ADP7157ARDZ

The ADP7157ARDZ is an adjustable output low-dropout linear regulator from Analog Devices that combines high output current capability (1.2A) with ultralow noise and high power supply rejection ratio (PSRR). Designed using an advanced proprietary architecture, this LDO delivers industry-leading noise and PSRR performance while requiring only a small 10 microfarad ceramic output capacitor for stability, significantly reducing solution size and cost compared to competing high-current low-noise LDOs. The output voltage is adjustable from 1.2V to 3.3V through an external resistor divider connected to the REF_SENSE pin. The internal 1.2V bandgap reference is buffered and available on the REF pin for additional noise filtering through an external bypass capacitor, which further reduces output noise to the exceptional 0.9 microvolt rms level (100 Hz to 100 kHz). A unique VOUT_SENSE pin allows remote sensing directly at the load, compensating for voltage drops in PCB traces and ensuring accurate voltage regulation at the point of use. The precision enable input allows the device to be turned on/off with an accurately defined threshold voltage, enabling accurate power supply sequencing in multi-rail systems. The ADP7157 is available in two package options: a compact 10-lead 3x3mm LFCSP for space-constrained applications, and an 8-lead SOIC for designs preferring traditional surface-mount packages. The ADP7157ARDZ specifically is the 8-lead SOIC version. Both versions include comprehensive protection features including current limiting and thermal shutdown. With its combination of low noise, high PSRR, high current, and wide input voltage range, the ADP7157 is ideal for powering noise-sensitive circuits such as high-speed SerDes, FPGA and ASIC core supplies, RF and PLL circuits, high-speed data converters, and precision analog circuitry in test/measurement, medical, telecommunications, and industrial applications. The device is supported by ADIsimPower, ADI online power design tool that simplifies component selection and simulation.

The ADP7157 is a low-dropout linear regulator that uses a proprietary architecture to achieve exceptionally high PSRR and low output noise performance. At its core, the device consists of a bandgap reference, an error amplifier, a pass element (PMOS transistor), and a feedback network. The reference voltage is generated by an on-chip bandgap circuit that produces a precise 1.2V voltage with low temperature coefficient. This reference is buffered and made available on the REF pin, which can be bypassed with an external capacitor to further reduce reference noise – this is one of the key techniques that enables the ultralow noise performance of the ADP7157. The error amplifier compares the reference voltage with a divided-down sample of the output voltage and drives the gate of the PMOS pass transistor to maintain a constant output voltage. The output voltage is set by the external resistor divider connected to the REF_SENSE pin according to the formula VOUT = VREF x (R1 + R2) / R2, where R1 is the resistor from VOUT to REF_SENSE and R2 is from REF_SENSE to ground. The VOUT_SENSE pin provides Kelvin sensing capability: it is internally connected to VOUT through a small resistor and is intended to be connected directly to the load point. This eliminates the voltage drop caused by load current flowing through PCB trace resistance, ensuring that the regulated voltage is accurate at the actual point of use. The proprietary architecture of the ADP7157 provides high PSRR across a wide frequency range. At low frequencies (up to several kHz), the high DC gain of the error amplifier provides excellent line regulation and PSRR. At mid-frequencies (1 kHz to 100 kHz), the carefully designed compensation network and low-impedance pass element maintain 82 dB PSRR. At high frequencies (up to 1 MHz), the output capacitor and the low output impedance of the pass element provide 55 dB PSRR, which is significantly better than typical LDOs at these frequencies. The device also includes a precision enable circuit with an accurate voltage threshold for power sequencing, thermal shutdown protection at approximately 150C junction temperature, and current limiting to protect the pass element from overload conditions.

• Powering high-speed SerDes transceivers in telecom and data center equipment
• FPGA, ASIC, and processor core and I/O power supply rails
• Low-noise VCO and PLL power supplies in RF and communication systems
• High-speed ADC and DAC analog supply and reference rails
• Precision analog front-end circuits for instrumentation
• Medical imaging and patient monitoring equipment power
• Test and measurement: oscilloscopes, spectrum analyzers, signal generators
• Post-regulation after switching power supplies for noise-sensitive loads
• Industrial control and automation signal processing circuits
• Laboratory and scientific instrumentation