LT5554IUH#PBF Linear Technology, LT5554IUH#PBF Datasheet - Page 18

• Manufacturer Part Number: LT5554IUH#PBF
• Description: IC VGA DIG CONTROL 32-QFN
• Manufacturer: Linear Technology

Specifications of LT5554IUH#PBF

• Applications: Variable Gain (VGA)
• Number Of Circuits: 1
• -3db Bandwidth: 1GHz
• Current - Supply: 200mA
• Voltage - Supply, Single/dual (±): 4.75 V ~ 5.25 V
• Mounting Type: Surface Mount
• Package / Case: 32-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT5554
The PGx gain control inputs and STROBE input can be
confi gured to be either DC coupled or AC coupled depend-
ing on MODE pin level. The LT5554 gain control inputs
can be connected without external components to a wide
range of user control interfaces.
The LT5554 has internal overdrive protection circuitry.
The recovery time from a short duration (less than 5ns)
overdrive pulse is 5ns.
Input Interface
The DC voltage level at the IN
biased to about 2V when the part is either enabled or
disabled. The best linearity performance is achieved when
an input imbalance is less than 2dB.
Two typical Input connection circuits are shown in Figures
3 and 4.
An input source with 50Ω (5%) is required for best gain
error performance.
Decouple (DEC) Input
The DEC pin provides the DC voltage level for differential
inputs IN
charge/discharge the LT5554 input coupling capacitors
with about 30mA sourcing or sinking current capability.
APPLICATIONS INFORMATION
18
Figure 3. Input Capacitively-Coupled to a Differential Source
Figure 4. Input Transformer-Coupled to Single-Ended Source
V
SRC
R
50Ω
+
SRC
V
, IN
SRC
R
R
25Ω
25Ω
SRC/2
SRC/2
–
via an internal buffer, which is able to fast
•
•
0.1μF
C
C1
C2
DEC
0.1μF
C
DEC
+
, IN
DEC
IN
IN
–
+
–
DEC
IN
IN
inputs are internally
+
–
5554 F04
25Ω
25Ω
LT5554
5554 F03
25Ω
25Ω
LT5554
OUT
OUT
OUT
OUT
–
+
–
+
This buffer is also connected to the input resistive attenua-
tor network. The DEC pin is a ‘virtual ground’ and typically
connected to an external capacitor C
4). When C
attenuation for both differential mode and common mode
signals. The DEC pin de-coupling capacitor improves the
common mode AC performance even when the differential
IN
The DEC pin can be used as a voltage reference for external
circuitry when DC input coupling is desired.
Output Interface
The output interface must conduct the DC current of about
45mA to the amplifi er outputs (OUT
examples are shown in Figures 5 and 6.
A wide band ADC voltage interface is shown in Figure
5 where L1 and L2 are choke inductors. For a narrow
band application, a band pass fi lter can be placed at the
LT5554’s outputs.
DEC
IN
IN
+
DEC
+
–
IN
IN
, IN
MAX GAIN:
G
G
+
–
V
P
100Ω
R
MAX GAIN:
G
G
= 24dB
= 18dB
400Ω
OUT
V
P
–
Figure 6. Single-Ended Matched Output Interface
100Ω
LT5554
R
= 24dB
= 21dB
inputs are imbalanced by 3dB.
R
400Ω
OUT
LT5554
O
C5
R
OUT
OUT
O
DEC
Figure 5. Differential Output Interface
OUT
OUT
–
+
400Ω
is used, the LT5554 will have same input
–
+
R
O
400Ω
R
INDUCTORS
O
L1
CHOKE
R
133Ω
LOAD
R
133Ω
LOAD
L2
66.5Ω
C3
C4
5V
C5
R1
205Ω
205Ω
R5
R6
V
CCO
5V
+
OUT
R2
66.5Ω
DEC
R
100Ω
SADC
•
•
MAX GAIN INTO Z
G
4:1
T2
P
V
–
= 18dB
CCO
). Two interface
(Figures 3 and
C6
•
ADC
5554 F06
ADC
BIAS
O
:
Z
50Ω
O
5554 F05
5554f