Tool/software:
Subject: DRV2603RUNR (ERM) — no vibration under load; OUT± show ±1.5 V to GND when unloaded
Part: DRV2603RUNR (ERM mode)
Supply: 3.3 V
MCU: ESP32-C6
Hook-up (simplified):
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VDD → 3.3 V (0.1 µF nearby; also tried 47 µF bulk).
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LRA/ERM pin → GND (ERM mode).
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EN ← MCU IO21 (active-high).
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IN ← MCU IO20 (GPIO HIGH for ON / LOW for OFF). Also tried IN hard-tied to 3.3 V via 10 kΩ and toggling EN only.
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Motor between OUT+
OUT−. -
MCU and DRV2603 grounds common.
Symptoms:
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With no motor connected, each output measured to GND sits around ±1.5 V (VDD=3.3 V).
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With motor connected, the differential OUT+
OUT− drops to ~0 V, motor does not vibrate. -
A simple LED to GND from an output will light, but the motor won’t run.
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Toggling EN and IN from the MCU (and also hard-wiring EN=VDD, IN=VDD) gives the same result: no differential drive under load.
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Motor itself works when powered directly from a bench supply.
What we’ve tried:
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Verified wiring (motor strictly on OUT+
OUT−, LRA/ERM low). -
Confirmed EN=HIGH, IN=HIGH with a meter during “ON.”
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Added bulk capacitance at VDD; same behavior.
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Ensured common ground with MCU.
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Also tested “EN-only” mode (IN strapped HIGH) → still no motion.
Questions:
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Under what conditions would DRV2603 remove drive / show ~0 V differential only when a load is present (e.g., OCP, UVLO, thermal)? Does the device latch or auto-recover?
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Is DC drive on IN (IN=HIGH, no PWM) fully supported for ERM, or should we always provide ≥10 kHz PWM? Any minimum ON time or sequencing when using EN+IN?
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Recommended bulk capacitance at VDD for ERM startup current at 3.3 V? Any guidance on supply impedance to avoid UVLO/OCP during spin-up?
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Any known pin-strap or layout gotchas that could cause outputs to sit mid-rail unloaded but collapse under load?
I can share the motor datasheet, exact coil resistance is 31 ohms, scope captures of VDD, IN, and OUT+OUT− during turn-on, and the PCB layout if helpful. Thanks!
