tc3400 Microchip Technology Inc., tc3400 Datasheet - Page 6

• Manufacturer Part Number: tc3400
• Description: +1.8v, Low Power, 16-bit Sigma-delta A/d Converter
• Manufacturer: Microchip Technology Inc.

TC3400
3.0
The TC3400 is a 16-bit sigma-delta A/D converter with
one differential input. See the Typical Application circuit
and the Functional Block diagram. The key components
of the TC3400 are described below.
Also refer to Figure 3-4, A/D Operational Flowchart and
the Timing Diagrams, Figure 3-1, Figure 3-2 and
Figure 3-3).
3.1
When the TC3400 is not converting, it is in sleep mode
with both the SCLK and SDAT lines high. An A/D
conversion is initiated by a high to low transition on the
SCLK line at which time the internal clock of the
TC3400 is started. Each additional high to low
transition of SCLK (following the initial SCLK falling
edge) during the time interval t
conversion resolution by one bit and reduce the
conversion time by one half. The time interval t
referred to as the resolution reduction window. The
minimum conversion resolution is 10-bits so any more
than 6 SCLK transitions during t
After each high to low transition of SCLK, in the t
interval, the SDAT output is driven high by the TC3400
to acknowledge that the conversion has been decre-
mented. When the SCLK returns high or the t
ends, the SDAT line returns low (see Figure 3-2). When
the conversion is complete SDAT is driven high. The
TC3400 now enters sleep mode and the conversion
value can be read as a serial data word on the SDAT
line.
3.2
After the conversion is complete and SDAT goes high,
the conversion value can be clocked serially onto the
SDAT line by high to low transitions of the SCLK. The
data word is in two’s compliment format with the sign bit
clocked onto the SDAT line, first followed by the MSB
and ending in the LSB. For a 16-bit conversion the data
word would consist of a sign bit followed by 15 magni-
tude bits, Table 3-1 shows the data word versus input
voltage for a 16-bit conversion. Note that the full scale
input voltage range is ±(2 REF
REF
for a 16-bit conversion, as REF
Figure 3-3 shows typical SCLK and SDAT waveforms
for 16, 12 and 10-bit conversions. Note that any
complete convert and read cycle requires 17 negative
edge clock pulses. The first is the convert command.
Then, up to six of these can occur in the resolution
reduction window, t
remaining pulses clock out the conversion data word.
DS21409B-page 6
OUT
DETAILED DESCRIPTION
A/D Converter Operation
Reading the Data Word
is fed back directly to REF
4
, to decrement resolution. The
OUT
4
4
, will decrement the
will be ignored.
IN
IN
is typically 1.193V.
, an LSB is 73µV
– 1LSB). When
4
interval
4
is
4
TABLE 3-1:
The SCLK input has a filter which rejects any positive
or negative pulse of width less than 50nsec to reduce
noise. The rejection width of this pulse can vary
between 50nsec and 750nsec depending on process-
ing parameters and supply voltage.
Figure 3-1 and Table 3-2 show information for deter-
mining the mode of operation for the TC3400 part by
recording the value of SDAT for SCLK in a high, then
low, then high state. For example, if SCLK goes
through a 1-0-1 transition and the corresponding val-
ues of SDAT are 1-1-0, then the SCLK falling edge
started a new data conversion. A 0-1-0 for SDAT would
have indicated a resolution reduction had occurred.
This is useful if the microcontroller has a watchdog
reset or otherwise loses track of where the TC3400 is
in the conversion and data readout sequence. The
microcontroller can simply transition SCLK until it
“finds” a Start Conversion condition.
FIGURE 3-1:
TABLE 3-2:
*
Note: The code X00 has a dual meaning: Data Transfer or
0111 1111 1111 1111
0000 0000 0000 0001
0000 0000 0000 0000
1111 1111 1111 1111
1000 0000 0000 0001
1000 0000 0000 0000
SDAT
SCLK
A
1
0
x
x
Busy converting. To avoid confusion, the user should
send only the required number of pulses for the
desired resolution, then wait for SDAT to rise to 1,
indicating conversion is complete before clocking
SCLK again to read out data bits.
Data Word
B
1
1
1
0
A
C
0
0
1
0
DATA CONVERSION WORD
VS. VOLTAGE INPUT
(REF
SCLK, SDAT LOGIC STATE
Start Conversion
Resolution Reduction
Data Transfer
Data Transfer or Busy*
STATE DIAGRAM
SCLK, SDAT LOGIC
©
IN
2002 Microchip Technology Inc.
= 1.193V)
2.38596 (Positive Full Scale)
72.8 E -6
0
-72.8 E -6
-2.38596 (Negative Full Scale)
Reserved Code
B
INn+ – INn- (Volts)
Status
C