Applications information, Power-on reset, Reference-buffer compensation – Rainbow Electronics MAX1204 User Manual

Page 15: Power-down

MAX1204

5V, 8-Channel, Serial, 10-Bit ADC

with 3V Digital Interface

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__________ Applications Information

Power-On Reset

When power is first applied and if

SHDN is not pulled

low, internal power-on reset circuitry activates the
MAX1204 in internal clock mode, ready to convert with
SSTRB = high. After the power supplies are stabilized,
the internal reset time is 100µs. No conversions should
be performed during this phase. SSTRB is high on
power-up, and if

CS is low, the first logical 1 on DIN is

interpreted as a start bit. Until a conversion takes
place, DOUT shifts out zeros.

Reference-Buffer Compensation

In addition to its shutdown function,

SHDN also selects

internal or external compensation. The compensation
affects both power-up time and maximum conversion
speed. Compensated or not, the minimum clock rate is
100kHz due to droop on the sample-and-hold.

Float

SHDN to select external compensation. The

Typical

Operating Circuit

uses a 4.7µF capacitor at REF. A value

of 4.7µF or greater ensures stability and allows converter
operation at the 2MHz full clock speed. External com-
pensation increases power-up time (see the section

Choosing Power-Down Mode,

and Table 5).

Internal compensation requires no external capacitor at
REF, and is selected by pulling

SHDN high. Internal com-

pensation allows for the shortest power-up times, but is
only available using an external clock up to 400kHz.

Power-Down

Choosing Power-Down Mode

You can save power by placing the converter in a
low-current shutdown state between conversions.
Select full power-down or fast power-down mode via
bits 1 and 0 of the DIN control byte with

SHDN high or

floating (Tables 2 and 6). Pull

SHDN low at any time to

Figure 11a. External Clock Mode, 15 Clocks/Conversion Timing

Figure 11b. External Clock Mode, 16 Clocks/Conversion Timing

SCLK

DIN

DOUT

CONTROL BYTE 0

CONTROL BYTE 1

CONVERSION RESULT 0

CONVERSION RESULT 1

SSTRB

CONTROL BYTE 2

B1 B0 S1 S0