TSA7887

Page 8

TSA7887 Rev. 1.0

TSA7887 CONTROL REGISTER DESCRIPTION

The TSA7887’s write-only control register is 8-bits

wide. Serial ADC configuration data is uploaded

from the host processor at the TSA7887’s DIN pin

on low-to-high SCLK transitions. Serial input data is

uploaded to the TSA7887 simultaneously as the

conversion result is transferred out of the TSA7887.

All serial data transfers require 16 serial clocks

serial data available on the first eight low-to-high

SCLK transitions is transferred into the control

register. The first bit in the serial data stream is

always interpreted as the MSB. Upon initial power-

up, the TSA7887’s default control register bit is

cleared to all zeros (all “0”s). Table 1 lists the

functions of the Control Register’s 8 bits.

Table 1. TSA7887’s 8-Bit Control Register Content Description

DB7 (MSB)

DB6

DB5

DB4

DB3

DB2

DB1

DB0 (LSB)

DONTC

ZERO

REF

SIN/DUAL

CH

ZERO

PM1

PM0

DBx

Label

Comment

7

DONTC

Control Register DB7: Bit status of DB7 is “Don’t Care.” In other words, the DB7 bit can be a “0” or a “1”.

6

ZERO

Control Register DB6: To ensure correct TS7887 operation, Control Register DB6 status must always be a “zero”

(“0”).

5

REF

Control Register DB5 – Internal Voltage Reference Configuration: The status of DB5 determines whether the

TSA7887’s internal voltage reference is enabled or disabled. A “0” in the DB5 location will enable the TSA7887’s

internal voltage reference (default condition). To disable the TSA7887’s internal voltage reference, a “1” must be

written into DB5’s register location.

4

SIN/DUAL

Control Register DB4 - Single-Channel/Dual-Channel Configuration. Control Register DB4 configures the TSA7887 as

a single-channel or two-channel ADC. Loading a “zero” (“0”) into this register location configures the TSA7887 for

single-channel operation with the AIN1/VREF pin configured to for internal VREF operation (default configuration). In

this case, the analog input signal range is 0V to VREF. Loading a “one” (“1”) into this register location configures the

TSA7887 for two-channel operation with the AIN1/VREF pin configured to its AIN1 function as the second analog

input. In addition, the conversion process’s reference voltage is internally connected to VDD. In this case, the analog

input signal range is 0V to VDD. To obtain best performance from the TSA7887 in two-channel operation, the ADC’s

internal reference should be disabled; that is, a “1” should be loaded into DB5’s register location.

3

CH

Control Register DB3 - Channel Select Bit: The bit status of DB3 determines on which channel the TSA7887 is

converting. When the ADC is configured for dual-channel operation, DB3 determines which channel is converted on

the next conversion cycle. When DB3 is a “zero” (a “0”), the AIN0 input is selected and, when DB3 is a “one” (a “1”),

the AIN1 input is selected. DB3 should be a “zero” (“0”) when the TSA7887 is configured for single-channel operation.

2

ZERO

Control Register DB2: To ensure correct TS7887 operation, Control Register DB2 status must always be a “zero”

(“0”).

1

PM1

Control Register DB1 and DB0 - Power Management Operating Modes: DB1 and DB0 are decoded to configure the

TSA7887 into one of four operating modes as shown in Table 2.

0

PM0

Table 2. TSA7887’s Power Management Operating Modes

PM1

PM0

Mode

0

0

PM Mode 1: In this operating mode, the TSA7887’s power-down mode is enabled if its CS input is a “one” ( a “1”) and is

operating in full-power mode when its CS input is a “zero” (a “0”). Thus, the TSA7887 is powered down on a low-to-high

CS transition and is powered up on a high-to-low CS transition.

0

1

PM Mode 2: In this operating mode and regardless of the status of any of the logic inputs, the TSA7887 is always fully

powered up.

1

0

PM Mode 3: In this operating mode, the TSA7887 is automatically powered down at the end of each conversion

regardless of the state of the CS input. ADC wake-up time from full shutdown is 5

μs and system design should ensure

that at least 5

μs have elapsed before attempting to perform a conversion in this mode; otherwise, an invalid conversion

result may occur.

1

1

PM Mode 4: In this operating mode, the TSA7887 is configured for standby operation after conversion. Sections of the

TSA7887 are powered down; however, the internal 2.5-V reference voltage remains powered up. While PM Mode 4 is

similar to PM Mode 3, PM Mode 4 operation allows the TSA7887 to power up much faster. For optimal performance, the

Control Register’s REF bit (DB5) should be a “zero” (“0”) to ensure the internal reference is enabled/remains enabled.