MAX1282 Datasheet, PDF (16/24 Pages) Maxim Integrated Products – 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference

300ksps/400ksps, Single-Supply, 4-Channel,
Serial 12-Bit ADCs with Internal Reference
CS
SCLK
t_CSS
t_CSO
t_DS
DIN
t_CH
t_CL
t_DH
t_DOE
DOUT
t_STE
SSTRB
t_CP
#10
t_DOH
t_DOV
t_STH
t_STV
t_CSW
t_CSH
t_CS1
t_DOD
t_STD
Figure 6. Detailed Serial-Interface Timing
Using Fast Power-Down
and Reduced-Power Modes
FASTPD and REDP modes achieve the lowest power
consumption at speeds close to the maximum sampling
rate. Figure 10 shows the MAX1283’s power
consumption in FASTPD mode (PD1 = 0, PD0 = 1),
REDP mode (PD1 = 1, PD0 = 0), and, for comparison,
normal operating mode (PD1 = 1, PD0 = 1). The figure
shows power consumption using the specified power-
down mode, with the internal reference and conversion
controlled at the maximum clock speed. The clock
speed in FASTPD or REDP should be limited to 4.8MHz
for the MAX1282/MAX1283. FULLPD mode may provide
increased power savings in applications where the
MAX1282/MAX1283 are inactive for long periods of time,
but intermittent bursts of high-speed conversions are
required. Figure 11b shows FASTPD and REDP timing.
Internal and External References
The MAX1282/MAX1283 can be used with an internal
or external reference voltage. An external reference
can be connected directly at REF or at the REFADJ pin.
An internal buffer is designed to provide 2.5V at
REF for the MAX1282/MAX1283. The internally trimmed
1.22V reference is buffered with a 2.05 gain.
Internal Reference
The MAX1282/MAX1283’s full-scale range with the inter-
nal reference is 2.5V with unipolar inputs and ±1.25V
with bipolar inputs. The internal reference voltage is
adjustable by ±100mV with the circuit in Figure 12.
External Reference
The MAX1282/MAX1283’s external reference can be
placed at the input (REFADJ) or the output (REF) of the
internal reference-buffer amplifier. The REFADJ input
impedance is typically 17kΩ. At REF, the DC input
resistance is a minimum of 18kΩ. During conversion, an
external reference at REF must deliver up to 350µA DC
load current and have 10Ω or less output impedance. If
the reference has a higher output impedance or is
noisy, bypass it close to the REF pin with a 4.7µF
capacitor.
Table 5. Full Scale and Zero Scale
UNIPOLAR MODE
Full Scale
Zero Scale
V_REF + V_COM
V_COM
Positive
Full Scale
V_REF / 2
+ V_COM
BIPOLAR MODE
Zero
Scale
V_COM
Negative
Full Scale
V_REF / 2
+ V_COM
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