lmp7312max National Semiconductor Corporation, lmp7312max Datasheet - Page 15

• Manufacturer Part Number: lmp7312max
• Description: Lmp7312 Precision Spi-programmable Afe With Differential/single-ended Input/output
• Manufacturer: National Semiconductor Corporation

INPUT VOLTAGE RANGE
The LMP7312 has an internal OpAmp with rail-to-rail input
voltage range capability. The requirement to stay within the
V
age Range specification as explained in this application sec-
tion.
Differential Output
Considering a single positive supply (V
Input Common mode voltage, V
the Attenuation inputs and V
Amplification inputs, has to stay between the MIN and MAX
values determined by these formulas:
CM
CM
K
Regardless to the values derived by the formula, the voltage
on each input pin must never exceed the specified Absolute
Maximum Ratings.
Below are some typical values:
Differential Input, Differential Output, V
* Limited by the operating ratings on input pins
In the case of a single ended input referred to ground (-V
GND, -IN = GND) the table below summarizes the voltage
range allowed on the +VI
Single Ended Input, Differential Output, V
2.5V, -V
* Limited by the operating ratings on input pins
** Limited by the output voltage swing (0.2V to V
-V
Single Ended Output
In this mode the LMP7312 behaves as a Difference Amplifier,
with -V
volt differential input signal is applied. The voltages at the
OpAmp inputs are determined by +V
The voltage range of +V
V
Gain 0.096 V/
K
-
V
MAX
OUT
V
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
and V
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
is a function of the Gain according to the table below:
MAX
MIN
)
1 V/V
2 V/V
Gain
1 V/V
2 V/V
Gain
= V
OUT
V
0.12
= -1/K
= V
IN
+
S
rail at the OpAmp input translates in an Input Volt-
/V
= GND, -I
+ 1/ K
S
R
+ 1/K
V
being the reference output voltage when a zero
*V
OCM
-12 V
V
0.192 V/
V
0.218
-15 V
-15 V
-6 V
V
-11.5 V
Min
* (V
-15 V
-3.1 V
*(V
-6 V
Min
IN
**
**
S
= GND
S
*
*
V
+V
– (-V
- V
*
IN
CM_ATT
N
IN
and +I
and +I
OCM
0.384 V/
V
0.414
+12 V
+15 V
+15 V
+6 V
CM_AMP
Max
OUT
+15 V
+8.1 V
+15 V
+11 V
)
Max
CM_ATT
/V
**
IN
IN
**
*
*
R
inputs is as follows:
inputs.
IN
))
*
= (+I
0.768 V/
V
0.806
and -V
-
-4.6 V
-2.3 V
S
= (+V
-0.2V on both + V
= GND, V
Min
-2.3 V
-1.2 V
S
IN
Min
= 5V, V
+ (-I
OUT
S
IN
**
**
V
= 5V, V
+IN
+ (-V
CM_AMP
1 V/V 2 V/V
1.065 2.096
/V
IN
))/2 for the
OCM
+
R
+4.6 V
+2.3 V
= V
voltages.
+7.3 V
+6.2 V
IN
Max
Max
OCM
))/2 for
= 2.5V
OUT
S
) the
IN
**
**
and
=
=
15
V
Regardless of the values derived by the formula, the voltage
on each input pin must never exceed the specified Absolute
Maximum Ratings.
Below are some typical values:
Differential Input, Single Ended Output, V
GND, and -V
* Limited by the operating ratings on input pins
In the case of a single ended input referred to ground (-V
GND, -IN = GND) this table summarize the voltage ranges
allowed on the +V
Single Ended Input, Single Ended Output, V
= GND, -V
* Limited by the operating ratings on input pins
** Limited by the output voltage swing (0.2V to V
SERIAL INTERFACE CONTROL OPERATION
The serial interface control of the LMP7312 can be supplied
with a voltage between 2.7V and 5.5V through the V
compatibility with different logic families present in the market.
The LMP7312 Attenuation, Amplification, Null switch and HiZ
modes are controlled by a register. Data to be written into the
control register is first loaded into the LMP7312 via the serial
interface. The serial interface employs a 5-bit shift register.
Data is loaded through the serial data input, SDI. Data pass-
ing through the shift register is obtained through the serial
data output, SDO. The serial clock, SCK controls the serial
loading process. All five data bits are required to correctly
program the device. The falling edge of CS enables the shift
register to receive data. The SCK signal must be high during
the falling edge of CS. Each data bit is clocked into the shift
register on the rising edge of SCK. Data is transferred from
the shift register to the holding register on the rising edge of
CS. Operation is shown in the timing diagram .
SPI Registers
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
1 V/V
2 V/V
MIN
0.096 V/V
0.192 V/V
0.384 V/V
0.768 V/V
Gain_1
MSB
Gain
= -1/K
1 V/V
2 V/V
Gain
OUT
V
* (-V
OUT
/V
Gain_0
-15 V
-11.5 V
-6 V
-3 V
R
/V
OUT
= 2.5V, -V
-11.5 V
IN
Min
R
-15 V
-3.1 V
**
**
Min
-6 V
and +I
= 2.5V
*
/V
R
+V
)
*
+V
*
IN
EN_CL
IN
+15 V
+12 V
+6 V
+3 V
IN
IN
inputs.
Max
= GND, -I
+15 V
+8.1 V
+15 V
+11 V
**
**
Max
*
**
*
Null_SW
-2.3 V
-1.1 V
S
IN
-0.2V on +V
Min
-2.3 V
-1.2 V
= GND
Min
**
**
S
= 5V, V
S
+I
+I
www.national.com
= 5V, V
IN
+2.3 V
+1.1 V
OUT
IN
Hi_Z
LSB
+7.3 V
+6.2 V
IO
Max
Max
)
OCM
pin for
**
**
OCM
IN
=
=