Application Hints (Continued)
4.0 VREF AND VTEMP CAPACITIVE LOADING
01289319
FIGURE 4. Loading of VREF and VTEMP
The LM56 VREF and VTEMP outputs handle capacitive load-
ing well. Without any special precautions, these outputs can
drive any capacitive load as shown in Figure 4 .
6.0 APPLICATIONS CIRCUITS
5.0 NOISY ENVIRONMENTS
Over the specified temperature range the LM56 VTEMPout-
put has a maximum output impedance of 1500Ω. In an
extremely noisy environment it may be necessary to add
some filtering to minimize noise pickup. It is recommended
that 0.1 µF be added from V+ to GND to bypass the power
supply voltage, as shown in Figure 4 . In a noisy environment
it may be necessary to add a capacitor from the VTEMP
output to ground. A 1 µF output capacitor with the 1500Ω
output impedance will form a 106 Hz lowpass filter. Since the
thermal time constant of the VTEMP output is much slower
than the 9.4 ms time constant formed by the RC, the overall
response time of the VTEMP output will not be significantly
affected. For much larger capacitors this additional time lag
will increase the overall response time of the LM56.
01289320
FIGURE 5. Reducing Errors Caused by Bias Current
The circuit shown in Figure 5 will reduce the effective bias
current error for VT2 as discussed in Section 3.0 to be
equivalent to the error term of VT1. For this circuit the effect
of the bias current on the first trip point can be defined by the
following equations:
where IB = 300 nA (the maximum specified error).
Similarly, bias current affect on VT2 can be defined by:
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