LTC2402 datasheet(11/32 Pages) LINER

11 / 32 page

LTC2401/LTC2402

integrity of the conversion result and of the serial interface

mode selection which is performed at the initial power-up.

(See the 2-wire I/O sections in the Serial Interface Timing

Modes section.)

When the VCC voltage rises above this critical threshold,

the converter creates an internal power-on-reset (POR)

signal with duration of approximately 0.5ms. The POR

signal clears all internal registers. Following the POR

signal, the LTC2401/LTC2402 start a normal conversion

cycle and follows the normal succession of states de-

scribed above. The first conversion result following POR

is accurate within the specifications of the device.

Reference Voltage Range

The LTC2401/LTC2402 can accept a reference voltage

(VREF = FSSET – ZSSET) from 0V to VCC. The converter

output noise is determined by the thermal noise of the

front-end circuits, and as such, its value in microvolts is

nearly constant with reference voltage. A decrease in

reference voltage will not significantly improve the

converter’s effective resolution. On the other hand, a

reduced reference voltage will improve the overall con-

verter INL performance. The recommended range for the

LTC2401/LTC2402 voltage reference is 100mV to VCC.

Input Voltage Range

The converter is able to accommodate system level

offset and gain errors as well as system level overrange

situations due to its extended input range, see Figure 2.

The LTC2401/LTC2402 convert input signals within the

extended input range of – 0.125 • VREF to 1.125 • VREF

(VREF = FSSET – ZSSET).

For large values of VREF (VREF = FSSET – ZSSET), this range

is limited by the absolute maximum voltage range of

– 0.3V to (VCC + 0.3V). Beyond this range, the input ESD

protection devices begin to turn on and the errors due to

the input leakage current increase rapidly.

Input signals applied to VIN may extend below ground by

– 300mV and above VCC by 300mV. In order to limit any

fault current, a resistor of up to 5k may be added in series

with the VIN pin without affecting the performance of the

device. In the physical layout, it is important to maintain

APPLICATIO S I FOR ATIO

the parasitic capacitance of the connection between this

series resistance and the VIN pin as low as possible;

therefore, the resistor should be located as close as

practical to the VIN pin. The effect of the series resistance

on the converter accuracy can be evaluated from the

curves presented in the Analog Input/Reference Current

section. In addition, a series resistor will introduce a

temperature dependent offset error due to the input leak-

age current. A 1nA input leakage current will develop a

1ppm offset error on a 5k resistor if VREF = 5V. This error

has a very strong temperature dependency.

Output Data Format

The LTC2401/LTC2402 serial output data stream is 32 bits

long. The first 4 bits represent status information indicat-

ing the sign, selected channel, input range and conversion

state. The next 24 bits are the conversion result, MSB first.

The remaining 4 bits are sub LSBs beyond the 24-bit level

that may be included in averaging or discarded without

loss of resolution.

Bit 31 (first output bit) is the end of conversion (EOC)

indicator. This bit is available at the SDO pin during the

conversion and sleep states whenever the CS pin is LOW.

This bit is HIGH during the conversion and goes LOW when

the conversion is complete.

Bit 30 (second output bit) for the LTC2402, this bit is LOW

if the last conversion was performed on CH0 and HIGH for

CH1. This bit is always low for the LTC2401.

24012 F02

VCC + 0.3V

FSSET + 0.12VREF

FSSET

–0.3V

(VREF = FSSET – ZSSET)

ZSSET – 0.12VREF

ZSSET

NORMAL

INPUT

RANGE

EXTENDED

INPUT

RANGE

ABSOLUTE

MAXIMUM

INPUT

RANGE

Figure 2. LTC2401/LTC2402 Input Range

LTC2402 Datasheet(PDF) 11 Page - Linear Technology

LTC2402 Datasheet(HTML) 11 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Descarga

Enlace URL