DS1721S Equivalent & Substitute Parts

Part Overview

The DS1721S is a digital temperature sensor manufactured by Analog Devices Inc./Maxim Integrated, designed for local temperature measurement across the -55°C to 125°C range. This component operates via I2C interface with 11-bit resolution and is housed in an 8-SOIC surface mount package. The DS1721S is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. Substitute parts must maintain functional compatibility while meeting current RoHS and compliance standards.

Key Parameters

Parameter	DS1721S
Sensor Type	Digital, Local
Temperature Range (Local)	-55°C ~ 125°C
Output Type	I2C
Supply Voltage	2.7V ~ 5.5V
Resolution	11 bits
Accuracy (Highest/Lowest)	±1°C / ±2°C
Package	8-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution for the DS1721S is determined by the following critical parameters:

Primary Compatibility Criteria:

Temperature sensing range: -55°C ~ 125°C minimum
Digital output interface: I2C or I2C/SMBus compatible
Resolution: 11-bit preferred for functional equivalence
Package: 8-SOIC form factor
Supply voltage: 2.7V ~ 5.5V compatibility
Mounting: Surface mount

Substitution Categories:

Direct Equivalents (DS1721S+ variants): Identical electrical and mechanical specifications with improved product status and RoHS3 compliance. These are pin-compatible replacements with the same base product number DS1721.

Functional Upgrades (Texas Instruments TMP series): Parts meeting the core temperature range, I2C/SMBus interface, and 8-SOIC package. These offer improved accuracy, active product status, and RoHS3 compliance. Resolution varies (9-bit or 11-bit) and temperature operating ranges differ slightly.

Manufacturer Recommended Alternative (Microchip AT30TS74-SS8M-B): Meets extended temperature range (-55°C ~ 125°C), 11-bit resolution, and I2C/SMBus interface with active product status and RoHS3 compliance. Lower minimum supply voltage (1.7V) provides additional design flexibility.

Parameter Comparison

Part Number	Manufacturer	Temperature Range	Resolution	Output Type	Supply Voltage	Accuracy (Highest)	Package	Product Status	RoHS Status
DS1721S	Analog Devices/Maxim	-55°C ~ 125°C	11 b	I2C	2.7V ~ 5.5V	±1°C	8-SOIC	Obsolete	Non-compliant
DS1721S+	Analog Devices/Maxim	-55°C ~ 125°C	11 b	I2C	2.7V ~ 5.5V	±1°C	8-SOIC	Active	ROHS3 Compliant
DS1721S+T&R	Analog Devices/Maxim	-55°C ~ 125°C	11 b	I2C	2.7V ~ 5.5V	±1°C	8-SOIC	Active	ROHS3 Compliant
TMP175AID	Texas Instruments	-40°C ~ 125°C	9 b	I2C/SMBus	2.7V ~ 5.5V	±1.5°C	8-SOIC	Obsolete	ROHS3 Compliant
TMP175AIDR	Texas Instruments	-40°C ~ 125°C	9 b	I2C/SMBus	2.7V ~ 5.5V	±1.5°C	8-SOIC	Active	ROHS3 Compliant
TMP275AID	Texas Instruments	-40°C ~ 125°C	11 b	SMBus	2.7V ~ 5.5V	±0.5°C	8-SOIC	Obsolete	ROHS3 Compliant
TMP275AIDR	Texas Instruments	-40°C ~ 125°C	11 b	SMBus	2.7V ~ 5.5V	±0.5°C	8-SOIC	Active	ROHS3 Compliant
TMP75AID	Texas Instruments	-40°C ~ 125°C	11 b	I2C/SMBus	2.7V ~ 5.5V	±2°C	8-SOIC	Obsolete	ROHS3 Compliant
TMP75AIDR	Texas Instruments	-40°C ~ 125°C	11 b	I2C/SMBus	2.7V ~ 5.5V	±2°C	8-SOIC	Active	ROHS3 Compliant
TMP75AIDRG4	Texas Instruments	-40°C ~ 125°C	11 b	I2C/SMBus	2.7V ~ 5.5V	±2°C	8-SOIC	Obsolete	ROHS3 Compliant
AT30TS74-SS8M-B	Microchip Technology	-55°C ~ 125°C	11 b	I2C/SMBus	1.7V ~ 5.5V	±2°C	8-SOIC	Active	ROHS3 Compliant

Engineering Selection Recommendations

Preferred Direct Replacement: DS1721S+ or DS1721S+T&R are the optimal choices for direct substitution. Both maintain identical electrical specifications and package form factor as the original DS1721S while offering active product status and ROHS3 compliance. The primary difference is packaging: DS1721S+ is supplied in tube format, while DS1721S+T&R is supplied in cut tape with Digi-Reel format. Selection depends on assembly process requirements.

