Datasheet

MAX1246/MAX1247
+2.7V, Low-Power, 4-Channel,
Serial 12-Bit ADCs in QSOP-16
______________________________________________________________________________________ 21
TMS320LC3x Interface
Figure 20 shows an application circuit to interface the
MAX1246/MAX1247 to the TMS320 in external clock
mode. The timing diagram for this interface circuit is
shown in Figure 21.
Use the following steps to initiate a conversion in the
MAX1246/MAX1247 and to read the results:
1) The TMS320 should be configured with CLKX
(transmit clock) as an active-high output clock and
CLKR (TMS320 receive clock) as an active-high
input clock. CLKX and CLKR on the TMS320 are
tied together with the MAX1246/MAX1247’s SCLK
input.
2) The MAX1246/MAX1247’s CS pin is driven low by
the TMS320’s XF_ I/O port to enable data to be
clocked into the MAX1246/MAX1247’s DIN.
3) An 8-bit word (1XXXXX11) should be written to the
MAX1246/MAX1247 to initiate a conversion and
place the device into external clock mode. Refer to
Table 1 to select the proper XXXXX bit values for
your specific application.
4) The MAX1246/MAX1247’s SSTRB output is moni-
tored via the TMS320’s FSR input. A falling edge on
the SSTRB output indicates that the conversion is in
progress and data is ready to be received from the
MAX1246/MAX1247.
5) The TMS320 reads in one data bit on each of the
next 16 rising edges of SCLK. These data bits rep-
resent the 12-bit conversion result followed by four
trailing bits, which should be ignored.
6) Pull CS high to disable the MAX1246/MAX1247 until
the next conversion is initiated.
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
100 . . . 001
100 . . . 000
- FS
COM*
INPUT VOLTAGE (LSB)
OUTPUT CODE
ZS = COM
+FS - 1LSB
*COM VREF / 2
+ COM
FS
=
VREF
2
-FS = + COM
-VREF
2
1LSB =
VREF
4096
≤
Figure 17. Bipolar Transfer Function, Full Scale (FS) =
VREF / 2 + COM, Zero Scale (ZS) = COM
+3V
+3V
GND
SUPPLIES
DGND+3VDGNDCOM
AGNDV
DD
DIGITAL
CIRCUITRY
MAX1246
MAX1247
R* = 10Ω
*OPTIONAL
Figure 18. Power-Supply Grounding Connection