Rainbow Electronics MAX1068 - Manual (Page 11)

Detailed Description
The MAX1067/MAX1068 low-power, multichannel, 14-
bit ADCs feature a successive-approximation ADC,
automatic power-down, integrated +4.096V reference,
and a high-speed SPI/QSPI/MICROWIRE-compatible
interface. A DSPR input and DSPX output allow the
MAX1068 to communicate with DSPs with no external
glue logic. The MAX1067/MAX1068 operate with a sin-
gle +5V analog supply and feature a separate digital
supply allowing direct interfacing with +2.7V to +5.5V
digital logic.
Figures 3 and 4 show the functional diagrams of the
MAX1067/MAX1068, and Figures 5 and 6 show the
MAX1067/MAX1068 in a typical operating circuit. The
serial interface simplifies communication with micro-
processors (µPs).
In external reference mode, the MAX1067/MAX1068
have two power modes: normal mode and shutdown
mode. Driving CS high places the MAX1067/MAX1068
in shutdown mode, reducing the supply current to
0.6µA (typ). Pull CS low to place the MAX1067/
MAX1068 in normal operating mode. The internal refer-
ence mode offers software-programmable, power-down
options as shown in Table 5.
In SPI/QSPI/MICROWIRE mode, a falling edge on CS
wakes the analog circuitry and allows SCLK to clock in
data. Acquisition and conversion are initiated by SCLK.
The conversion result is available at DOUT in unipolar
serial format. DOUT is held low until data becomes
available (MSB first) on the 8th falling edge of SCLK
when in 8-bit transfer mode, and on the 16th falling
edge when in 16-bit transfer mode. See the Operating
Modes section. Figure 8 shows the detailed SPI/QSPI/
MICROWIRE serial-interface timing diagram.
In external clock mode, the MAX1068 also interfaces
with DSPs. In DSP mode, a frame-sync pulse from the
DSP initiates a conversion that is driven by SCLK. The
MAX1068 formats a frame-sync pulse to notify the DSP
that the conversion results are available at DOUT in
MSB-first, unipolar, serial-data format. Figure 16 shows
the detailed DSP serial-interface timing diagram (see the
Operating Modes section).
Analog Input
Figure 7 illustrates the input-sampling architecture of
the ADC. The voltage applied at REF or the internal
+4.096V reference sets the full-scale input voltage.
Track/Hold (T/H)
In track mode, the analog signal is acquired on the
internal hold capacitor. In hold mode, the T/H switches
open and the capacitive digital-to-analog converter
(DAC) samples the analog input.
MAX1067/MAX1068
Multichannel, 14-Bit, 200ksps Analog-to-Digital
Converters
______________________________________________________________________________________ 11
Pin Description (continued)
PIN
MAX1067 MAX1068
NAME FUNCTION
— 13 AIN6 Analog Input 6
— 14 AIN7 Analog Input 7
— 23 DSPX
DSP Frame-Sync Transmit Output. A frame-sync pulse at DSPX notifies the DSP that the
MSB data is available at DOUT. Leave DSPX unconnected when not in DSP mode.
— 24 N.C. No Connection. Not internally connected.
DGND
1mA C LOAD = 30pF
DOUT DOUT
C LOAD = 30pF
1mA
DGND
DV DD
a) V OL TO V OH b) HIGH-Z TO V OL AND V OH TO V OL
Figure 1. Load Circuits for DOUT Enable Time and SCLK-to-
DOUT Delay Time
DGND
1mA C LOAD = 30pF
DOUT DOUT
C LOAD = 30pF
1mA
DGND
DV DD
a) V OH TO HIGH-Z b) V OL TO HIGH-Z
Figure 2. Load Circuits for DOUT Disable Time