LM4935RLEVAL datasheet(43/91 Pages) TI1

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SDI

CLK

Ignored

Address

SAR Data

GPIO2

TEST_MODE/CS

SDI

CLK

SAR Data

GPIO2

TEST_MODE/CS

LM4935, LM4935RLEVAL

www.ti.com

SNAS296D – OCTOBER 2005 – REVISED MARCH 2006

The full scale digital output from the SAR is equal to 2.5V. The A_VDD and D_VDD inputs are divided by

two during sampling. The SAR ADC can be activated at any time, even while the chip is in shutdown

mode (chip mode '00'). This allows the LM4935 to perform housekeeping duties such as voltage

monitoring with minimal power consumption.

*Depending on SLOT_2_VBB in SAR_SLOT23 (0x1Ch).

Only the 8 MSBS [11:4] from the 12 bits of SAR output data can be read back using the I2C interface.

The SPI interface can be used to access all 12 bits of the SAR output data. In this case, GPIO2 should be

set to SAR_SDO by setting GPIO_SEL in register (0x1Ah). The SAR channel selected by SAR_CH_SEL

in the GPIO register is then output onto GPIO2 as follows:

Figure 4-17. SPI SAR Read Transaction (GPIO2 set to SAR_SDO)

In applications where the 8 MSBS [11:4] from the SAR output data is enough resolution, GPIO2 should be

set to SPI_SDO by setting GPIO_SEL in register (0x1Ah). The SAR data is then output on GPIO2 as

follows:

Figure 4-18. SPI SAR Read Transaction (GPIO2 set to SPI_SDO)

If the user performs a write to the GPIO register the changes will not take effect until the next SPI

operation so SAR data can be read while the next channel is being selected. The SAR data is sampled at

the start of the SPI transaction to ensure that the data is stable during the read operation.

All 12 bits of the SAR output data for up to 2 SAR channels can be read back simultaneously through the

bi-directional I2S interface. This is accomplished by setting I2S_SDO_DATA (bit [7:6] of (0x19h)) to the

desired SAR channel(s).

As mentioned previously in the Section 4.2.32 section, when SAR SDO is passed to the I2S bus, the SAR

SDO's MSB is aligned with the MSB of I2S_SDO.

Application Information

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LM4935RLEVAL Datasheet(PDF) 43 Page - Texas Instruments