VRE117 데이터 시트보기 (PDF) - Cirrus Logic
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VRE117 Datasheet PDF : 5 Pages
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VRE117/119
Product Innovation From
3. THEORY OF OPERATION
The following discussion refers to the block diagram in Figure 1. A FET current source is used to bias a 6.3 V zener
diode. The zener voltage is divided by the resistor network R1 and R2. This voltage is then applied to the noninvert-
ing input of the operational amplifier which amplifies the voltage to produce a 3 V output. The gain is determined by
the resistor networks R3 and R4: G=1 + R4/R3. The 6.3 V zener diode is used because it is the most stable diode
over time and temperature.
The current source provides a closely regulated zener current, which determines the slope of the reference’s volt-
age vs. temperature function. By trimming the zener current, a lower drift over temperature can be achieved. But
since the voltage vs. temperature function is nonlinear, this method leaves a residual error over wide temperature
ranges.
To remove this residual error, a nonlinear compensation network of thermistors and resistors is used in the
VRE117/119 series references. This proprietary network eliminates most of the nonlinearity in the voltage vs. tem-
perature function. By then adjusting the slope, The VRE117/119 series produces a very stable voltage over wide
temperature ranges. This network is less than 2% of the overall network resistance so it has a negligible effect on
long term stability.
4. APPLICATION INFORMATION
The proper connection of the VRE117 series voltage reference with the optional trim resistors is shown below. When
trimming the VRE119, the positive voltage should be trimmed first since the negative voltage tracks the positive
side. Pay careful attention to the circuit layout to avoid noise pickup and voltage drops in the lines.
The VRE117/119 series voltage references have the ground terminal brought out on two pins (pin 6 and pin 7) which
are connected together internally. This allows the user to achieve greater accuracy when using a socket. Voltage
references have a voltage drop across their power supply ground pin due to quiescent current flowing through the
contact resistance. If the contact resistance was constant with time and temperature, this voltage drop could be
trimmed out. When the reference is plugged into a socket, this source of error can be as high as 20 ppm. By con-
necting pin 7 to the power supply ground and pin 6 to a high impedance ground point in the measurement circuit,
the error due to the contact resistance can be eliminated. If the unit is soldered into place the contact resistance is
sufficiently small that it doesn’t effect performance.
EXTERNAL CONNECTIONS
1. Optional Fine Adjust for approximately ±5mV.
PIN CONFIGURATION
TOP VIEW
NC
NC
NC
-PS
NC
REF. GND
GND
VRE117
FINE ADJ.
+3.0V (-3.0V)
FINE ADJ.
+PS (-PS)
NC
NC
NC
4
TOP VIEW
FINE -ADJ.
-3.0V
FINE -ADJ.
-PS
NC
REF. GND
GND
VRE119
FINE +ADJ.
+3.0V
FINE +ADJ.
+PS
NC
NC
NC
VRE117DS
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