Datasheet

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Single-Supply Operation (3 V to 5 V)
( )
W
--
=
-+
k50
VVV2
I
SSCM
EXT
(2)
V
S+
CM
V
S–
50kW
tointernal
CMcircuit
I
EXT
50kW
Powerdown Operation: Device
V
S+
CM
V
Signal
V
S–
R
F
R
F
R
G
R
G
R
T
R
O
R
O
V
OUT+
V
OUT-
THS4520
V
Bias
= V
CM
R
S
R
T
V
CM
V
CM
V
CM
V
CM
R
S
( )
÷
÷
ø
ö
ç
ç
è
æ
+-
÷
÷
ø
ö
ç
ç
è
æ
-
=
+
FIN
IC
F
CM
SIC
PU
R
1
R
1
V
R
1
V
VV
R
(3)
THS4520
SLOS503B – SEPTEMBER 2006 – REVISED JULY 2007
required for best performance, but it is intended to be
a DC bias input pin. Bypass capacitors are
To facilitate testing with common lab equipment, the
recommended on this pin to reduce noise at the
THS4520 EVM allows split-supply operation, and the
output. The external current required to overdrive the
characterization data presented in this data sheet
internal resistor divider is given by Equation 2 :
was taken with split-supply power inputs. The device
can easily be used with a single-supply power input
without degrading the performance. Figure 62 ,
Figure 63 , and Figure 64 show DC and AC-coupled
single-supply circuits with single-ended inputs. These
where V
CM
is the voltage applied to the CM pin.
configurations all allow the input and output
common-mode voltage to be set to mid-supply
allowing for optimum performance. The information
presented here can also be applied to differential
input sources.
In Figure 62 , the source is referenced to the same
voltage as the CM pin (V
CM
). V
CM
is set by the
internal circuit to mid-supply. R
T
along with the input
impedance of the amplifier circuit provides input
termination, which is also referenced to V
CM
.
Note R
S
and R
T
are added to the alternate input from
the signal input to balance the amplifier. Alternately,
Figure 61. CM Input Circuit
one resistor can be used equal to the combined
value R
G
+ R
S
||R
T
on this input. This is also true of
the circuits shown in Figure 63 and Figure 64 .
Enable/Disable Thresholds
The enable/disable thresholds of the THS4520 are
dependent upon the power supplies, and the
thresholds are always referenced to the lower power
supply rail. The device is enabled or disabled for the
following conditions:
• Device enabled: V
PD
> V
S-
+ 0.8 x (V
S+
- V
S-
)
• Device disabled: V
PD
< V
S-
+ 0.2 x (V
S+
- V
S-
)
If the PD pin is left open, the device will default to the
enabled state.
Table 3 shows the thresholds for some common
Figure 62. THS4520 DC Coupled Single-Supply
power supply configurations:
with Input Biased to V
CM
Table 3. Power Supply Configurations
In Figure 63 the source is referenced to ground and
so is the input termination resistor. R
PU
is added to
Enable Disable
Power Supply
Threshold Threshold Comment
the circuit to avoid violating the V
ICR
of the op amp.
(V
S+
, V
S-
)
(V) (V)
The proper value of resistor to add can be calculated
Shown in data
from Equation 3 :
± 2.5 V 1.5 -1.5
table
Shown in data
± 1.65 V 1 -1
table
Split, unbalanced
(4 V , -1 V) 3 0
supplies
Single-sided
V
IC
is the desired input common-mode voltage,
(5 V, gnd) 4 1
supply
V
CM
= CM, and R
IN
= R
G
+ R
S
||R
T
. To set to
Single-sided
mid-supply, make the value of R
PU
= R
G
+ R
S
||R
T
.
(3.3 V, gnd) 2.64 0.66
supply
Single-sided
(3 V, gnd) 2.4 0.6
supply
22
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