ltc2258cuj-12 Linear Technology Corporation, ltc2258cuj-12 Datasheet - Page 27

• Manufacturer Part Number: ltc2258cuj-12
• Description: 12-bit, 65/40/2 5msps Ultralow Power 1.8v Adcs
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
GROUNDING AND BYPASSING
The LTC2258-12 requires a printed circuit board with a
clean unbroken ground plane. A multilayer board with
an internal ground plane is recommended. Layout for
the printed circuit board should ensure that digital and
analog signal lines are separated as much as possible. In
particular, care should be taken not to run any digital track
alongside an analog signal track or underneath the ADC.
High quality ceramic bypass capacitors should be used at
the V
capacitors must be located as close to the pins as possible.
Of particular importance is the 0.1μF capacitor between
REFH and REFL. This capacitor should be on the same
side of the circuit board as the A/D, and as close to the
device as possible (1.5mm or less). Size 0402 ceramic
capacitors are recommended. The larger 2.2μF capacitor
between REFH and REFL can be somewhat further away.
REGISTER A4: DATA FORMAT REGISTER (ADDRESS 04h)
Bit 7-6
Bits 5-3
Bit 2
Bit 1
Bit 0
DD
D7
X
, OV
DD
, V
Unused, Don’t Care Bits.
OUTTEST2:OUTTEST0
000 = Digital Output Test Patterns Off
001 = All Digital Outputs = 0
011 = All Digital Outputs = 1
101 = Checkerboard Output Pattern. OF , D11-D0 Alternate Between 1 0101 1010 0101 and 0 1010 0101 1010
111 = Alternating Output Pattern. OF , D11-D0 Alternate Between 0 0000 0000 0000 and 1 1111 1111 1111
Note: Other Bit Combinations are not Used
ABP
0 = Alternate Bit Polarity Mode Off
1 = Alternate Bit Polarity Mode On
RAND
0 = Data Output Randomizer Mode Off
1 = Data Output Randomizer Mode On
TWOSCOMP Two’s Complement Mode Control Bit
0 = Offset Binary Data Format
1 = Two’s Complement Data Format
Note: ABP = 1 forces the output format to be Offset Binary
CM
, V
D6
X
REF
, REFH and REFL pins. Bypass
Alternate Bit Polarity Mode Control Bit
Data Output Randomizer Mode Control Bit
OUTTEST2
D5
Digital Output Test Pattern Bits
OUTTEST1
D4
The V
as possible. To make space for this the capacitor on V
can be further away or on the back of the PC board. The
traces connecting the pins and bypass capacitors must be
kept short and should be made as wide as possible.
The analog inputs, encode signals, and digital outputs
should not be routed next to each other. Ground fi ll and
grounded vias should be used as barriers to isolate these
signals from each other.
HEAT TRANSFER
Most of the heat generated by the LTC2258-12 is trans-
ferred from the die through the bottom-side exposed pad
and package leads onto the printed circuit board. For good
electrical and thermal performance, the exposed pad must
be soldered to a large grounded pad on the PC board.
OUTTEST0
D3
CM
LTC2257-12/LTC2256-12
capacitor should be located as close to the pin
ABP
D2
RAND
LTC2258-12
D1
TWOSCOMP
D0
27
225812p
REF