Making certain secure energy administration is essential in fashionable electronics, and the facility provide rejection ratio (PSRR) performs a key function in attaining this. This text serves as a sensible information to measuring PSRR for energy administration ICs (PMICs) and providing clear and complete directions.
PSRR displays a circuit’s means to reject fluctuations in its energy provide voltage, instantly impacting efficiency and reliability. By understanding and precisely measuring this parameter, engineers can design extra strong methods that preserve constant operation even below various energy circumstances.
Determine 1 Right here is the overall methodology to measure PSRR. Supply: Renesas
PSRR is an important parameter that assesses an LDO’s functionality to take care of a constant output voltage amidst variations within the enter energy provide. Attaining excessive PSRR is essential in situations by which the enter energy provide experiences fluctuations, thereby making certain the dependability of the output voltage. Determine 1 under illustrates the overall methodology for measuring PSRR.
The mathematical expression to calculate the PSRR worth is:
PSRR = 20 log10 VIN/VOUT
The place VIN and VOUT are the AC ripple of the enter and output voltage, respectively.
Tools and setup
To make sure an correct measurement of the PSRR, it’s important to arrange the check setting with precision. The next design outlines using the listed tools to ascertain a sturdy and dependable check configuration.
First, join the facility provide—in our case it’s a Keithley 2460—to the enter of the Picotest J2120A line injector. The facility provide ought to be configured to generate a secure DC voltage whereas the AC ripple element is offered by a Bode 100 community analyzer output utilizing the J2120A line injector to simulate energy provide variations.
Notice that J2120A line injector consists of an internally biased N-channel MOSFET. This implies that there’s a voltage drop between the J2120A enter and output. The voltage drop is non-linear, and its dependency is proven on Determine 2. Which means that every time the load present is adjusted, the supply energy provide should even be adjusted to take care of a continuing DC output voltage on the J2120A terminals.
Determine 2 J2120A’s resistance and voltage drop is proven versus output present. Supply: Renesas
For instance, to get 1.2 V on the enter of the LDO regulator, and relying on the present load, it is perhaps required to set the voltage on the enter of the road injector from 2.5 V to three.5 V. The MOSFET operates as open loop so to not change into unstable when related to the exterior regulator.
Subsequent, a digital multimeter is used to observe each the enter and output voltages of the PMIC. Be sure that correct grounding is used, and minimal interference is current within the connections to take care of measurement integrity.
Lastly, a Bode 100 from Omicron Lab is used to report and analyze the measurements. This knowledge can be utilized to compute the PSRR values and consider the PMIC’s means to take care of a secure output regardless of variations within the enter provide.
By fastidiously following this setup, one can guarantee correct and dependable PSRR measurements, contributing to the event of high-performance and reliable digital methods.
Desk 1: Right here is a top level view of the devices utilized in PSRR measurements. Supply: Renesas
Desk 2 See the check circumstances for LDOs. Supply: Renesas
Settings for PSRR bench measurements setup
Determine 3 Block diagram reveals the important thing constructing blocks of PSRR bench measurement. Supply: Renesas
The PSRR measurement is carried out with the Bode 100. The Achieve/Section measurement sort ought to be chosen within the Bode Analyzer Suite software program as proven on Determine 4.
Determine 4 Begin menu is proven within the Bode Analyzer Suite software program. Supply: Renesas
Set the Hint 1 format to Magnitude (dB).
Determine 5 That is set Hint 1. Supply: Renesas
To get the goal PSRR measurement, select the next settings within the “{Hardware} Setup”:
- Frequency: Change the Begin frequency to “10 Hz” and Cease frequency to “10 MHz”.
- Supply mode: Select between Auto off or At all times on. In Auto off mode, the supply will likely be robotically turned off each time it’s not used (when a measurement is stopped). In At all times on mode, the sign supply stays on after the measurement has completed. Which means that the final frequency level in a sweep measurement defines the sign supply frequency and stage.
- Supply stage: Set the fixed supply stage to “-16 dB” or larger for the output stage. The unit could be modified within the choices. By default, the Bode 100 makes use of dBm because the output stage unit. 1 dBm equals 1 mW at 50 Ω load. “Vpp” could be chosen to show the output voltage in peak-to-peak voltage. Notice that the interior supply voltage is 2 instances larger than the displayed worth and legitimate when a 50 Ω load is related to the output.
- Attenuator: Set the enter attenuators 20 dB for Receiver 1 (Channel 1) and 0 dB for Receiver 2 (Channel 2).
