Methods to measure PSRR of PMICs

Making certain steady energy administration is essential in fashionable electronics, and the ability 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 skill 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 techniques that preserve constant operation even underneath various energy circumstances.

Determine 1 Right here is the final methodology to measure PSRR. Supply: Renesas

PSRR is a crucial parameter that assesses an LDO’s functionality to take care of a constant output voltage amidst variations within the enter energy provide. Reaching excessive PSRR is essential in eventualities by which the enter energy provide experiences fluctuations, thereby making certain the dependability of the output voltage. Determine 1 under illustrates the final methodology for measuring PSRR.

The mathematical expression to calculate the PSRR worth is:

PSRR = 20 log₁₀ V_IN/V_OUT

The place V_IN and V_OUT 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 take a look at atmosphere with precision. The next design outlines using the listed tools to determine a sturdy and dependable take a look at configuration.

First, join the ability 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 steady DC voltage whereas the AC ripple part is supplied 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 likely to be 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 certain 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 document and analyze the measurements. This information can be utilized to compute the PSRR values and consider the PMIC’s skill to take care of a steady 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 techniques.

Desk 1: Right here is a top level view of the devices utilized in PSRR measurements. Supply: Renesas

Desk 2 See the take a look at 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 the right way to set Hint 1. Supply: Renesas

To get the goal PSRR measurement, select the next settings within the “{Hardware} Setup”:

1. Frequency: Change the Begin frequency to “10 Hz” and Cease frequency to “10 MHz”.
2. Supply mode: Select between Auto off or All the time on. In Auto off mode, the supply will probably be mechanically turned off every time it’s not used (when a measurement is stopped). In All the time 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.
3. Supply stage: Set the fixed supply stage to “-16 dB” or increased for the output stage. The unit may 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” may be chosen to show the output voltage in peak-to-peak voltage. Notice that the inner supply voltage is 2 instances increased than the displayed worth and legitimate when a 50 Ω load is related to the output.
4. Attenuator: Set the enter attenuators 20 dB for Receiver 1 (Channel 1) and 0 dB for Receiver 2 (Channel 2).
5. Receiver bandwidth: Choose the receiver bandwidth used for the measurement. Larger 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. This can make sure the accuracy of the measurements. Press the “Full Vary Calibration” button as proven in Determine 7. To attain 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 appears 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 appears like. Supply: Renesas

For all LDOs:

1. 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 hold one as small as attainable.
2. Configure the community analyzer; use the ability 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.
3. Energy up the gadget underneath take a look at (DUT) and configure the examined LDO’s output voltage. To stop injury to the PMIC, the LDO’s enter voltage ought to be lower than or equal to the max enter voltage. It’s extremely really useful to energy up the LDO with out a resistive load, then apply the load and regulate the enter voltage.
4. Configure the LDO V_OUT as laid out in Desk 2.
5. Allow the LDO underneath take a look at and use a voltmeter to examine the output voltage.
6. 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 V_OUT voltage has reached its max stage.
7. Modify the voltage on the J2120A OUT terminals to their goal V_IN.
8. Join the primary channel (CH1) of the community analyzer to the enter of the LDO underneath take a look at utilizing a brief coaxial cable.
9. Join the second channel (CH2) of the community analyzer to the output of the LDO underneath take a look at utilizing a brief coaxial cable.
10. Monitor the output voltage of the road injector on an oscilloscope. Carry out a frequency sweep and examine that the minimal enter voltage and an acceptable peak to peak stage for take a look at are achieved. Ensure that the AC part is 200 mVpp or decrease.

Determine 11 This simplified instance reveals headroom affect on the ripple magnitude. Supply: Renesas

Notice that headroom for the PSRR just isn’t 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 extra 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 steady output regardless of fluctuations within the enter energy provide. Dropout voltage (Vdo), alternatively, is a particular parameter outlined within the datasheets of LDOs.

It’s the minimal distinction between the enter voltage (V_IN) and the output voltage (V_OUT) at which the LDO can nonetheless regulate the output voltage accurately underneath static DC circumstances. When the enter voltage drops under this minimal threshold, the LDO can now not preserve the required 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

11. Arrange the community analyzer by utilizing 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

12. Seize photos 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 technique supplies 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 tips enhances measurement reliability. By following this framework, engineers can obtain high-quality PSRR assessments, in the end contributing to extra environment friendly and dependable energy administration options.

Oleh Yakymchuk is purposes engineer at Renesas Electronics’ workplace in Lviv, Ukraine.

Associated Content material

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• Energy Provide Ripple Rejection and Linear Regulators: What’s all of the noise about?
• Designing with a whole simulation take a look at bench for op amps: Enter-referred errors
• Perceive how PSRR and different power-supply components have an effect on mobile-phone audio high quality

The submit Methods to measure PSRR of PMICs appeared first on EDN.

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