LTC6360CDD#PBF Linear Technology, LTC6360CDD#PBF Datasheet - Page 16

• Manufacturer Part Number: LTC6360CDD#PBF
• Manufacturer: Linear Technology

Specifications of LTC6360CDD#PBF

• Lead Free Status / Rohs Status: Supplier Unconfirmed

LTC6360
applicaTions inForMaTion
caused by the switching of the ADC sampling capacitor.
This momentarily disturbs the output of the amplifier as
charge is transferred between amplifier and ADC. The
amplifier must recover and settle from this load transient
before the acquisition period ends. An RC network at
the output of the LTC6360 helps decouple the sampling
transient of the ADC from the amplifier, reducing the
demands on the amplifier’s output stage (see Figure 9).
transients that discharge the RC filter capacitor.
The filter capacitor serves to provide the bulk of the charge
during the sampling process, while the filter resistor
dampens and attenuates any charge injected by the ADC.
The RC filter has the additional benefit of band limiting
broadband output noise.
The selection of the RC time constant depends on the ap-
plication; but generally, longer time constants will improve
SNR at the expense of longer settling time. Excessive
settling time can introduce gain errors and distortion
if the filter components are not perfectly linear. 16-bit
applications typically require a minimum settling time of
16
The resistor at the input of the ADC minimizes the sampling
0V TO 4V
V
IN
+
–
Figure 9. Driving an ADC
+IN
–IN
–
+
LTC6360
SHDN
OUT
10
5V
330pF
R ADC
CPI
V CC
CHARGE
PUMP
0.1µF
CPO
0.1µF
V
DD
ADC
GND
5V
6360 F09
5V
1µF
10µF
eleven RC time constants of a first order filter. Note also
that too small a resistor will not properly dampen the load
transient of the sampling process, prolonging the time
required for settling.
High quality resistors and capacitors should be used for
the RC filter network since these components stabilize
the internal amplifier and can also contribute their own
distortion. For lowest distortion, choose capacitors with
a high quality dielectric, such as a C0G multilayer ceramic
capacitor. Metal film surface mount resistors are more
linear than carbon types.
SHDN
The SHDN pin is 5V TTL or 3.6V CMOS level compatible.
If the SHDN pin (Pin 7) is pulled low, below 0.8V, the
LTC6360 will power down. If the pin is left open or pulled
high, above 2.0V, the part will enter normal active opera-
tion. The turn-on time between the shutdown and active
states is typically 1μs, and turn-off time is typically 0.3µs.
In shutdown, the output pin (OUT) appears as an open
collector with a nonlinear capacitor to ground and steer-
ing diodes to V
capacitance, the output will still have the ability to sink and
source small amounts of transient current if exposed to
significant voltage transients. The input protection diodes
between +IN and –IN can still conduct if voltage transients
at the input exceed 700mV.
Noise Considerations
The LTC6360 has a low noise density e
This is equivalent to the voltage noise of a 320Ω resistor
at the +IN input. For source resistors larger than 320Ω,
voltage noise due to the source resistance will start to
dominate. The current noise density is 3pA/√Hz, thus
source resistors larger than about 770Ω will interact with
the input current noise and result in output noise that is
amplifier current noise dominant.
Note that the parallel combination of gain setting resis-
tors R
noise calculations.
F
and R
G
CC
behaves like the source resistance, R
and ground. Because of the nonlinear
n
of 2.3nV/√Hz.
S
6360f
, in