The MAX186 digital signals are available on the 8-pin

header located on the bottom edge of the board. This

header provides convenient connections for scope

probes or a ribbon cable.

Conversion Cycles

The MAX186 performs conversions on demand or at

preset intervals. The conversion sequence does not

vary with the two methods. If the device is in shutdown

mode, a dummy conversion brings it out of shutdown,

and the program delays to allow the reference voltage

to settle. Then, as many as eight conversions are per-

formed to collect data for a complete line of the screen

display. Finally, if shutdown mode is enabled, another

dummy conversion returns the MAX186 to the proper

shutdown state.

Shutdown Mode

The MAX186 has two shutdown levels. The FULL shut-

down mode completely disables the MAX186 reference

circuit and reduces supply current to 2µA. A delay of

300µs is required to activate from this shutdown state.

The delay must be greater when the external reference

compensation capacitor, C6, is installed. Be sure to set

the reference settling delay whenever the FULL shut-

down mode is used. Table 5 of the MAX186/MAX188

data sheet lists the reference settling times required for

different external capacitors.

The second shutdown level disables only the reference

output buffer. This drops the supply current to 30µA,

but requires a shorter delay (5µs with internal compen-

sation) between activation and conversion cycles. This

is referred to as the FAST shutdown mode.

is programmed high so that it always enables the

MAX186 in normal operation. All modes are controlled

through software. In FAST or FULL shutdown mode, the

MAX186 is placed in shutdown between conversion

cycles and activated just before the conversions begin.

This reduces the average supply current but will

require a delay before the conversions. The

MAX186EVKIT Personal Computer Program section has

information on varying the delay and controlling the

shutdown mode.

abling the internal compensation of the reference

buffer. The external compensation capacitor, C6, is

supplied with the kit but not mounted on the PCB. If you

wish to use external compensation, cut the trace across

JU2 and mount the 22µF capacitor, C6. The reference

settling delay must be increased. See the MAX186/

MAX188 data sheet for descriptions of internal and

external reference compensation.

Evaluating External

Reference Voltages

The MAX186 can be operated with an external refer-

ence voltage if the internal reference is disabled.

internal reference. Soldering a short piece of wire

across jumper JU3 will make this connection. The 22µF

capacitor should also be soldered into location C6

when using an external voltage. The reference voltage

is then applied to the pad labeled VREF.

To use the MAX188, which requires an external refer-

ence, install C6 and connect the reference source to

the VREF pad.

Jumper JU1 facilitates monitoring the MAX186 supply

current in the shutdown modes. The jumper allows the

insertion of a current meter in series with the MAX186

cuit trace between the two holes marked JU1. Then sol-

der two short leads in each hole and connect the amme-

ter. A short piece of wire can be soldered across the

jumper location to restore normal connections.

Analog Inputs

Each of the eight inputs has a 300

Ω resistor in series.

These optional resistors were included as current-limiting

devices for input overvoltage conditions. There is also an

optional 0.01µF capacitor on each of the inputs. This pro-

vides the low source impedance required when the

channel is the low side of a differential input pair. The

input capacitors are not required on channels used as

single-ended inputs. Refer to the Pseudo-Differential

Input section of the data sheet.

MAX186 Evaluation System/Evaluation Kit

4

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