange, +5V, 8-Channel,
• • •
• • •
• • •
• • •
Figure 4. Equivalent Input Circuit
The MAX1270/MAX1271 feature a serial interface that is
fully compatible with SPI/QSPI and MICROWIRE
devices. For SPI/QSPI, set CPOL = 0, CPHA = 0 in the
SPI control registers of the microcontroller. Figure 5
shows detailed serial interface timing information. Refer
to Table 1 for programming the input control byte.
CH_
S1 = BIPOLAR/UNIPOLAR SWITCH
S2 = INPUT MUX SWITCH
S3, S4 = T/H SWITCH
R1
Serial 12-Bit ADCs
R3
5.12k
t
DO
S1
S2
R2
HOLD
UNIPOLAR
OFF
ON
BIPOLAR
t
CSH
R1 =
R2 =
S3
12.5kΩ (MAX1270)
or 5.12kΩ (MAX1271)
8.67kΩ (MAX1270)
or ∞ (MAX1271)
TRACK
Digital Interface
C
HOLD
t
TR
TRACK
S4
VOLTAGE
REFERENCE
T/H
OUT
7-177
HOLD