OFFSET VOLTAGE ERROR CALCULATION
The offset voltage (VOS) of the OPA51 and OPA552 is
calculate excursions from the specified offset voltage
under different applications conditions. For example, a
common application might configure the amplifier with
a –48 single supply with –6V common-mode. This
configuration represents a 12V variation in power sup-
ply: ±30V or 60V in the offset specification versus 48V
in the application. In addition, this configuration has an
18V variation in common-mode voltage: VS/2 = –24V is
the specification for these power supplies, but the com-
mon-mode voltage is –6V in the application.
specified with a ±30V power supply and the common-
mode voltage centered between the supplies (VS/2 =
0V). Additional specifications for power supply rejec-
tion and common-mode rejection are provided to allow
the user to easily calculate worst-case excepted offset
under the conditions of a given application.
Power Supply Rejection Ratio (PSRR) is specified in
µV/V. For the OPA551 and OPA552, worst-case PSRR
is 30µV/V, which means for each volt of change in total
power supply voltage, the offset may shift by up to
30µV/V. Common-Mode Rejection Ratio (CMRR) is
specified in dB, which can be converted to µV/V using
the following equation:
Calculation of the worst-case expected offset would be
as follows:
Worst-case VOS
=
(2)
maximum specified VOS
CMRR in (V/V) = 10[(CMRR in dB)/–20]
(1)
+ (power supply variation • PSRR
+ (common-mode variation • CMRR)
For the OPA551 and OPA552, the worst-case CMRR at
±30mV supply over the full common-mode range is
96dB, or approxmately 15.8µV/V. This means that for
every volt of change in common-mode, the offset may
shift up to 15.8µV. These numbers can be used to
VOSwc = 5mV + (12V • 30µV/V) + (18V • 15.8µV/V)
= ±5.64mV
OPA551, OPA552
14
SBOS100A
www.ti.com
TI [ TEXAS INSTRUMENTS ]