- Receiver bandwidth: Choose the receiver bandwidth used for the measurement. Greater receiver bandwidth will increase the measurement pace. Cut back the receiver bandwidth to cut back noise and to catch narrow-band resonances.
Determine 6 The above diagram reveals {hardware} setup in Achieve/Section Measurement mode and measurement configuration. Supply: Renesas
Earlier than beginning the measurement, the Bode 100 must be calibrated. It will make sure the accuracy of the measurements. Press the “Full Vary Calibration” button as proven in Determine 7. To realize most accuracy, don’t change the attenuators after exterior calibration is carried out.
Determine 7 Press the “Full Vary Calibration” button to make sure measurement accuracy. Supply: Renesas
Determine 8 Right here is how Full Vary Calibration Window seems to be like. Supply: Renesas
Join OUTPUT, CH1, and CH2 as proven under and carry out the calibration by urgent the Begin button.
Determine 9 In calibration setup, Join OUTPUT, CH1 and CH2, and press the Begin button. Supply: Renesas
Determine 10 That is how carried out Calibration Window seems to be like. Supply: Renesas
For all LDOs:
- The enter capacitor will filter out a few of the indicators injected into the LDO, so it’s greatest to take away the enter capacitors for the examined LDO or preserve one as small as potential.
- Configure the community analyzer; use the facility provide to energy the road injector and join the output of the community analyzer to the open sound management (OSC) enter of the road injector.
- Energy up the system below check (DUT) and configure the examined LDO’s output voltage. To forestall harm to the PMIC, the LDO’s enter voltage ought to be lower than or equal to the max enter voltage. It’s extremely really helpful to energy up the LDO with no resistive load, then apply the load and alter the enter voltage.
- Configure the LDO VOUT as laid out in Desk 2.
- Allow the LDO below check and use a voltmeter to verify the output voltage.
- To make sure that the start-up present restrict doesn’t forestall the LDO from beginning accurately, join the resistive load to the LDO as soon as the VOUT voltage has reached its max stage.
- Alter the voltage on the J2120A OUT terminals to their goal VIN.
- Join the primary channel (CH1) of the community analyzer to the enter of the LDO below check utilizing a brief coaxial cable.
- Join the second channel (CH2) of the community analyzer to the output of the LDO below check utilizing a brief coaxial cable.
- Monitor the output voltage of the road injector on an oscilloscope. Carry out a frequency sweep and verify that the minimal enter voltage and an applicable peak to peak stage for check are achieved. Guarantee that the AC element is 200 mVpp or decrease.
Determine 11 This simplified instance reveals headroom influence on the ripple magnitude. Supply: Renesas
Notice that headroom for the PSRR shouldn’t be the identical because the dropout voltage parameter (Vdo) specified within the datasheets (see Determine 11). Headroom within the context of PSRR refers back to the further voltage margin above the output voltage that an LDO requires to successfully reject variations within the enter voltage.
Primarily, it ensures that the LDO can preserve a secure output regardless of fluctuations within the enter energy provide. Dropout voltage (Vdo), however, is a selected parameter outlined within the datasheets of LDOs.
It’s the minimal distinction between the enter voltage (VIN) and the output voltage (VOUT) at which the LDO can nonetheless regulate the output voltage accurately below static DC circumstances. When the enter voltage drops under this minimal threshold, the LDO can now not preserve the desired output voltage, resulting in potential efficiency points.
Determine 12 Instance highlights utilized ripple and its magnitude with DC offset for LDO’s enter. Supply: Renesas
- Arrange the community analyzer through the use of cursors to measure the PSRR at every required frequency (1 kHz, 100 kHz and 1 MHz). Add extra cursors if wanted to measure peaks as proven in Determine 13.
Determine 13 That is how design engineers can work with cursors. Supply: Renesas
- Seize photographs for every measured situation.
Determine 14 Instance reveals captured PSRR graph for the SLG51003 LDO. Supply: Renesas
Determine 15 Bench measurement setup is proven for the SLG51003 PSRR.
Clear and exact PSRR measurement
This system gives a transparent and exact strategy for measuring the PSRR for the SLG5100X household of PMICs utilizing the Omicron Lab Bode 100 and Picotest J2120A. Correct PSRR measurements within the 10 Hz to 10 MHz frequency vary are essential for validating LDO efficiency and making certain strong energy administration.
The accompanying figures function a priceless reference for setup and interpretation, whereas strict adherence to those pointers enhances measurement reliability. By following this framework, engineers can obtain high-quality PSRR assessments, finally contributing to extra environment friendly and dependable energy administration options.
Oleh Yakymchuk is functions engineer at Renesas Electronics’ workplace in Lviv, Ukraine.
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