onsemi BAT54

Overview

The onsemi BAT54 is a single low-barrier Schottky diode designed for high-speed switching, signal steering, voltage clamping, and circuit protection. Its 30 V reverse-voltage rating, 200 mA forward-current capability, low current-dependent forward voltage, and 5 ns maximum reverse-recovery time make it suitable for compact low-voltage analog and digital circuits.

For engineers reviewing the BAT54 datasheet, BAT54 pinout, BAT54 application, or BAT54 equivalent, it is important to distinguish the original legacy BAT54 from the current BAT54LT1G continuation. The original BAT54 is an obsolete SOT-23 device historically associated with Fairchild Semiconductor and now supported under onsemi product heritage, while BAT54LT1G is the appropriate onsemi replacement for new production designs.

Technical Context

The BAT54 forward voltage depends strongly on operating current. Maximum specified values progress from 0.24 V at 0.1 mA to 0.80 V at 100 mA, so a single generic "low forward voltage" value should not be used across the entire load range. Designers should calculate conduction loss and available voltage headroom at the circuit's actual forward current.

As with other Schottky diodes, BAT54 reverse leakage increases substantially with junction temperature. The 2 µA maximum leakage specification applies at 25 V reverse bias under the stated test condition and should not be interpreted as a high-temperature limit. Pin 2 is internally unconnected and must not be treated as a duplicate anode or cathode connection.

Key Specifications

Pinout & Package

The BAT54 uses a three-lead SOT-23 package with a single diode between pins 1 and 3. PCB footprints should preserve the correct anode-to-cathode orientation and should not infer connectivity from dual-diode BAT54A, BAT54C, or BAT54S variants, which have different internal arrangements.

Key Features

• Single 30 V, 200 mA Schottky barrier diode
• Low forward voltage for reduced signal loss and clamp threshold
• 5 ns maximum reverse-recovery time for fast switching
• 10 pF maximum capacitance at 1 V and 1 MHz
• Compact three-lead SOT-23 surface-mount package
• −55°C to +150°C junction-temperature range
• Suitable for switching, voltage clamping, signal steering, and circuit protection
• Direct current-design migration path to onsemi BAT54LT1G

Applications

Equivalent & Alternatives

Quality

Quality control for legacy BAT54 inventory should include manufacturer traceability, lot-code review, SOT-23 dimensional inspection, marking verification, solderability assessment, and electrical sampling for forward voltage and reverse leakage. Original BAT54 devices may carry the legacy L4P marking, while BAT54LT1G uses JV3; marking differences should be evaluated together with packaging and traceability records rather than used as the sole authenticity criterion.

Because Schottky leakage is temperature-sensitive, applications involving high-impedance or precision nodes should qualify samples at the actual reverse voltage and maximum operating temperature. Assembly controls should also protect the small SOT-23 package from excessive reflow exposure, moisture damage, contamination, and mechanical stress.

Availability

The original onsemi BAT54 is obsolete and is generally encountered as legacy inventory rather than ongoing factory production. BAT54 may be available at Aetrix Electronics for maintenance, repair, and existing-production requirements, subject to lot availability and traceability review. For new designs or long-term supply planning, onsemi BAT54LT1G should be evaluated as the preferred replacement.

Manufacturer

BAT54 is associated with the Fairchild Semiconductor small-signal diode portfolio now maintained under onsemi product heritage. onsemi supplies semiconductor solutions for power management, sensing, protection, automotive systems, industrial electronics, communications, and consumer applications. Engineers should distinguish the discontinued bare BAT54 designation from currently supported onsemi variants such as BAT54LT1G and automotive-qualified NSVBAT54LT1G.

FAQ

What type of diode is the onsemi BAT54?

The onsemi BAT54 is a single Schottky barrier diode intended for high-speed switching, voltage clamping, signal steering, and low-current protection. BAT54 combines a 30 V reverse-voltage rating with 200 mA forward-current capability in a compact SOT-23 package.

What are the maximum voltage and current ratings of BAT54?

BAT54 is rated for a maximum reverse voltage of 30 V and a maximum continuous forward current of 200 mA. BAT54 also supports short non-repetitive forward-current surges up to 600 mA, but allowable pulse energy remains limited by junction temperature and package power dissipation.

What forward voltage should be expected from BAT54?

BAT54 forward voltage varies with current rather than remaining at one fixed value. Maximum limits are 0.24 V at 0.1 mA, 0.32 V at 1 mA, 0.40 V at 10 mA, 0.50 V at 30 mA, and 0.80 V at 100 mA, so BAT54 conduction loss must be calculated at the intended operating current.

What is the correct BAT54 pinout?

In the three-lead SOT-23 package, BAT54 pin 1 is the anode, pin 2 is not connected, and pin 3 is the cathode. BAT54 should not be assigned the pinout of BAT54A, BAT54C, or BAT54S because those related devices contain different dual-diode configurations.

Is BAT54 suitable for high-speed or high-impedance signals?

BAT54 has a 5 ns maximum reverse-recovery time and is suitable for many fast signal-steering and clamping circuits. However, BAT54 has up to 10 pF total capacitance and reverse leakage that increases with temperature, so bandwidth and leakage errors must be checked in high-frequency or high-impedance applications.

What is the difference between BAT54 and BAT54LT1G?

The original BAT54 is an obsolete legacy device, while BAT54LT1G is the current onsemi continuation for the same basic single-diode SOT-23 function. BAT54 carried a legacy 290 mW power-dissipation rating and L4P marking, whereas BAT54LT1G specifies 200 mW and uses the JV3 marking, so thermal margin and identification should be reviewed during migration.

What is the recommended replacement for an obsolete BAT54?

For most non-automotive designs, onsemi BAT54LT1G is the preferred replacement for BAT54. NSVBAT54LT1G is the corresponding option when AEC-Q101 qualification and PPAP capability are required, while cross-manufacturer BAT54 equivalents should be approved only after pinout, forward voltage, leakage, capacitance, thermal limits, and packaging have been compared.