The ISL7823x devices shown in Figure 6 are designed to operate from lower input voltages (+5.5 V down to 2.7 V). As a result, most of their transistors use a smaller geometry, take up less die area and can switch at higher speeds. And since the gate of the upper P-channel FET is driven with the same supply, the signal swing is lower than if an N-channel arrangement is used. This also enables faster switching. The devices can operate with a clock as high as 4 MHz, and when set to switch at 2MHz, they can achieve a guaranteed minimum on time of only 100ns. Since 2MHz has a period of 500ns, the devices can down convert with a guaranteed 20% minimum duty ratio. This enables the regulators to output a wide range of voltages while operating at a high frequency.
A 100% duty ratio is possible because no time is required to charge a boot capacitor (the ISL7823x devices do not use one). Moreover, no boot capacitor equates to no radiated fields. The high 2MHz switching frequency also enables the use of a smaller power inductor and lower valued capacitors on the regulator’s input and output. It’s also above the AM radio band and helps prevent EMI at these frequencies.
Pass Inspection with a Wettable Flank QFN Package
All three of the ISL7823x devices are available in 5mm x 5mm 16-lead wettable flank thin quad flat no-lead (WFQFN) packages with an exposed pad for improved thermal performance. Because they offer 3A, 4A or 5A output current options, it’s easy to upgrade a design just by dropping in a new IC with no change in the PCB layout. This saves development costs and time! In addition, the wettable flank