LMH6517 Datasheet, PDF (24/34 Pages) National Semiconductor (TI) – Multi Standard, IF and Baseband, Dual, DVGA

LMH6517
SNOSB19K – NOVEMBER 2008 – REVISED MARCH 2013
C7
1= read
0=write
C6
0
Table 3. Serial Word Format for LMH6517
C5
0
C4
0
C3
0
C2
0
C1
0
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C0
0=Ch A
1=Ch B
Enable
1=On
0=Off
Gb5
1=+16dB
Table 4. Serial Word Format for LMH6517 (cont)
Gb4
1=+8dB
Gb3
1=+4dB
Gb2
1=+2dB
Gb1
1=+1dB
Gb0
1=+0.5dB
RES
0
PULSE MODE (MOD1= 0, MOD0 = 1)
Pulse mode is a simple yet fast way to adjust gain settings. Using only two control lines per device the LMH6517
gain can be changed by simple up and down signals. Gain steps are selectable either by hard wiring the board
or using two additional logic inputs. For a system where gain changes can be stepped from one gain to the next
and where board space is limited this mode may be the best choice. The ENA and ENB pins are fully active
during pulse mode, and the channel gain state is preserved during the disabled state. See Typical Performance
Characteristics for disable and enable timing information.
DNA
1
UPA
2
GND
3
GND
4
+3.3/NC
5
GND
6
UPB
7
DNB
8
LMH6517
GND
24
OPA+
23
OPA-
22
ENA
21
GND
20
GND
19
ENB
18
OPB-
17
OPB+
Figure 55. Pin Functions for Pulse Mode
The LMH6517 supports a simple pulse up or pulse down control mode. In this mode the gain step size can be
selected from a choice of 0.5, 1, 2 or 6dB steps. In operation the gain can be quickly adjusted either up of down
one step at a time by a negative pulse on the UP or DN pins. This mode of operation is most suitable for
applications where board space is at a premium and high speed gain changes are desired. As shown in
Figure 56 each gain step pulse must have a logic high state of at least t_PW= 20 ns and a logic low state of at
least t_PG 20 ns for the pulse to register as a gain change signal.
To provide a known gain state there is a reset feature in pulse mode. To reset the gain to maximum gain both
the UP and DN pins must be strobed low together as shown in Figure 56. There must be an overlap of at least
t_RW= 20 ns for the reset to register.
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