ISLA112P50 Intersil, ISLA112P50 Datasheet - Page 17

• Manufacturer Part Number: ISLA112P50
• Description: 500MSPS A/D Converter
• Manufacturer: Intersil

This relationship shows the SNR that would be achieved
if clock jitter were the only non-ideal factor. In reality,
achievable SNR is limited by internal factors such as
linearity, aperture jitter and thermal noise. Internal
aperture jitter is the uncertainty in the sampling instant
shown in Figure 2. The internal aperture jitter combines
with the input clock jitter in a root-sum-square fashion,
since they are not statistically correlated, and this
determines the total jitter in the system. The total jitter,
combined with other noise sources, then determines the
achievable SNR.
Voltage Reference
A temperature compensated voltage reference provides
the reference charges used in the successive
approximation operations. The full-scale range of each
A/D is proportional to the reference voltage. The nominal
value of the voltage reference is 1.25V.
Digital Outputs
Output data is available as a parallel bus in
LVDS-compatible or CMOS modes. In either case, the
data is presented in double data rate (DDR) format.
Figures 2 and 3 show the timing relationships for LVDS
and CMOS modes, respectively.
Additionally, the drive current for LVDS mode can be set
to a nominal 3mA or a power-saving 2mA. The lower
current setting can be used in designs where the receiver
is in close physical proximity to the A/D. The applicability
of this setting is dependent upon the PCB layout,
therefore the user should experiment to determine if
performance degradation is observed.
The output mode and LVDS drive current are selected via
the OUTMODE pin as shown in Table 2.
The output mode can also be controlled through the SPI
port, which overrides the OUTMODE pin setting. Details
100
95
90
85
80
75
70
65
60
55
50
1M
OUTMODE PIN
TABLE 2. OUTMODE PIN SETTINGS
FIGURE 34. SNR vs CLOCK JITTER
AVDD
AVSS
Float
tj = 100ps
INPUT FREQUENCY (Hz)
10M
tj = 10ps
17
tj = 1ps
tj = 0.1ps
100M
LVDS, 3mA
LVDS, 2mA
LVCMOS
MODE
10 BITS
14 BITS
12 BITS
ISLA112P50
1G
on this are contained in “Serial Peripheral Interface” on
page 22.
An external resistor creates the bias for the LVDS drivers.
A 10kΩ, 1% resistor must be connected from the RLVDS
pin to OVSS.
Over Range Indicator
The over range (OR) bit is asserted when the output code
reaches positive full-scale (e.g. 0xFFF in offset binary
mode). The output code does not wrap around during an
over-range condition. The OR bit is updated at the
sample rate.
Power Dissipation
The power dissipated by the ISLA112P50 is primarily
dependent on the sample rate and the output modes:
LVDS vs. CMOS and DDR vs. SDR. There is a static bias
in the analog supply, while the remaining power
dissipation is linearly related to the sample rate. The
output supply dissipation changes to a lesser degree in
LVDS mode, but is more strongly related to the clock
frequency in CMOS mode.
Nap/Sleep
Portions of the device may be shut down to save power
during times when operation of the A/D is not required.
Two power saving modes are available: Nap, and Sleep.
Nap mode reduces power dissipation to less than
164mW and recovers to normal operation in
approximately 2.75µs. Sleep mode reduces power
dissipation to less than 6mW but requires approximately
1ms to recover from a sleep command.
Wake-up time from sleep mode is dependent on the state
of CSB; in a typical application CSB would be held high
during sleep, requiring a user to wait 150µs max after
CSB is asserted (brought low) prior to writing ‘001x’ to
SPI Register 25. The device would be fully powered up, in
normal mode 1ms after this command is written.
Wake-up from Sleep Mode Sequence (CSB high)
• Pull CSB Low
• Wait 150µs
• Write ‘001x’ to Register 25
• Wait 1ms until A/D fully powered on
In an application where CSB was kept low in sleep
mode, the 150µs CSB setup time is not required as the
SPI registers are powered on when CSB is low, the chip
power dissipation increases by ~ 15mW in this case.
The 1ms wake-up time after the write of a ‘001x’ to
register 25 still applies. It is generally recommended to
keep CSB high in sleep mode to avoid any unintentional
SPI activity on the A/D.
All digital outputs (Data, CLKOUT and OR) are placed in a
high impedance state during Nap or Sleep. The input
clock should remain running and at a fixed frequency
during Nap or Sleep, and CSB should be high. Recovery
time from Nap mode will increase if the clock is stopped,
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March 30, 2010
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