WT8509 Audio Amplifier IC
8W (AB) / 8.5W (D) · Switchable AB/D Class · 2.5–9.2V · 90% Efficiency · ESOP8
The WT8509 is a high‑efficiency, ultra‑low EMI mono audio amplifier with switchable AB and D class operation modes. It delivers 8W (AB class) or 8.5W (D class) into a 4Ω load at 8.5V, making it ideal for high‑power portable and multimedia applications. The D‑class mode features a filter‑free PWM architecture that reduces external components, PCB area, and system cost while achieving up to 90% efficiency. The device offers an ultra‑low < 0.1µA shutdown current, wide supply voltage range (2.5–9.2V), and comprehensive protection including over‑current, short‑circuit, and thermal protection. Housed in a thermally‑enhanced ESOP8 package, the WT8509 is perfect for laptops, multimedia speakers, and portable amplification systems.
- 8W (AB) / 8.5W (D) @ 8.5V, 4Ω
- Switchable AB/D class – flexible operation
- 90% efficiency in D‑class mode
- < 0.1µA shutdown current
- 2.5–9.2V wide supply range
- ESOP8 package with thermal pad
WT8509 Key Features
Electrical Specifications (TA = 25°C)
| Parameter | Conditions | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Supply Voltage | — | 2.5 | — | 9.2 | V |
| Shutdown Current | VSD = 0V | — | — | 0.1 | µA |
| Quiescent Current (D Class) | VDD=7.5V, no load | — | 4.6 | — | mA |
| Quiescent Current (D Class) | VDD=3.6V, no load | — | 2.5 | — | mA |
| Output Power (D Class) | 4Ω, THD+N≤10%, VDD=8.5V | — | 8.5 | — | W |
| Output Power (AB Class) | 4Ω, THD+N≤10%, VDD=8.5V | — | 8.0 | — | W |
| Output Power (D Class) | 8Ω, THD+N≤10%, VDD=7.4V | — | 3.5 | — | W |
| Output Power (AB Class) | 8Ω, THD+N≤10%, VDD=7.4V | — | 3.5 | — | W |
| Efficiency (D Class) | 5V, 8Ω, 0.6W | — | 90 | — | % |
| PSRR | VDD=2.5–9.2V, 217Hz | — | –80 | — | dB |
| Start‑up Time | — | — | 200 | — | ms |
| Output Offset Voltage | VIN=0V, AV=2 | — | 5 | 25 | mV |
D‑class mode delivers higher output power and efficiency. AB‑class mode offers traditional linear amplifier characteristics with lower EMI.
Pin Description – ESOP8
| Pin | Name | Function |
|---|---|---|
| 1 | SD | Shutdown (high = active, low = shutdown) |
| 2 | ABD | Mode select (high = D class, low = AB class) |
| 3 | IN+ | Non‑inverting input |
| 4 | IN− | Inverting input |
| 5 | VDD | Power supply (2.5–9.2V) |
| 6 | VO+ | Positive output |
| 7 | VO− | Negative output |
| 8 | GND | Ground |
| 0 (Pad) | E‑GND | Exposed thermal pad – connect to GND with large copper area |
The exposed pad (pin 0) must be soldered to ground and provided with adequate thermal copper area for heat dissipation.
Mode Selection & Control
| SD Pin | ABD Pin | Mode |
|---|---|---|
| Low (0) | Don’t care | Shutdown – < 0.1µA |
| High (1) | Low (0) | AB Class – linear operation |
| High (1) | High (1) | D Class – high‑efficiency PWM |
The SD pin must be driven high (>2.0V) for normal operation. The ABD pin selects the amplifier mode; D class is recommended for battery‑powered applications requiring high efficiency.
Protection & Safety Features
- Over‑Current Protection (OCP): Shuts down the device during excessive output current conditions.
- Short‑Circuit Protection (SCP): Protects against output short to ground or supply.
- Thermal Shutdown (TSD): Disables the output stage when junction temperature exceeds 150°C.
- Under‑Voltage Protection (UVP): Prevents operation below safe voltage levels.
- Auto‑Recovery: The device automatically resumes normal operation after fault conditions are removed.
Design & Layout Recommendations
Key design guidelines:
- Decoupling: Place a 1µF ceramic capacitor as close as possible to the VDD pin. A 470µF or larger capacitor is recommended for low‑frequency noise filtering.
- Gain setting: AV = RF / RIN (differential). Use 1% tolerance resistors for optimal performance.
- Input filtering: The input capacitor (CIN) forms a high‑pass filter: fC = 1/(2π RIN CIN). For 217Hz noise rejection, choose appropriate values.
- Output filter: While the device can operate without a filter, use a ferrite bead or LC filter (e.g., 33µH, 2.3A inductor) for EMC compliance in sensitive environments.
- Thermal management: The exposed pad must be soldered to a large copper ground plane with multiple vias for heat dissipation.
For EMC compliance, add a LC π‑filter (10–22µH, 2.3A) on the supply line and use 0Ω resistors or ferrite beads for analog/digital ground separation.
WT8509 Applications
Why Choose WT8509
FAQs
What is the WT8509?
A high‑power mono audio amplifier with switchable AB/D class modes, delivering 8W (AB) or 8.5W (D) into 4Ω at 8.5V.
What is the WT8509 supply voltage range?
2.5V to 9.2V, ideal for dual‑cell Li‑ion battery applications.
How much current does WT8509 draw in shutdown?
Less than 0.1µA, maximizing battery life in standby.
What is the difference between AB and D modes?
AB class offers linear audio quality with lower EMI; D class provides high efficiency (up to 90%) for battery‑powered applications.
Does WT8509 need an output filter?
No – the filter‑free PWM architecture eliminates the need for output filters in most applications, but an LC filter is recommended for EMC compliance.
What protection features does it have?
Over‑current, short‑circuit, thermal shutdown, under‑voltage protection, and auto‑recovery.
How do I select the mode?
Drive the ABD pin high for D class or low for AB class. The SD pin must be high for active operation.
What is the package type?
ESOP8 with an exposed thermal pad that must be soldered to ground with good thermal copper area.
Note: The WT8509 requires proper PCB layout for optimal thermal performance. The exposed pad (pin 0) must be soldered to a large ground plane with multiple thermal vias. For maximum output power, ensure the power supply can deliver sufficient current and that the speaker load is within the recommended range. Refer to the datasheet for detailed application guidelines, characteristic curves, and complete electrical specifications.
