Rainbow Electronics MAX1314 - Manual (Page 20)

MAX1304–MAX1306/MAX1308–MAX1310/MAX1312–MAX1314
8-/4-/2-Channel, 12-Bit, Simultaneous-Sampling ADCs
with ±10V, ±5V, and 0 to +5V Analog Input Ranges
20 ______________________________________________________________________________________
Data Throughput
The data throughput (f TH ) of the MAX1304–MAX1306/
MAX1308–MAX1310/MAX1312–MAX1314 is a function
of the clock speed (f
CLK ). In internal clock mode, f CLK =
15MHz (typ). In external clock mode, 100kHz ≤ f CLK ≤
20MHz. When reading during conversion (Figures 7 and
8), calculate f
TH as follows:
where N is the number of active channels and t
QUIET
is
the period of bus inactivity before the rising edge of
CONVST. See the Starting a Conversion section for
more information.
Table 1 uses the above equation and shows the total
throughput as a function of the number of channels
selected for conversion.
Clock Modes
The MAX1304–MAX1306/MAX1308–MAX1310/MAX1312–
MAX1314 provide a 15MHz internal conversion clock.
Alternatively, an external clock can be used.
Internal Clock
Internal clock mode frees the microprocessor from the
burden of running the ADC conversion clock. For inter-
nal clock operation, connect INTCLK/EXTCLK to AV
DD
and connect CLK to DGND. Note that INTCLK/EXTCLK
is referenced to AV
DD , not DV DD .
External Clock
For external clock operation, connect INTCLK/EXTCLK
to AGND and connect an external clock source to CLK.
Note that INTCLK/EXTCLK is referenced to AV
DD
, not
DV DD . The external clock frequency can be up to
20MHz. Linearity is not guaranteed with clock frequen-
cies below 100kHz due to droop in the T/H circuits.
f
t t
x N
f
TH
ACQ QUIET
CLK
=
+ +
+ − +
1
12 3 1 1 ( )
Table 1. Throughput vs. Channels Sampled: f
CLK
= 15MHz, t
ACQ
= 100ns, t
QUIET
= 50ns
CHANNELS
SAMPLED
(N)
CLOCK CYCLES
UNTIL
LAST RESULT
CLOCK CYCLE
FOR READING
LAST CONVERSION
TOTAL
CONVERSION
TIME (ns)
TOTAL
THROUGHPUT
(ksps)
THROUGHPUT
PER CHANNEL
(f TH )
1 12 1 800 983 983
2 15 1 1000 1643 821
3 18 1 1200 2117 705
4 21 1 1400 2474 618
5 24 1 1600 2752 550
6 27 1 1800 2975 495
7 30 1 2000 3157 451
8 33 1 2200 3310 413