Detailed Description
The MAX1062 includes an input track-and-hold (T/H)
and successive-approximation register (SAR) circuitry
to convert an analog input signal to a digital 14-bit out-
put. Figure 4 shows the MAX1062 in its simplest config-
uration. The serial interface requires only three digital
lines (SCLK, CS, and DOUT) and provides an easy
interface to microprocessors (µPs).
The MAX1062 has two power modes: normal and shut-
down. Driving CS high places the MAX1062 in shut-
down, reducing the supply current to 0.1µA (typ), while
pulling CS low places the MAX1062 in normal operating
mode. Falling edges on CS initiate conversions that are
driven by SCLK. The conversion result is available at
DOUT in unipolar serial format. The serial data stream
consists of eight zeros followed by the data bits (MSB
first). Figure 3 shows the interface-timing diagram.
Analog Input
Figure 5 illustrates the input sampling architecture of
the ADC. The voltage applied at REF sets the full-scale
input voltage.
Track-and-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 DAC samples the analog
input.
During the acquisition, the analog input (AIN) charges
capacitor C
DAC
. The acquisition interval ends on the
falling edge of the sixth clock cycle (Figure 6). At this
instant, the T/H switches open. The retained charge on
C
DAC
represents a sample of the input.
In hold mode, the capacitive digital-to-analog converter
(DAC) adjusts during the remainder of the conversion
cycle to restore node ZERO to zero within the limits of
14-bit resolution. At the end of the conversion, force CS
high and then low to reset the input side of the C
DAC
switches back to AIN, and charge C
DAC
to the input
signal again.
The time required for the T/H to acquire an input signal
is a function of how quickly its input capacitance is
charged. If the input signal’s source impedance is high,
the acquisition time lengthens and more time must be
allowed between conversions. The acquisition time
(t
ACQ
) is the maximum time the device takes to acquire
the signal. Use the following formula to calculate acqui-
sition time:
t
ACQ
= 11(R
S
+ R
IN
) x 35pF
where R
IN
= 800Ω, R
S
= the input signal’s source
impedance, and t
ACQ
is never less than 1.1µs. A
source impedance less than 1kΩ does not significantly
affect the ADC’s performance.
To improve the input signal bandwidth under AC condi-
tions, drive AIN with a wideband buffer (>4MHz) that
can drive the ADC’s input capacitance and settle
quickly.
MAX1062
14-Bit, +5V, 200ksps ADC with 10µA Shutdown
_______________________________________________________________________________________ 7
Pin Description
External Reference Voltage Input. Sets the analog voltage range. Bypass to AGND with a 4.7µF
capacitor.
Analog +5V Supply Voltage. Bypass to AGND (pin 3) with a 0.1µF capacitor.
Active Low Chip Select Input. Forcing CS high places the MAX1062 in shutdown with a typical
current of 0.1µA. A high-to-low transition on CS activates normal operating mode and initiates a
conversion.
Serial Clock Input. SCLK drives the conversion process and clocks out data at data rates up to
4.8MHz.
Serial Data Output. Data changes state on SCLK’s falling edge. DOUT is high impedance when CS
is high.
Digital Supply Voltage. Bypass to DGND with a 0.1µF capacitor.
