LDO Input | LDO Output | Output Noise Level |
---|---|---|
Vin+ > 6V | 5.2V | 27µVRMS |
Vin– < –5V | –200mV | 22µVRMS |
This design shows a power supply that can be used to create a positive operational-amplifier (op amp) supply and a small negative op-amp supply. This small negative voltage is adjustable and is necessary in many operational amplifiers to verify linearity down to ground. This design shows the TPS7A3901 as the power supply for creating the positive and negative voltage rails for operational amplifier circuits. This low dropout regulator (LDO) differs from most in the ability to regulate small negative voltages, as the following image shows. This is a generic circuit implementation that can be used in many Industrial applications.
Parameter | Test Condition | Data Sheet Specification | Measured ADS8900B Performance |
---|---|---|---|
SNR | Vin_max = 5V, Vin_min = 0V | 104.5dB | 102.2dB |
THD | Vin_max = 5V, Vin_min = 0V | –125dB | –123.5dB |
Desired Output | R1 | R2 |
---|---|---|
+5.2V | 34kΩ | 10kΩ |
–200mV | 1.69kΩ | 10kΩ |
The FFT in the following was measured with an input signal very near full scale ±5V (–0.2dBFS). Note that the SNR and THD is very good compared to the case where the supply is adjusted to 5V and GND. Note the TPS7A3901 is a convenient way to generate a linear –0.2-V supply.
The FFT shown in the following image was measured with an input signal very near full scale ±5V (–0.2dBFS). Note that the SNR and THD is poor compared to the case where the supply is adjusted to 5.2V and –0.2V.
Device | Key Features | Link | Similar Devices |
---|---|---|---|
TPS7A3901 | The TPS7A39 device is a dual, monolithic, high-PSRR, positive and negative low-dropout (LDO) voltage regulator capable of sourcing (and sinking) up to 150mA of current. The device has a wide output voltage range of 1.2V to 30V for the positive output and –30V to 0V for the negative output. This device is an excellent choice for generating a small negative supply voltage that is useful in cases where a single-supply amplifier needs a small negative supply so that the output can linearly swing to 0V. | www.ti.com/product/TPS7A39 | www.ti.com/product/LM7705(1) |
ADS8900B | Bipolar differential inputs, SAR ADC with internal reference buffer, SPI interface | www.ti.com/product/ADS8900B | www.ti.com/adcs |
OPA320 | Precision, Zero-Crossover, 20Mhz, RRIO, CMOS Operational Amplifier | www.ti.com/product/opa320 | www.ti.com/opamp |
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