Texas Instruments TMP821DR

Overview

TMP821DR from Texas Instruments is a two-phase half-wave motor predriver IC for brushless DC fan motors with push-pull winding configuration, featuring differential Hall sensor inputs (H+, H–), dual driver outputs (A1, A2), lock detection via external capacitor on LD pin, speed indication on AL pin, and operation from 4 V to 28 V supply. It targets compact server fan control where minimal external components and automatic lock recovery are critical.

For engineers reviewing the TMP821DR datasheet, TMP821DR pinout, TMP821DR application, or TMP821DR equivalent, this page delivers verified functional modes, thermal limits, Hall hysteresis, output drive capability, and lock-detection timing behavior - all confirmed from TI's SLDS152A datasheet and orderable addendum.

Technical Context

The TMP821DR implements commutation logic using differential Hall inputs to generate complementary half-wave drive signals for external P-channel/N-channel H-bridge FETs. Its internal regulator powers the Hall amplifier and logic, while the LD pin controls lock-detection timing via external RC network - t_ON and t_OFF determined by V_{LD_CLAMP}, V_{LD_COMP}, I_LDC, and I_LDD.

Speed sensing is provided via open-drain AL output, which pulses at motor rotation frequency after startup delay; lock detection disables A1/A2 outputs when Hall signal stalls, then auto-restarts after capacitor discharge. The device operates across –40°C to +100°C ambient with junction-to-ambient thermal resistance of 97°C/W in SOIC-8 package.

Key Specifications

Pinout & Package

Package: SOIC-8 (D package), body size 4.90 mm × 3.91 mm, 1.75 mm max height, RoHS-compliant NIPDAU lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar motor predriver applications.

Compared with TMP822DR, TMP821DR trades overtemperature protection for lower supply current and identical lock-detection behavior; versus DRV10970PWPR, it provides discrete FET control and simpler Hall interface but requires external power stage design effort.

Availability

TMP821DR is available at Aetrix Electronics and suitable for server fan control, network equipment cooling, and industrial PC thermal management requiring stable component supply across long-life embedded programs.

Supply support for TMP821DR 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

Texas Instruments is a global semiconductor company delivering analog and embedded processing solutions, with leadership in motor control, power management, and precision analog technologies.

The TMP821DR belongs to TI's motor driver predriver product line, designed specifically for cost-sensitive, space-constrained BLDC fan applications requiring autonomous lock detection and speed telemetry without microcontroller dependency.

FAQ

What is the recommended external capacitor value for the LD pin on the TMP821DR?

The LD pin capacitor value determines lock-detection timing: t_ON = C_LD × (V_{LD_CLAMP} – V_{LD_COMP}) / I_LDC. With V_{LD_CLAMP} = 2.6 V typical, V_{LD_COMP} = 0.6 V, I_LDC = 3.45 μA, a 100 nF capacitor yields ~580 ms t_ON. TI's typical application uses 100 nF; values from 47 nF to 220 nF are common for 250–1200 ms hiccup intervals. Always verify timing with actual motor stall conditions in final design.

Can the TMP821DR drive motors directly, or does it require external MOSFETs?

The TMP821DR is a predriver only and cannot drive motors directly. Its A1 and A2 outputs deliver up to 70 mA each to gate-drive external P-channel high-side and N-channel low-side MOSFETs in a half-bridge configuration. The device lacks integrated power transistors; external FETs are mandatory for motor current handling. This architecture enables voltage and current scaling based on fan size and supply rail.

What is the function of the AL pin on the TMP821DR, and how is it used?

The AL pin on the TMP821DR serves dual functions: it outputs a pulse train proportional to motor RPM during normal operation, and pulls low during motor lock detection. It is an open-drain output capable of sinking 8 mA, allowing direct connection to a microcontroller GPIO with pull-up resistor. After power-on, AL remains high for several hundred milliseconds before transitioning to speed-proportional pulses - a behavior documented in Figure 4 of the TMP821DR datasheet.

Does the TMP821DR support 3-phase BLDC motors?

No, the TMP821DR is explicitly designed for two-phase half-wave operation and supports only two motor phases. Its block diagram, pinout (A1, A2 only), and functional description confirm it drives push-pull configured windings using differential Hall inputs for commutation. For 3-phase BLDC motors, TI recommends alternatives such as the DRV10970 or similar 3-phase drivers - the TMP821DR lacks the third output channel and associated logic.

What is the maximum ambient temperature for continuous operation of the TMP821DR?

The TMP821DR is rated for continuous operation from –40°C to +100°C ambient temperature, per its Recommended Operating Conditions table. At +100°C ambient, its 97°C/W junction-to-ambient thermal resistance limits total power dissipation to approximately 1.03 W to maintain junction temperature ≤125°C. Derating is required above 85°C ambient if power dissipation exceeds 0.5 W; layout with thermal vias and copper pour improves real-world margin.