lt5524 Linear Technology Corporation, lt5524 Datasheet - Page 14

• Manufacturer Part Number: lt5524
• Description: Low Distortion If Amplifier/adc Driver With Digitally Controlled Gain
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT5524
Application (Demo) Boards
The LT5524 demo boards are provided in the versions
shown in Figure 10 (with output transformer) and Fig-
ure 11 (without output transformer). All I/O signal ports
are matched to 50Ω. Moreover, 40k resistors (not shown)
connect all five control pins (EN, PGA0, PGA1, PGA2,
PGA3) to V
mum gain state.
The gain setting can be changed by connecting the control
pins to ground. Test points (TP1, TP2, TP3) are provided
to monitor the input and output DC bias voltage. Jumper
J1 can be removed when differential input is desired, but
in that case, T1 should be changed to a 1:1 center-tap
transformer to preserve 50Ω input matching. The demo
board is shipped with optional output back-matching
resistor R
R
The Output Transformer Application Board (Figure 10) is
one example of an output impedance transformation
14
OUT
= 100Ω, presented to the LT5524.
RESISTIVE DEMO BOARD
DIFFERENTIAL OUTPUT
IN
IF
MATCH
CC
, such that the LT5524 is shipped in maxi-
= 255Ω. This results in a net output load,
J1
0Ω
U
1:2
TC2-1T
T1
V
Figure 11. Wideband Differential Output Application Board (Simplified Schematic)
CC
U
C1
0.47µF
C2
0.1µF
PGA0
W
PGA1
EN
10
1
2
3
4
5
6
7
8
9
EN
V
GND
GND
IN
IN
GND
GND
PGA0
PGA1
CC1
+
–
U
LT5524
PGA3
PGA2
OUT
OUT
V
GND
GND
GND
GND
CC2
NC
–
+
20
19
18
17
16
15
14
13
12
11
PGA2 PGA3
NC
(T2 transformer). For the Typical Performance Character-
istics curves, all linearity tests are performed on this
board. By removing R
= 200Ω can be evaluated (provided the lack of impedance
back-matching is suitably remedied).
The transformer board can provide a differential output
when Jumper J2 is removed.
The Wideband Differential Output Application Board (Fig-
ure 11) is an example of direct coupling (no transformer)
to the load, and has wider output bandwidth. This board
gives direct access to the LT5524’s output pins, and was
used for stability tests. Higher V
compensate for the DC voltage drop on R1 and R2. Use
TP2, TP3 to monitor the actual LT5524 output bias volt-
age. By replacing R1 and R2 with inductors, this board can
operate with a 5V supply. However, this may limit the
minimum signal frequency. For example, an 820nH choke
inductor will limit the lowest signal frequency to 40MHz.
R
50Ω
OUT
R1
50Ω
R2
50Ω
MATCH
47nF
47nF
, the performance with R
C5
C6
C4
0.1µF
OSUP
0PEN
R
100Ω
J2
(6.5V) is required to
C3
4.7µF
LOAD
V
OSUP
OUT
IF
5524 F11
OUT
5524f