MAX134EVKITSYS1 Maxim Integrated, MAX134EVKITSYS1 Datasheet - Page 7

• Manufacturer Part Number: MAX134EVKITSYS1
• Description: Data Conversion IC Development Tools
• Manufacturer: Maxim Integrated
• Series: MAX133, MAX134r

Batteries must be used to power the board to prevent
ground loops that can damage the board (see the
Multiple Grounds section).
There are two reasons the input voltage is limited to 40V.
First, there is a safety concern. All components on the
board are essentially at the potential connected to the
COM (J4) jack. Connecting the COM jack to an unsafe
voltage makes the entire board hazardous to touch.
Secondly, the input resistor (R6) is a size 1206 resistor
that cannot withstand large input voltages.
The MAXQ2000 was selected for its low-power require-
ment and the ability to drive the LCD display directly. The
4-digit LCD display is multiplexed 3:1. The MAXQ2000
produces the special multilevel signals required for the
display. Refer to the MAXQ2000 IC data sheet for a
detailed description of the multilevel waveforms.
The MAX134 divider stage scales AC input signals using
the same input divider as DC signals. AC signals are
then processed by an on-board AC-DC converter before
being sent to the MAX134’s analog-to-digital converter
stage.
The EV kit has an on-board AC-DC converter consisting
of two MAX9913 dual op amps performing a full-wave
conversion of AC input signals. Activating the AC mode
requires clearing the MAX134 DC bit and setting the EXT
AC bit to route the signal through the AC-DC converter.
The MAX9913’s are taken out of shutdown by clear-
ing the MAXQ2000 P2.7 bit. All three bits toggle when
the AC_ Mode button in the User_ Modes group box is
pressed.
Provisions on the board allow users to substitute an
external AC-DC converter. Cutting the PCB traces
across JU8 and JU9 removes the on-board AC-DC con-
verter. The user then connects an external converter to
the JU8 and JU9 pins attached to the MAX134.
The MAX134 reference input requires 545mV when oper-
ating in 60Hz mode, and 655mV when operating in 50Hz
mode. The on-board MAX6190 (U2) and a precision
resistor-divider (R2 and R3) provide 545mV for default
operation. A potentiometer (R4) allows the reference
voltage to be set to 655mV or any other voltage in the
MAX134’s reference-voltage range. To operate in 50Hz,
move the shunt on JU1 to the 2-3 position to select the
variable input, adjust R4 for 655mV (measured on pin 3
of JU1), and use the application program to set the 50Hz_
________________________________________________________________________________________ _ 7
MAXQ2000 Microcontroller
Maximum Input Voltage
Reference Voltage
AC Input Mode
MAX134 Evaluation Kit
Mode bit (Input Register 1, bit 0). Use the COM jack (J4)
for the ground connection when measuring the reference
voltage.
A MAX4164 quad op amp is used to generate the regu-
lated supplies and reset signal required for the various
circuit elements. The quad, low-power op amp requires
less battery drain than using separate linear regulators
for the supplies.
The digital ground level for the MAX134 and the micro-
controller circuitry is set at 5V below the battery positive
terminal. Additional voltages of 2.5V and 3.3V above the
digital ground level supply the microcontroller circuitry.
The fourth amplifier generates the reset signal that
occurs on power-up and when the Reset button located
on the top edge of the board is pressed.
In addition to these voltages, the MAX134 internally gen-
erates an analog ground approximately 3V below the
battery positive terminal. This is the analog ground that
is connected to the COM input jack.
In addition to the digital and analog grounds previously
described, there is a third ground plane on the board.
The third ground is optoisolated from the others and only
the elements associated with the USB connections are
connected to it. The optoisolators allow the USB cable to
be connected to a PC without interaction with the analog
input.
The MAX134 fixes the analog ground level at approxi-
mately 3V below the battery positive terminal. The digital
ground is set at 5V below the battery positive terminal.
Care must be taken to connect to only one of these
ground levels to avoid a ground-loop condition that
could damage the board. For normal operation, analog
ground (the COM jack connected to the circuit being
measured) must be the only external ground connection.
The safest and easiest way to monitor digital waveforms
or the MAX134 analog signals is to connect all measure-
ment equipment to the analog ground available through
the COM jack. Ensure that all inputs are earth-ground
referenced or battery powered to prevent damage. As
stated above, the on-board digital ground is approxi-
mately 2V below the analog ground level and therefore
the digital signal’s low state is approximately -2V.
Test equipment can be connected to the digital ground
(TP6) only if a battery is used as the measurement input
voltage or the evaluation board is measuring a resistor
value.
Power-Supply Circuit
Multiple Grounds