Nexperia USA Inc. PSSI2021SAY,115

Overview

PSSI2021SAY,115 from Nexperia is a resistor-equipped PNP transistor with integrated diodes forming a monolithic constant current source in SOT353 (SC-88A) package. It delivers stabilized output current from 15 µA to 50 mA via external resistor biasing, operates up to 75 V supply, and serves as a compact LED driver or active bias controller in automotive and audio systems.

For engineers reviewing the PSSI2021SAY,115 datasheet, PSSI2021SAY,115 pinout, PSSI2021SAY,115 application, or PSSI2021SAY,115 equivalent, key selection criteria include output current adjustability via R_EXT, thermal resistance of 370 K/W, junction temperature rating of 150 °C, and compatibility with FR4 PCB mounting under industrial ambient conditions.

Technical Context

This device integrates a PNP transistor, two diodes, and an internal ~48 kΩ resistor on a single die to form a self-biasing constant current sink. Current regulation relies on external resistor connection between pins 4 (REXT) and 5 (VS), enabling precise I_OUT setting across load voltages up to 73 V.

It exhibits ±0.5% load stability over V_OUT = 1–10 V at 12 V supply and 0.15 %/K temperature coefficient for I_OUT over −55 °C to +150 °C ambient range. Supply current scales from 240 µA (at 12 V, 15 µA I_OUT) to 2.2 mA (at 75 V, same I_OUT).

Key Specifications

Pinout & Package

SOT353 (SC-88A) plastic surface-mounted package: 5-lead, 1.35 mm × 1.15 mm footprint, 0.65 mm pitch, 0.45 mm max height. Designed for high-density routing and reflow-compatible assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar constant current source applications.

Compared with NSI45020AZT1G and AP2125K-1.8TRG1, PSSI2021SAY,115 uniquely offers externally adjustable current sinking up to 50 mA with 75 V supply capability and SOT353 space efficiency - making it the only viable option for tunable, high-voltage, low-footprint constant current needs.

Availability

PSSI2021SAY,115 is available at Aetrix Electronics and suitable for automotive lighting systems, industrial sensor excitation circuits, audio amplifier bias networks, and precision voltage reference designs requiring stable component supply and long-term lifecycle continuity.

Supply support for PSSI2021SAY,115 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Nexperia is a global leader in discrete, logic, and PowerMOS semiconductors, spun off from NXP in 2017 and focused on automotive, industrial, computing, and consumer markets.

PSSI2021SAY belongs to Nexperia's resistor-equipped transistor (RET) product line, engineered to replace discrete bias networks with monolithic, thermally stable current sources for LED driving and analog signal conditioning.

FAQ

What is the minimum external resistor value needed to achieve 50 mA output current?

Using the formula I_OUT ≈ 0.617/R_EXT + 15 µA, solving for R_EXT at I_OUT = 50 mA yields ~12.3 Ω. However, practical minimum is constrained by power dissipation in R_EXT and internal device limits. Nexperia recommends ≥100 Ω for reliability and thermal margin in continuous operation.

Can PSSI2021SAY,115 be used in high-side current sensing configurations?

No - PSSI2021SAY,115 is a current sink (low-side configuration). Its IOUT pin is the collector-emitter current path referenced to GND. For high-side sensing, a dedicated current-sense amplifier or high-side switch with integrated sense is required; this device lacks voltage-sense terminals or bidirectional capability.

Does the device require a heatsink for 20 mA operation at 70 °C ambient?

No. At 20 mA and 70 °C ambient, power dissipation is ~1.4 W × (73 V – 2 V) ≈ 1.4 mW (worst-case V_OUT = 73 V), well below the 335 mW P_TOT limit. With R_TH(j-a) = 370 K/W, junction rise is <0.5 °C - no heatsink or copper pour is necessary for this condition.

Is pin 1 (n.c.) electrically isolated or internally tied to substrate?

Pin 1 is confirmed as unconnected - no internal bond wire or die attachment. It is electrically isolated from all active circuitry and may be left floating or grounded per PCB ESD strategy, but grounding is not required for functional operation or thermal performance.