Alternative for Extended Production Life: TMP75AIDR (Texas Instruments) provides an active product with 11-bit resolution, I2C/SMBus interface compatibility, and ROHS3 compliance. The temperature operating range is -40°C ~ 125°C, which covers the DS1721S range above -40°C. This part is suitable for applications not requiring the full -55°C lower limit. Accuracy specification is ±2°C at the highest, matching the DS1721S lower accuracy specification.

Highest Accuracy Alternative: TMP275AIDR (Texas Instruments) offers superior accuracy (±0.5°C highest) with 11-bit resolution and active product status. However, the temperature range is limited to -40°C ~ 125°C and the output interface is SMBus only (not I2C). This part requires protocol compatibility verification before selection.

Manufacturer Recommended Option: AT30TS74-SS8M-B (Microchip Technology) matches the full -55°C ~ 125°C temperature range with 11-bit resolution and active product status. The lower minimum supply voltage (1.7V) provides additional design margin. I2C/SMBus interface compatibility ensures protocol flexibility. This part is suitable for new designs requiring extended temperature coverage and long-term availability.

Frequently Asked Questions (FAQ)

Q: Can DS1721S+ be used as a direct replacement for DS1721S? A: Yes. DS1721S+ is electrically and mechanically identical to DS1721S with identical pin configuration, temperature range, resolution, and I2C interface. The primary advantage is active product status and ROHS3 compliance. Packaging format differs (tube vs. cut tape), which may affect assembly process compatibility.

Q: What is the key difference between DS1721S+T&R and DS1721S+? A: Both parts are electrically identical. DS1721S+T&R is supplied in cut tape with Digi-Reel packaging, while DS1721S+ is supplied in tube format. Selection depends on assembly equipment compatibility and tape-and-reel handling capabilities.

Q: Why do Texas Instruments TMP series parts have a narrower temperature range? A: TMP175 and TMP75 series parts operate from -40°C minimum, not -55°C. Applications requiring the full -55°C lower limit must use DS1721S+, DS1721S+T&R, or AT30TS74-SS8M-B. TMP275 series also operates from -40°C minimum.

Q: Is TMP275AIDR a suitable replacement despite SMBus-only interface? A: TMP275AIDR offers superior accuracy (±0.5°C) but operates only to -40°C minimum and uses SMBus interface exclusively. Replacement is suitable only if the application protocol stack supports SMBus and does not require -55°C operation.

Q: What is the advantage of AT30TS74-SS8M-B over other alternatives? A: AT30TS74-SS8M-B maintains the full -55°C ~ 125°C temperature range with 11-bit resolution and active product status. The lower minimum supply voltage (1.7V vs. 2.7V) provides additional design flexibility. I2C/SMBus interface compatibility ensures protocol flexibility for existing designs.

Q: Are all substitute parts ROHS3 compliant? A: All substitute parts listed are ROHS3 compliant. The original DS1721S is RoHS non-compliant. Compliance verification is required for applications subject to RoHS regulations.

Q: Can I use TMP175AIDR if my application only operates above -40°C? A: Yes, if the application temperature range is -40°C ~ 125°C or narrower. TMP175AIDR provides active product status and ROHS3 compliance. However, resolution is 9-bit compared to DS1721S 11-bit resolution, which may affect measurement precision in applications requiring finer temperature granularity.

Q: What packaging options are available for substitute parts? A: DS1721S+ is available in tube format. DS1721S+T&R is available in cut tape with Digi-Reel. TMP series parts are available in tube or cut tape with Digi-Reel formats depending on specific part number suffix. AT30TS74-SS8M-B is available in tube format. Verify packaging compatibility with assembly equipment before final selection.

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