MAX1407 Datasheet, PDF (42/48 Pages) Maxim Integrated Products – Low-Power, 16-Bit Multichannel DAS with Internal Reference,10-Bit DACs, and RTC

Low-Power, 16-Bit Multichannel DAS with
Internal Reference,10-Bit DACs, and RTC
V+
LX
SHDN ^MAX640
VOUT
100µH
D1
V_DD (+3.3V)
100µF
18nF
0.1µF
0.1µF
LBI VFB GND
2R
V_BAT
E1*
33µF
CPLL AV_DD
DV_DD
MAX1407
RESET
MAX1408
IN0
MAX1409
WU1
MAX1414
R
AGND
DGND
0.1µF
V_DD
RESET
µP/µC
INPUT
V_SS
*ONE TRANSISTOR (9V), ONE J CELL (6V), OR FOUR ALKALINE CELLS
Figure 21. Power-Supply Circuit Using MAX640 Step-Down DC-DC Converter
10µF
V_BAT
E1*
18nF
0.1µF
0.1µF
0.1µF
CPLL AV_DD
MAX1407
MAX1408
MAX1409
MAX1414
DV_DD
RESET
WU1
AGND
DGND
V_DD
RESET
µP/µC
INPUT
V_SS
*ONE Li+ COIN OR TWO BUTTON CELLS
Figure 22. Power-Supply Circuit Using Direct Battery Connection
V_OUT
=
V_REF
 2NB _
 ^{1024 }

− 1_

where NB is the decimal value of the DAC’s binary
input code. Table 12 shows digital codes (offset binary)
and corresponding output voltages for Figure 18
assuming R1 = R2.
Power Supplies
Power to the MAX1407/MAX1408/MAX1409/MAX1414
family can be supplied in a number of ways. Figures 19,
20, 21, and 22 are power-supply circuits using a step-up
converter, buck-boost converter, step-down converter,
and a direct battery, respectively. Choose the correct
power-supply circuit for your specific application.
Connect the MAX1407/MAX1408/MAX1409/MAX1414
AV_DD and DV_DD power supplies together. While the
latch-up performance of the MAX1407/MAX1408/
MAX1409/MAX1414 is adequate, it is important that
power is applied to the device before the analog input
signals (IN_) to avoid latch-up. If this is not possible,
limit the current flow into any of these pins to 50mA.
Electrochemical Sensor Operation
The MAX1407/MAX1408/MAX1409/MAX1414 family inter-
face with electrochemical sensors. The 10-bit DACs with
the force/sense buffers have the flexibility to connect to
many different types of sensors. Figure 23 shows how to
interface with a two electrode potentiostat. A single DAC
is required to set the bias across the sensor relative to
ground and an external precision resistor completes the
transimpedance amplifier configuration to convert the
current generated by the sensor to a voltage to be mea-
sured by the ADC. The induced error from this source is
negligible due to FB1’s extremely low input bias current.
Internally, the ADC can differentially measure directly
across the external transimpedance resistor, R_F, eliminat-
ing any errors due to voltages drifting over time, tempera-
ture, or supply voltage. Figure 24 shows a two electrode
potentiostat application that is driven at the working elec-
trode and measured at the counter electrode. With this
application, the DAC connected to the working electrode
is configured in unity gain and the DAC connected to the
42 ______________________________________________________________________________________