TSA7887
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
transitions. After a high-to-low CS transition
signal
,
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)
DONTC
DBx
7
6
DB6
ZERO
Label
DONTC
ZERO
DB5
REF
DB4
SIN/DUAL
DB3
CH
DB2
ZERO
DB1
PM1
DB0 (LSB)
PM0
Comment
Control Register DB7: Bit status of DB7 is “Don’t Care.” In other words, the DB7 bit can be a “0” or a “1”.
Control Register DB6: To ensure correct TS7887 operation, Control Register DB6 status must always be a “zero”
(“0”).
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.
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.
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.
Control Register DB2: To ensure correct TS7887 operation, Control Register DB2 status must always be a “zero”
(“0”).
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.
5
REF
4
SIN/DUAL
3
CH
2
1
0
ZERO
PM1
PM0
Table 2. TSA7887’s Power Management Operating Modes
PM1
0
PM0
0
Mode
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.
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.
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 5μs and system design should ensure
that at least 5μs have elapsed before attempting to perform a conversion in this mode; otherwise, an invalid conversion
result may occur.
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.
0
1
1
0
1
1
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TSA7887DS r1p0
RTFDS
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