lt5554 Linear Technology Corporation, lt5554 Datasheet - Page 14

• Manufacturer Part Number: lt5554
• Description: Broadband Ultra Low Distortion 7-bit Digitally Controlled Vga
• Manufacturer: Linear Technology Corporation

LT5554
PIN FUNCTIONS
When the MODE pin is left open, the PGx inputs are AC-
couple and the STROBE input is DC-coupled.
In DC-coupled mode, the PGx and STROBE inputs levels are
0.6V and 2.2V. In AC-coupled mode, the PGx and STROBE
inputs are driven with 0.6V
rise and fall time <5ns) regardless the DC voltage level. A
positive transition sets a High-state. A negative transition
sets a Low-state (for PGx and STROBE inputs).
OUT
with a center tap tied to V
mended to conduct the DC quiescent current.
OUT
with a center tap tied to V
mended to conduct the DC quiescent current.
ENB (Pin 23): Enable Pin for Amplifi er. When the ENB
input voltage is higher than 3V, the amplifi er is turned on.
BLOCK DIAGRAM
14
–
+
(Pin 20): Positive Amplifi er Output Pin. A transformer
(Pin 21): Negative Amplifi er Output Pin. A transformer
3
4
5
6
DEC
IN
IN
DEC
CC
CC
+
–
PG6
P-P
or a choke inductor is recom-
or a choke inductor is recom-
ATTENUATOR
12dB RANGE
11
GAIN LOGIC
4dB STEPS
(15 PINS)
minimum amplitude (with
PG5
GND
ATTENUATOR
9
MODE
Figure 1. Functional Block Diagram
18
V
R
25Ω
R
25Ω
CC
IN
IN
+
–
STROBE
STROBE
MODE
LOGIC
17
REGULATOR
AND BIAS
VOLTAGE
14
V
CC
24
PG4
When the ENB input voltage is less than or equal to 0.6V,
the amplifi er is turned off.
PG4 (Pin 27): 2dB Step Amplifi er Programmable Gain Con-
trol Input Pin. Input levels are controlled by MODE pin.
PG3 (Pin 29): 1dB Step Amplifi er Programmable Gain Con-
trol Input Pin. Input levels are controlled by MODE pin.
PG2 (Pin 30): 0.5dB Step Amplifi er Programmable Gain Con-
trol Input Pin. Input levels are controlled by MODE pin.
PG1 (Pin 32): 0.25dB Step Amplifi er Programmable
Gain Control Input Pin. Input levels are controlled by
MODE pin.
EXPOSED PAD (Pin 33): Ground. This pin must be sol-
dered to the printed circuit board ground plane for good
heat dissipation.
27
AMPLIFIER
PG3
TRANSCONDUCTANCE
29
3.875dB RANGE
0.125dB STEPS
PG2
GAIN LOGIC
ENB
CONTROL
ENABLE
30
23
PG1
32
R
400Ω
O
PG0
12
OUT
OUT
5554 BD
–
+
21
20
5554f