LTC2234IUK Linear Technology, LTC2234IUK Datasheet - Page 19

• Manufacturer Part Number: LTC2234IUK
• Description: IC ADC 10BIT 135MSPS SAMPL 48QFN
• Manufacturer: Linear Technology

Specifications of LTC2234IUK

• Number Of Bits: 10
• Sampling Rate (per Second): 135M
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 680mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-WFQFN, Exposed Pad
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
Overflow Bit
The converter is either overranged or underranged when
OF outputs a logic high.
Output Clock
The ADC has a delayed version of the ENC
as a digital output, CLOCKOUT. The CLOCKOUT pin can be
used to synchronize the converter data to the digital sys-
tem. This is necessary when using a sinusoidal encode. Data
will be updated just after CLOCKOUT rises and can be
latched on the falling edge of CLOCKOUT.
Output Driver Power
Separate output power and ground pins allow the output
drivers to be isolated from the analog circuitry. The power
supply for the digital output buffers, OV
to the same power supply as for the logic being driven. For
example if the converter is driving a DSP powered by a 1.8V
supply then OV
OV
can be powered with any voltage from GND up to 1V and
must be less than OV
tween OGND and OV
Output Enable
The outputs may be disabled with the output enable pin, OE.
OE high disables all data outputs including OF and
CLOCKOUT. The data access and bus relinquish times are
too slow to allow the outputs to be enabled and disabled
during full speed operation. The output Hi-Z state is intended
for use during long periods of inactivity.
Sleep and Nap Modes
The converter may be placed in shutdown or nap modes
to conserve power. Connecting SHDN to GND results in
normal operation. Connecting SHDN to V
results in sleep mode, which powers down all circuitry
including the reference and typically dissipates 1mW. When
exiting sleep mode it will take milliseconds for the output
data to become valid because the reference capacitors have
to recharge and stabilize. Connecting SHDN to V
DD
can be powered with any voltage up to 3.6V. OGND
DD
should be tied to that same 1.8V supply.
U
DD
DD
.
. The logic outputs will swing be-
U
W
DD
DD
+
, should be tied
input available
and OE to V
U
DD
and OE
DD
to GND results in nap mode, which typically dissipates
35mW. In nap mode, the on-chip reference circuit is kept
on, so that recovery from nap mode is faster than that from
sleep mode, typically taking 100 clock cycles. In both sleep
and nap mode all digital outputs are disabled and enter the
Hi-Z state.
GROUNDING AND BYPASSING
The LTC2234 requires a printed circuit board with a clean
unbroken ground plane. A multilayer board with an inter-
nal 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 signal alongside an
analog signal or underneath the ADC.
High quality ceramic bypass capacitors should be used at
the V
as shown in the block diagram on the front page of this data
sheet. Bypass capacitors must be located as close to the
pins as possible. Of particular importance are the capaci-
tors between REFHA and REFLB and between REFHB and
REFLA. These capacitors should be as close to the device
as possible (1.5mm or less). Size 0402 ceramic capacitors
are recommended. The 2.2µF capacitor between REFHA and
REFLA can be somewhat further away. The traces connect-
ing the pins and bypass capacitors must be kept short and
should be made as wide as possible.
The LTC2234 differential inputs should run parallel and
close to each other. The input traces should be as short as
possible to minimize capacitance and to minimize noise
pickup.
HEAT TRANSFER
Most of the heat generated by the LTC2234 is transferred
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 should
be soldered to a large grounded pad on the PC board. It is
critical that all ground pins are connected to a ground plane
of sufficient area.
DD
, OV
DD
, V
CM
, REFHA, REFHB, REFLA and REFLB pins
LTC2234
19
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