The DRV103 is a low-side DMOS power switch with a pulse width modulation (PWM) output. Its robust design is used to drive electromechanical devices such as optimized valves, solenoid valves, relays, actuators, motors, and positioners. The DRV103 is also ideal for driving thermal equipment, as heaters, coolers, and lamps. PWM operation preserves power and reduces heat rise, resulting in higher reliability. In addition, adjustable PWM can well control the power delivered to the load. The DC to PWM output delay time and oscillator frequency are also externally adjustable. The DRV103 can be set to provide a strong initial closure, automatically switching to a "soft" hold mode for power saving. A resistor, analog-to-voltage or digital-to-analog (D/A) converter can control the duty cycle. An output OK flag indicates that thermal shutdown or overcurrent has occurred. Two software packages provide a choice of output current: 1.5A (SO-8) or 3A (using PowerPad™ with exposed metal SO-8 heatsink). The DRV103 is specified for -40°C to +85°C.

figure 1

Basic operation

The DRV103 is a low-side, DMOS power switch with a pulse width modulation (PWM) output for driving electro-mechanical and thermal devices. It is designed to optimize two types of applications: a two-state actuator (on/off) for loads such as solenoid valves and actuators; and a linear actuator for valves, positioners, heaters and bulbs. Its low 0.5Ω "ON" resistance, small size, adjustable delay to PWM mode, and adjustable duty cycle make it suitable for a wide range of applications. Figure 1 shows the basic circuit connections to operate the DRV103. A 1µF (22µF when driving high current loads) or larger tantalum bypass capacitor is recommended on the power supply pins. The input (pin 8) is level-triggered and compatible with standard TTL levels. Input voltages between +2.2V and +5.5V turn the device's output ON, while a voltage of 0V to +1.2V turns off the DRV103's output OFF. Input bias current is typically 1pA. Delay adjustment (pin 2) and duty cycle adjustment (pin 1) allow external adjustment of the PWM output signal. The delay adjust pin can be left floating for the minimum delay to PWM mode (typically 18µs) or a capacitor can be used to set a longer delay time. Resistors, analog voltages or voltages from AD/A converters can be used to control the duty cycle of the PWM output. The D/A converter must be able to sink a current of 2.75 µIREF (IREF = 1.3V/R frequency). Figure 2 shows a typical timing diagram with a delay adjust pin connected to a 3.9nF capacitor and the duty cycle set to 75% while the oscillator frequency is set to 1kHz. See "Delay Adjustment" and "Duty Cycle Adjustment" text equations and further explanation. Ground (pin 4) must be connected to system ground for the DRV103 to function. This serves as the load current ground path, as well as the DRV103 signal ground. Loads (relays, solenoids, valves, etc.) should be connected between the power supply side (pin 5) and the output (pin 6). For inductive loads, an external "flyback" diode is required, as shown in Figure 1. The role of the diode is to keep the continuous current flowing through the inductive load during the off-state PWM duty cycle. For remote loads, the external diode is strategically located adjacent to the DRV103. The internal ESD clamp diode between the output and the power supply is not intended to be used as a "flyback diode." The status line flag (Pin 7) provides fault conditions for overcurrent and thermal shutdown conditions. This pin is active low using a +0.3V output voltage normally under fault conditions.

figure 2

power supply

The DRV103 has excellent performance from a single +8V to +32V supply. Most behavior remains non-transient throughout the entire operating voltage range. The parameters vary significantly with operating voltage as shown in the typical performance curves. The DRV103 supply voltage should be ≥ the supply voltage on the load. Adjustable Delay Time (Initial 100 % Duty Cycle) A unique feature of the DRV103 is its ability to provide an initial constant DC output (100% duty cycle) and then switch to PWM mode output to save power. This feature is especially useful when driving a solenoid valve that has a very high pull-up requirement instead of a continuous hold current requirement. The duration of this constant DC output (before the PWM output starts) can be controlled externally via a capacitor from the delay adjustment connection (pin 2) according to the following equation to ground:

Leaving the delay adjust pin open leads to a constant output time of approximately 18µs. This duration of initial output can be reduced to less than 1µs by connecting this pin to 5V. Table 1 provides examples of delay times achieved with selected (constant output before PWM mode) capacitor values. The internal delay adjustment circuit is composed of a 3µA current source and a 2.6V comparator, as shown in Figure 3. Therefore, when the terminal voltage is less than 2.6V, the output device is 100% ON (DC output mode).

image 3

Table 1

Oscillator Frequency Adjustment

The DRV103 PWM output frequency can be easily pro-programmed over a wide range by connecting a resistor (R frequency) between the oscillator frequency ADJ pin (pin 3) and ground. Values in the range of 500Hz to 100kHz can be achieved with actual resistors, as shown in Table 2. Please refer to the "PWM Frequency vs. R Frequency" typical performance curve shown in Figure 4 for additional information. Although it is possible to operate oscillator frequencies below 500Hz, resistors higher than 10M will be required. The pin becomes a very high impedance node and, therefore, to noise interference, the PCB is sensitive to leakage if very high resistor values are used. See Figure 3 for a simplified circuit adjustment input for frequency.

Figure 4

Table 2