ISL91108IIAZ-T

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The ISL91108IIAZ-T is an integrated single-chip switch-mode dc-dc converter. It includes an integrated high-voltage power switch, gate drivers, oscillator, control logic and protection features. It is ideal for medium- to high-load current applications requiring a wide input voltage range, fast transient response and low output voltage ripple. It provides excellent efficiency, high operating frequency and configurable current limit.

ISL91108IIAZ-T is designed for automotive applications, it integrates many functions required for DC/DC converter, such as start-up circuit, UVLO delay time, OTM and etc. The regulating accuracy of this device is ±2.5% (max) at 12V, which ensures high precision regulation of output voltage. The adjustable switching frequency from 300K Hz to 1.1 MHz can be adjusted via the external resistor, allowing for efficient operation at various frequencies.

When the input voltage varies over a wide range, the switching frequency adjusts dynamically to optimize the efficiency and stay within the pre-set over-temperature limit. The switching frequency can be varied with an external resistor or with the switching duty cycle and power. The main operating frequency can be expanded or reduced with a duty cycle of up to +/- 10%.

ISL91108IIAZ-T is suitable for applications including automotive, industrial, computer, communication, audio-video, and home appliance power systems. It provides the high reliability and superior thermal performance with high transient response, low output voltage ripple, and adjustable output current. Besides, it provides an adjustable current limit circuit and power switch over-temperature monitoring for safety and security.

ISL91108IIAZ-T working principle is based on Pulse-Width Modulation (PWM). It utilizes a high-side NMOS and a low-side NMOS with embedded PWM logic to regulate the output voltage. The main feature of the PWM is that it uses a fixed regulated on-time to control the output voltage. The PWM controller monitors the output voltage and adjusts the on-time to regulate the output voltage to the desired level. The PWM output is fed to a CMOS buffer, which is connected to the power switch to control the switch operation.

When the voltage is applied across the inductor, a current is generated in the inductor. When the switch is in the on-state, this current increases, storing energy in the inductor. When the switch is in the off-state, this energy is released to the output. Due to this switching action, an output voltage is generated according to the duty cycle of the PWM signal. The duty cycle is adjusted to maintain the desired output voltage. The output current is controlled by adjusting the peak inductor current. This peak value is typically set using an external current sense resistor.

The ISL91108IIAZ-T is capable of multiple operating modes, such as pulse-skipping, PFM or PWM, to maximize efficiency and minimize the load noise. This switching mode power supply has a wide input voltage range of 5.5V to 36V, an adjustable output voltage range of 0.8V to 36V and an adjustable switching frequency range of 300K Hz to 1.1 MHz. It provides excellent performance with fast transient response, low output voltage ripple and adjustable current limit.

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