STT4PF20V P-Channel MOSFET Equivalent & Substitute Parts

Part Overview

The STT4PF20V is a P-Channel MOSFET manufactured by STMicroelectronics in the STripFET™ II series. This device is rated for 20V drain-to-source voltage with 3A continuous drain current in a surface mount SOT-23-6 package. The part is currently classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. Substitute parts must maintain electrical compatibility across voltage ratings, current handling, and thermal characteristics while accommodating package variations.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	20	V
Continuous Drain Current (Id) @ 25°C	3	A
On-Resistance (Rds On) @ 4.5V	110	mOhm
Gate Threshold Voltage (Vgs(th))	600	mV
Power Dissipation (Max)	1.6	W
Operating Temperature (TJ)	150	°C
Package Type	SOT-23-6	—
FET Type	P-Channel	—
Technology	MOSFET (Metal Oxide)	—

Substitute Part Grouping Explanation

Substitute parts for the STT4PF20V are selected based on the following critical parameters:

Primary Substitution Criteria:

FET Type: P-Channel (required)
Drain to Source Voltage (Vdss): 20V minimum (allows higher ratings)
Continuous Drain Current (Id): 3A minimum at 25°C (allows higher ratings)
Package Type: SOT-23-6 or compatible thin-profile variants (SOT-23-6 Thin, TSOT-23-6)
Mounting Type: Surface Mount
Technology: MOSFET (Metal Oxide)
RoHS3 Compliance: Required
Moisture Sensitivity Level: MSL 1 (Unlimited)

Substitution Logic: Parts meeting or exceeding the voltage and current specifications are considered functionally equivalent. On-resistance (Rds On) improvements are acceptable as they reduce power dissipation and heat generation. Gate threshold voltage variations within the specified range do not prevent substitution. Package compatibility includes SOT-23-6 standard and thin-profile variants that maintain the same pinout and thermal characteristics.

Parameter Comparison

Parameter	STT4PF20V (Main)	FDC634P	FDC640P	FDC642P	ZXMP3A17E6TA
Manufacturer	STMicroelectronics	onsemi	onsemi	onsemi	Diodes Incorporated
Product Status	Obsolete	Active	Active	Active	Active
FET Type	P-Channel	P-Channel	P-Channel	P-Channel	P-Channel
Vdss (V)	20	20	20	20	30
Id @ 25°C (A)	3	3.5	4.5	4	3.2
Rds On @ 4.5V (mOhm)	110	80	53	65	70
Vgs(th) @ 250µA (V)	0.6	1.5	1.5	1.5	1
Gate Charge @ 4.5V (nC)	7.8	10	13	16	15.8
Power Dissipation (W)	1.6	1.6	1.6	1.6	1.1
Operating Temperature (°C)	150	-55 to 150	-55 to 150	-55 to 150	-55 to 150
Package	SOT-23-6	SOT-23-6 Thin, TSOT-23-6	SOT-23-6 Thin, TSOT-23-6	SOT-23-6 Thin, TSOT-23-6	SOT-23-6
RoHS3 Compliant	Yes	Yes	Yes	Yes	Yes
MSL Rating	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)

Engineering Selection Recommendations

FDC634P (onsemi PowerTrench®) The FDC634P is an active production part with 3.5A continuous drain current, exceeding the STT4PF20V specification by 0.5A. The 20V Vdss rating matches exactly. On-resistance is reduced to 80mOhm, providing improved thermal performance. This part is suitable for direct replacement in applications where the higher current capability and lower on-resistance do not create design conflicts. RoHS3 compliance and MSL 1 rating are maintained.

FDC640P (onsemi PowerTrench®) The FDC640P offers the highest current rating at 4.5A with the lowest on-resistance at 53mOhm among all substitutes. The 20V Vdss rating is equivalent. This part provides the greatest performance margin and is recommended for applications requiring maximum thermal efficiency or where future current demands may increase. Active production status and full compliance certifications apply.

FDC642P (onsemi PowerTrench®) The FDC642P provides 4A continuous drain current with 65mOhm on-resistance, positioning it between the FDC634P and FDC640P in performance. The 20V Vdss rating is equivalent. This part offers a balanced alternative with moderate performance improvement over the original part. Active production and compliance certifications are maintained.

ZXMP3A17E6TA (Diodes Incorporated) The ZXMP3A17E6TA is rated for 30V Vdss, providing 50% higher voltage headroom than the STT4PF20V. Continuous drain current is 3.2A, slightly exceeding the original specification. On-resistance is 70mOhm at 10V gate drive. This part is suitable for applications where higher voltage margin is beneficial or where gate drive voltage differs from 4.5V. Active production status and full compliance certifications apply.

All substitute parts maintain RoHS3 compliance, MSL 1 rating, and surface mount technology. Package compatibility requires verification for thin-profile variants (SOT-23-6 Thin, TSOT-23-6) in space-constrained layouts.

Frequently Asked Questions (FAQ)

Q: Can the FDC634P, FDC640P, or FDC642P be used as direct pin-for-pin replacements for the STT4PF20V?

A: Yes. All three onsemi parts use SOT-23-6 or compatible thin-profile variants (TSOT-23-6) with identical pinout. Physical board layout compatibility requires verification for thin-profile packages, as height and footprint may differ slightly. Electrical performance is maintained across all three options.

Q: What is the primary advantage of the FDC640P over the STT4PF20V?

A: The FDC640P provides 4.5A continuous drain current (versus 3A) and 53mOhm on-resistance (versus 110mOhm). The reduced on-resistance directly lowers power dissipation and junction temperature, improving reliability and thermal margin in the application.

Q: Why does the ZXMP3A17E6TA have a 30V Vdss rating when the STT4PF20V is only 20V?

A: The ZXMP3A17E6TA is designed for higher voltage applications. The 30V rating provides additional safety margin and allows use in circuits with higher transient voltages. This part is a valid substitute for 20V applications, as it exceeds the minimum voltage requirement.

Q: Are there any thermal differences between the STT4PF20V and the substitute parts?

A: The substitute parts from onsemi (FDC634P, FDC640P, FDC642P) have lower on-resistance values, resulting in reduced power dissipation at equivalent current levels. The ZXMP3A17E6TA has a lower maximum power dissipation rating (1.1W versus 1.6W), which may affect thermal performance in high-power applications. Thermal modeling is recommended for critical designs.

Q: What is the difference between SOT-23-6 and SOT-23-6 Thin (TSOT-23-6)?

A: SOT-23-6 Thin (TSOT-23-6) is a reduced-height variant of the standard SOT-23-6 package. Both maintain identical pinout and electrical characteristics. The thin variant is used in space-constrained applications. PCB footprint compatibility must be verified before substitution.

Q: Is the STT4PF20V still available for purchase?

A: The STT4PF20V is classified as obsolete. Inventory availability is limited to existing stock. Active production alternatives (FDC634P, FDC640P, FDC642P, ZXMP3A17E6TA) are recommended for new designs and ongoing production requirements.

Q: Do all substitute parts meet the same compliance standards as the STT4PF20V?

A: Yes. All substitute parts are RoHS3 compliant, REACH unaffected, and carry MSL 1 (Unlimited) moisture sensitivity ratings. ECCN and HTSUS classifications are identical across all parts.

Q: What gate drive voltage should be used with the substitute parts?

A: The FDC634P, FDC640P, and FDC642P are optimized for 4.5V gate drive, matching the STT4PF20V specification. The ZXMP3A17E6TA is optimized for 10V gate drive. Consult device datasheets for on-resistance performance at alternative gate drive voltages.

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