MC33501_06 Datasheet, PDF (6/14 Pages) ON Semiconductor – 1.0 V, Rail−to−Rail, Single Operational Amplifiers

MC33501, MC33503
General Information
The MC33501/503 dual operational amplifier is unique in
its ability to provide 1.0 V rail−to−rail performance on both
the input and output by using a SMARTMOSt process. The
amplifier output swings within 50 mV of both rails and is
able to provide 50 mA of output drive current with a 5.0 V
supply, and 10 mA with a 1.0 V supply. A 5.0 MHz
bandwidth and a slew rate of 3.0 V/ms is achieved with high
speed depletion mode NMOS (DNMOS) and vertical PNP
transistors. This device is characterized over a temperature
range of −40°C to 105°C.
Circuit Information
Input Stage
One volt rail−to−rail performance is achieved in the
MC33501/503 at the input by using a single pair of depletion
mode NMOS devices (DNMOS) to form a differential
amplifier with a very low input current of 40 fA. The normal
input common mode range of a DNMOS device, with an ion
implanted negative threshold, includes ground and relies on
the body effect to dynamically shift the threshold to a
positive value as the gates are moved from ground towards
the positive supply. Because the device is manufactured in
a p−well process, the body effect coefficient is sufficiently
large to ensure that the input stage will remain substantially
saturated when the inputs are at the positive rail. This also
applies at very low supply voltages. The 1.0 V rail−to−rail
input stage consists of a DNMOS differential amplifier, a
folded cascode, and a low voltage balanced mirror. The low
voltage cascaded balanced mirror provides high 1st stage
gain and base current cancellation without sacrificing signal
integrity. A common mode feedback path is also employed
to enable the offset voltage to track over the input common
mode voltage. The total operational amplifier quiescent
current drop is 1.3 mA/amp.
Output Stage
An additional feature of this device is an “on demand”
base current cancellation amplifier. This feature provides
base drive to the output power devices by making use of a
buffer amplifier to perform a voltage−to−current
conversion. This is done in direct proportion to the load
conditions. This “on demand” feature allows these
amplifiers to consume only a few micro−amps of current
when the output stage is in its quiescent mode. Yet it
provides high output current when required by the load. The
rail−to−rail output stage current boost circuit provides
50 mA of output current with a 5.0 V supply (For a 1.0 V
supply output stage will do 10 mA) enabling the operational
amplifier to drive a 600 W load. A buffer is necessary to
isolate the load current effects in the output stage from the
input stage. Because of the low voltage conditions, a
DNMOS follower is used to provide an essentially zero
voltage level shift. This buffer isolates any load current
changes on the output stage from loading the input stage. A
high speed vertical PNP transistor provides excellent
frequency performance while sourcing current. The
operational amplifier is also internally compensated to
provide a phase margin of 60 degrees. It has a unity gain of
5.0 MHz with a 5.0 V supply and 4.0 MHz with a 1.0 V
supply.
Low Voltage Operation
The MC33501/503 will operate at supply voltages from
0.9 to 7.0 V and ground. When using the MC33501/503 at
supply voltages of less than 1.2 V, input offset voltage may
increase slightly as the input signal swings within
approximately 50 mV of the positive supply rail. This effect
occurs only for supply voltages below 1.2 V, due to the input
depletion mode MOSFETs starting to transition between the
saturated to linear region, and should be considered when
designing high side dc sensing applications operating at the
positive supply rail. Since the device is rail−to−rail on both
input and output, high dynamic range single battery cell
applications are now possible.
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