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August 22, 2022

ES9311Q Dual, Ultra-Low Noise Linear Regulator

ESS TECHNOLOGY, INC. 109 Bonaventura Dr., San Jose, CA 95134, USA. Tel (408) 643-

8800 • WWW.ESSTECH.COM

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FUNCTIONAL DESCRIPTION

The ES9311 is a dual, ultra-low noise voltage, low dropout (LDO) regulator designed for applications that require two stable

voltage outputs that can supply up to 150mA per channel. Output voltage noise is typically <1µVrms from 100Hz to 100kHz

and excellent power supply rejection of 90dB from 100Hz to 25kHz make this dual reference ideal for audio data converters

and PLL supplies. The voltage reference design combines the advantages of both series voltage and shunt voltage

references in one. That means the design has a low quiescent current, as in the series voltage reference, combined with a

low output impedance that is characteristic of the shunt voltage reference. The output impedance is low over the whole

output current range. In addition, the circuit is designed to operate with no output decoupling capacitor hence reducing BOM

cost and PCB area. High-performance regulator features such as, soft-start, under-voltage lockout, fast transient response,

over-temperature shutdown, over-current protection, and power-good indicators are included for ease-of-use and device

protection.

Dual Regulator Functional Blocks

The dual LDO regulator consists of: a low-noise bandgap reference with fast charge for the filter capacitor, reference buffer

amplifier, two high-performance 150mA low-dropout regulators, protection circuitry against fault conditions, plus control logic

and signaling. There are five Enable inputs, one for each regulated supply, plus ones for enabling soft-start, over-

temperature protection, and quick-discharge of the output voltage. All the Enable inputs include Schmitt triggers to prevent

signal

“chatter” when the input is noisy. There are four, active-low status outputs: power-good1, power-good2, over-

temperature warning, and over-temperature shutdown. Power-good signals are activated when the input voltage is above

3.0V and when the output exceeds 90% of final value. If any overload condition occurs, e.g. over-current or over-

temperature, the power-good signal will disappear. The regulator outputs use Kelvin sensing, i.e. force and sense

connections, to maximize the voltage accuracy and minimize voltage perturbations right at the DAC AVCC connections.

Input Supply

The E9311 operates from a single +3.5V to +5.5V supply and provides two outputs each capable of providing up to 150mA.

Power Supply Rejection (PSR) is typically 90dB that extends beyond the audio frequency range, up to 25kHz. When

powering the ES9311 from a switching power supply it is advisable to employ HF decoupling on the input to minimize noise

that may mix down into the audio band. High frequency PSR can also be improved by increasing the value of the noise

filtering capacitors from 1µF to 10µF and this is recommended for Audio DAC and ADC applications.

The ES9311 includes an Under-Voltage Lockout (UVLO) circuit that ensures the output voltage rises gracefully without

glitches or false starts that might introduce audible clicks or noise.

Outputs & Remote Sensing

Output noise from each supply is typically under 1µVrms from 100Hz to 100kHz, and less than 1.3µVrms from 10Hz to

100kHz. The temperature coefficient of each output is typically 50ppm/°C with a drift of ±0.5% over temperature which

corresponds to a DAC gain drift of ±0.05dB over temperature. Line and load regulation are typically 0.7mV/V and 16mV/A

(16mΩ output resistance) respectively. Isolation between the two outputs, which might affect crosstalk between left and right

channels, is over 120dB at 1kHz so the effect is negligible.

Remote sensing maintains an accurate voltage at the load, even at high load currents, despite voltage drops in the

connecting copper track. Bench power supply remote sensing uses a 4-wire connection, or Kelvin connection, that separates

the current path to and from the load from the voltage signal developed across the load. The 4-wire measurement bypasses

the voltage drop in the connecting cables by providing a voltage signal that is fed back to high-impedance ground and output

sense inputs. Slightly different from a bench power supply, the ES9311 dual regulator relies on a low-impedance ground

plane for the current return path and only uses remote sensing for the output connections as these tracks drop the most

voltage. This 3-wire scheme maximizes load regulation in conjunction with a low-impedance ground plane.

Output Noise Reduction

The ES9311 requires three 1µF noise filter capacitors, CRF, CF1, and CF2 to achieve its low-noise performance. These

capacitors should be low-leakage ceramic types with low-ESR and temperature rated for operation up to the maximum

internal operating temperature of the end product. Dielectric types X7R or X5R are highly recommended for these

capacitors. Higher values of noise filter capacitor can be used to increase high frequency PSR, e.g. 10µF, and this value and

is recommended for the highest performance Audio applications. A fast-charge circuit that rapidly charges the noise bypass

capacitor CRF minimizes startup time.