MC33502 Datasheet, PDF (5/15 Pages) ON Semiconductor – LOW VOLTAGE RAIL-TO-RAIL DUAL OPERATIONAL AMPLIFIER

MC33502
GENERAL INFORMATION
The MC33502 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 SMARTMOS 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/µs 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
MC33502 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 substantually
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 cascoded balanced mirror provides high 1st stage
gain and base current cancellation without sacrificing signal
integrity. Also, the input offset voltage is trimmed to less than
1.0 mV because of the limited available supply voltage. The
body voltage of the input DNMOS differential pair is internally
trimmed to minimize the input offset voltage. 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 Ω 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 MC33502 will operate at supply voltages from 0.9 to
7.0 V and ground. When using the MC33502 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.
MOTOROLA ANALOG IC DEVICE DATA
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