|AD1555||24-Bit - ADC with Low Noise PGA|
|AD1555 Datasheet PDF : 24 Pages |
4, 20, 21
AD1555 PIN FUNCTION DESCRIPTIONS
Programmable Gain Amplifier Output. The output of the on-chip programmable gain amplifier is
available at this pin. Refer to Table III for PGA gain settings selection.
Positive Analog Supply Voltage. +5 V nominal.
Negative Analog Supply Voltage. –5 V nominal.
Mux Input. Noninverting signal to the PGA mux input. Refer to Table III for input selection.
Mux Input. Inverting signal to the PGA mux input. Refer to Table III for input selection.
Mux Input. Noninverting test signal to the PGA mux input. Refer to Table III for input selection.
Mux Input. Inverting test signal to the PGA mux input. Refer to Table III for input selection.
Pin for Factory Use Only. This pin must be kept not connected for normal operation.
Modulator Control. These input pins control the mux selection, the PGA gain settings, and the
standby modes of the AD1555. When used with the AD1556, these pins are generally directly tied
to the CB0–CB4 output pins of the AD1556. CB0–CB2 are generally used to set the PGA gain or
cause it to enter in the PGA standby mode (refer to Table III). CB3 and CB4 select the mux input
voltage applied to the PGA as described in Table III.
Modulator Error. Digital output that is pulsed high if an overrange condition occurs in the modulator.
Modulator Output. The bitstream generated by the modulator is output in a return-to-zero data
format. The data is valid for approximately one-half a MCLK cycle. Refer to Figure 3.
Clock Input. The clock input signal, nominally 256 kHz, provides the necessary clock for the Σ-∆
modulator. When this input is static, AD1555 is in the power-down mode.
Positive Digital Supply Voltage. 5 V Nominal.
Analog Ground. Used as the ground reference for the REFIN pin.
DAC Reference Filter. The reference input is internally divided and available at this pin to provide
the reference for the ⌺-⌬ modulator. Connect an external 22 µF (5 V min) tantalum capacitor from
REFCAP1 to AGND3 to filter the external reference noise.
Reference Filter. The reference input is internally divided and available at this pin.
Reference Input. This input accepts a 3 V level that is internally divided to provide the reference for
the Σ-∆ modulator.
Modulator Input. Analog input to the modulator. Normally, this input is directly tied to
1, 21, 27, 28,
11, 22, 44
12, 23, 24, 34
AD1556 PIN FUNCTION DESCRIPTIONS
PGA and MUX Control Inputs. Sets the logic level of CB0-CB4 output pins respectively and the
state of the corresponding bit in the configuration register upon RESET or when in hardware mode.
Refer to Table III.
Output Rate Control Inputs. Sets the digital filter decimation rate and the state of the correspond-
ing bit in the configuration register upon RESET or when in hardware mode. Refer to the Filter
Specifications and Table VI.
Hardware/Software Mode Select. Determines how the device operation is controlled. In hardware
mode, H/S is high, the state of hardware pins set the mode of operation. When H/S is low, a write
sequence to the Configuration Register or a previous write sequence sets the device operation.
Positive Digital Supply Voltage. 3.3 V or 5 V nominal.
Serial Data Clock. Synchronizes data transfer to either write data on the DIN input pin or read
data on the DOUT output pin.
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