LTC6252 Linear Technology, LTC6252 Datasheet - Page 14

• Manufacturer Part Number: LTC6252
• Description: 3.5mA Power Efficient Rail-to-Rail I/O Op Amps
• Manufacturer: Linear Technology

DataSheet.in
APPLICATIONS INFORMATION
LTC6252/LTC6253/LTC6254
Input Offset Voltage
The offset voltage will change depending upon which
input stage is active. The PNP input stage is active from
the negative supply rail to approximately 1.2V below the
positive supply rail, then the NPN input stage is activated
for the remaining input range up to the positive supply
rail with the PNP stage inactive. The offset voltage mag-
nitude for the PNP input stage is trimmed to less than
350μV with 5V total supply at room temperature, and is
typically less than 150μV. The offset voltage for the NPN
input stage is less than 2.2mV with 5V total supply at
room temperature.
Input Bias Current
The LTC6252 family uses a bias current cancellation cir-
cuit to compensate for the base current of the PNP input
pair. This results in a typical I
input common mode voltage is less than 200mV, the bias
cancellation circuit is no longer effective and the input
bias current magnitude can reach a value above 4μA. For
common mode voltages ranging from 0.2V above the
negative supply to 1.2V below the positive supply, the
low input bias current allows the amplifi ers to be used in
applications with high source resistances where errors
due to voltage drops must be minimized.
Output
The LTC6252 family has excellent output drive capability.
The amplifi ers can typically deliver 90mA of output drive
current at a total supply of 5V. The maximum output
current is a function of the total supply voltage. As the
supply voltage to the amplifi er decreases, the output
current capability also decreases. Attention must be paid
to keep the junction temperature of the IC below 150°C
(refer to the Power Dissipation Section) when the output
is in continuous short-circuit. The output of the amplifi er
has reverse-biased diodes connected to each supply. If
the output is forced beyond either supply, extremely high
current will fl ow through these diodes which can result
in damage to the device. Forcing the output to even 1V
beyond either supply could result in several hundred mil-
liamps of current through either diode.
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B
of about 100nA. When the
Input Protection
The LTC6252/LTC6253/LTC6254 input stages are protected
against a large differential input voltage of 1.4V or higher by
2 pairs of back-to-back diodes to prevent the emitter-base
breakdown of the input transistors. In addition, the input
and shutdown pins have reverse biased diodes connected
to the supplies. The current in these diodes must be limited
to less than 10mA. The amplifi ers should not be used as
comparators or in other open loop applications.
ESD
The LTC6252 family has reverse-biased ESD protection
diodes on all inputs and outputs as shown in Figure 1.
There is an additional clamp between the positive and nega-
tive supplies that further protects the device during ESD
strikes. Hot plugging of the device into a powered socket
must be avoided since this can trigger the clamp resulting
in larger currents fl owing between the supply pins.
Capacitive Loads
The LTC6252/LTC6253/LTC6254 are optimized for high
bandwidth and low power applications. Consequently they
have not been designed to directly drive large capacitive
loads. Increased capacitance at the output creates an ad-
ditional pole in the open loop frequency response, wors-
ening the phase margin. When driving capacitive loads, a
resistor of 10Ω to 100Ω should be connected between the
amplifi er output and the capacitive load to avoid ringing
or oscillation. The feedback should be taken directly from
the amplifi er output. Higher voltage gain confi gurations
tend to have better capacitive drive capability than lower
gain confi gurations due to lower closed loop bandwidth
and hence higher phase margin. The graphs titled Series
Output Resistor vs Capacitive Load demonstrate the tran-
sient response of the amplifi er when driving capacitive
loads with various series resistors.
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