Diodes Incorporated Revamps Piezo Sound Driver to Drive Loads Up to 47nF

December 06, 2019 by Robin Mitchell

The PAM8940E can generate its own drive voltage while still driving large external loads up to 47nF.

This week, Diodes Incorporated announced an updated version of their popular sound driver IC, the PAM8940, for small, portable devices. In the past, the PAM8940 has been used in many applications, from simple user input feedback (beeps from pressing buttons) to alarms and warning signals.

Because the rise of the IoT industry has increased demand for sounders, Diodes Incorporated has released an enhanced version of the PAM8940: the PAM8940E.



PAM8940E. Image from Diodes Incorporated

The PAM8940E is a piezo sound driver that integrates a charge pump, control logic, level shifter, and output push-pull amplifier. The sound driver joins the many products on the market that incorporate audio generation. Diodes Incorporated states that this chip provides dual bridge outputs, runs from a single supply, and includes its own charge pump. 

It also allows up to three times charge pump voltage generation with a maximum output of approximately 30Vpp and operates in a temperature range of -40°C to +85°C.


Driving High Capacitive Loads

One major feature of the PAM8940E that separates it from competitors is its ability to drive capacitive loads up to 47nF. Most other competing devices can drive up to 15nF and require large input power supplies, but the PAM8940E can generate its own drive voltage while still driving large external loads.


Voltage Supply Range and Low EMI

The charge pump inside the PAM8940E operates at a fixed frequency of 100kHz and is used to boost the input voltage (1.5V to 5.5V) by a configurable multiplier of either 1x, 2x, and 3x giving a potential output of 27VPP when operating from a 4.5V.


Typical application schematic for the PAM8940E.

Typical application schematic for the PAM8940E. Image from Diodes Incorporated

Designers who may be concerned with EMI might appreciate that Diodes Incorporated offers drive technology that provides a low inrush current, low EMI, and high efficiency.


Wide Input Frequency Range

The PAM8940E can accept a wide range of input frequencies ranging from 20Hz to 300kHz; this allows for many different applications including audio and ultrasonic. The charge pump multiplier is controlled using two external enable signals, while a single input is used to read the square wave to be amplified.


Few External Components

External components are kept to a minimum with the device only requiring one decoupling capacitor on the supply voltage and two other capacitors for the charge pump pairs (requiring three capacitors in total).


Pin assignments of the PAM 8904E.

Pin assignments of the PAM 8904E. Image from Diodes Incorporated

This minimum external component count combined with the small package sizes (QFN16 and QFN12) means that the PAM8904E has minimum impact on the BOM price as well as the PCB real-estate.


Power Conservation

The PAM8904E includes built-in automatic shutdown and wakeup. Specifically, the IC offers automatic standby and wakeup control with 1µA sleep current. This technology helps to significantly reduce battery usage.


Timing chart: the PAM8904E

Timing chart: the PAM8904E will wait 42 ms after the input signal on DIN is removed before it enters into a low-current standby mode. Image from Diodes Incorporated

When combined with the protection of multiple devices, including thermal shutdown, over-current protection, and over-voltage protection, the PAM8904E should provide reliable operation for designers.


Applications for the New Version

Because the new sound driver is designed to enable devices to operate at extremely low voltages, it can be applicable for audio user interfaces, including health monitors, smart sensors, and alarms.

Diodes Incorporated foresees that this product's package size will make them suitable for any wearable device that may monitor the environment, too—for instance, with water, CO2, and smoke alarms.