isl55210 Intersil Corporation, isl55210 Datasheet - Page 13

• Manufacturer Part Number: isl55210
• Description: Wideband, Low-power, Ultra-high Dynamic Range Differential Amplifier
• Manufacturer: Intersil Corporation

3.6V
asymmetrically clipped maximum swing. Going 10% above this
3.7V target to 4.1V will be within the recommended operating
range and give some tolerancing headroom that would also
suggest the V
coincides with the default output V
at +4.1V single supply in a Figure 28 type configuration will give
the maximum linear available output swing of 3.6V
The differential inputs of the ISL55210 also have operating
range limits relative to the supply voltages. Operating in an AC
coupled circuit like Figure 28 will produce an input common
mode voltage equal to the outputs. The inputs can operate with
full linearity with this V
connection (or -V
+3.3V supplies this gives a 100mV guardband on the input V
voltages. Overriding the default V
to the V
negative supply due to this limit. On the + side, the maximum
V
the output V
When operated as a DC coupled single to differential amplifier,
the input common mode voltage will move with the input signal
and will be different than the output common mode voltage
when the external resistors are set for gain. When the input
common mode can be different than the output, the additional
constraint that must be observed is that the input common mode
voltage cannot be > output V
the single source was coming from a higher voltage than the
output V
Power Supply, Shutdown, and Thermal
Considerations
The ISL55210 is intended for single supply operation from 3.0V
to 4.2V with an absolute maximum setting of 4.5V. The 3.3V
supply current is trimmed to be nominally 35mA at +25°C
ambient. Figure 27 shows the supply current for nominal +25°C
and -40°C to +85°C operation over the specified maximum
supply range. The input stage is biased from an internal voltage
referenced from the negative supply giving the exceptional 90dB
low frequency PSRR shown in Figure 25.
Since the input stage bias is from a re-regulated internal supply,
a simple approach to single +5V operation can be supported as
shown in Figure 32. Here, a simple IR drop from the +5V supply
will bring the operating supply voltage for the ISL55210 into its
allowed range. Figure 32 shows example calculations for the
voltage range at the ISL55210 +V
tolerance on the +5V supply and a 35mA to 55mA range on the
total supply current. Considering the 34mA to 44mA quiescent
current range from Figure 27 over the -40°C to +85°C ambient,
and the 3.4V to 4.4V supply voltage range assumed here, this is
designing for a 1mA to 11mA average load current which should
be adequate for most intended application loads. Good supply
decoupling at the device pins is required for this simple solution
to still provide exceptional SFDR performance.
CM
P-P
above the -V
CM
output capability. The V
CM
pin should be done with care in going towards the
setting.
CM
CM
up than down from the default value.
voltage be moved up to approximately 1.5V. This
S
S
supply). On the default 1.2V output V
supply is 2V so there is more room to move
CM
voltage down to 1.1V above the GND
CM
13
P-P
+0.5V. This would only occur if
CM
S
CM
reported in Figure 26 is an
pin assuming a ±5%
by applying a control voltage
from Figure 26. Operating
P-P
.
CM
ISL55210
on
CM
The ISL55210 includes a power shutdown feature that can be
used to reduce system power dissipation when signal path
operation is not required. This pin (PD) is referenced to the
ground pins and must be asserted low to activate the shutdown
feature. When not used, a 10kΩ external resistor to +V
be used to assert a high level at this pin. Digital control on this
pin can be either an open collector output (using that 10kΩ
pullup) or a CMOS logic line running off the same +V
amplifier. For split supply operation, the PD pins must be pulled
to below -V
Since the ISL55210 operates as a differential inverting op amp,
there is only modest signal path isolation when disabled as
shown in Figure 23. For small input signals, Figure 23 shows
about 5dB to 6dB isolation while for large signals, back to back
protection diodes across the inputs compress the signal to show
actually an improved isolation. This is intended to protect any
subsequent devices from large input signals during shutdown.
Those diodes limit the maximum overdrive voltage across the
input to approximately 0.5V in each polarity. The R
Test Circuit #1 limit the current into those diodes under this
condition.
The supply current in shutdown does not reduce to zero as
internal circuitry is still active to hold the output common mode
voltage at the V
the default value). This is intended to hold the ISL55210 output
near the desired common mode output level during shutdown.
This improves turn on characteristic and keeps the output
voltages in a safe range for downstream circuitry.
The very low internal power dissipation of the ISL55210, along
with the excellent thermal conductivity of the QFN package when
the exposed metal pad is tied to a conductive plate, reduces the
T
115mW dissipation and using the +63°C/W measured thermal
impedance from Junction to ambient, gives a rise of only
0.12 * 63 = +7.6°C. Operation at elevated ambient
temperatures is easily supported given this very low internal rise
to junction.
V
J
i
rise above ambient to very modest levels. Assuming a nominal
C
in
FIGURE 32. OPERATING FROM A SINGLE +5V SUPPLY
1:n
S
+ 0.54V to disable.
CM
control input voltage even during shutdown (or
R
R
G
G
35
V
CM
55mA
R
R
+5V ±5%
F
F
+
-
ISL55210
24.3
10k
3.4
+
10nF
2.2µF
PD
4.4V
G
S
resistors of
R
R
March 2, 2011
as the
O
S
O
should
FN7811.0
V
O