【Introduction】High-efficiency, low-EMI step-down regulators are widely used in automotive, industrial, medical, and telecom environments to power a wide variety of applications from multiple input sources. Especially in battery-operated applications, where a significant amount of time is spent in standby mode, all electrical circuits are required to operate at low quiescent current in order to extend battery run time.
The LT8606/LT8607/LT8608 are a family of monolithic step-down regulators optimized for applications with wide input voltage range, low EMI levels and small solution size. All devices in this family are available in thermally enhanced 10-pin MSE and 8-pin 2 mm x 2 mm DFN packages, allowing them to fit in tight spaces. As shown in Table 1, they differ in output current capability.
Table 1. LT860x Series Feature Comparison
The low IQ of the LT8606/LT8607/LT8608 is essential in battery powered applications where low no-load current must be maintained. These devices feature a Burst Mode® feature that draws only 2.5 μA of quiescent current from the input source, even when the output voltage is being regulated, to preserve battery life as long as possible. The wide input voltage range of 3 V to 42 V meets the demanding requirements of industrial and automotive applications, which are characterized by the lack of a stable, high-quality voltage source. The three devices are housed in a 10-pin MSE package and feature spread spectrum operation to meet ultra-low EMI emissions requirements.
Circuit Description and Function
Figure 1 shows a 5 V output power supply based on the 10-lead LT8607 regulator. The input voltage is extended up to 42 V, the output is set to 5 V (at 750 mA), and has a 2 MHz switching frequency. Only a few additional components are required to form this complete solution, including the Inductor L1 and several passive components. As shown in Figure 2, this circuit achieves a peak efficiency of 92.5%.
Figure 1. High efficiency LT8607 12 V to 5 V synchronous buck converter.
Figure 2. 12 V based on LT8606/LT8607/LT8608INto 5 VOUTEfficiency versus load current for a buck converter.
Burst Mode Operation Improves Light Load Efficiency
For battery powered applications, high efficiency and low idle current are very important features during light load operation and no-load standby mode. The 2.5 μA quiescent current and Burst Mode operation options of the LT8606/LT8607/LT8608 are ideal solutions to these requirements. The LT8606/LT8607/LT8608-based converters gradually reduce the switching frequency at light and no load conditions, thereby reducing switching power dissipation and maintaining low output voltage ripple. Figure 3 shows the light load efficiency of the solution shown in Figure 1.
Figure 3. Efficiency and power dissipation versus load current for the circuit shown in Figure 1.
High switching frequency and ultra-low EMI emissions
In automotive, industrial, computing and telecom environments, EMI/EMC compliance is required in addition to efficiency. Using higher switching frequencies reduces solution size, but often at the expense of increased EMI emissions. The LT8606/LT8607/LT8608’s integrated MOSFETs, built-in compensation circuitry, and 2.2 MHz operation minimize solution size, but they also achieve excellent EMI performance due to advanced process technology. Spread spectrum mode operation at the switching frequency can further reduce EMI emissions. Figure 4 presents the CISPR 25 EMI test results for the solution shown in Figure 1.
Figure 4. CISPR 25 radiated EMI performance of the circuit shown in Figure 1.
The LT8606/LT8607/LT8608 are easy-to-use monolithic step-down regulators with integrated power MOSFETs and built-in compensation circuitry. These devices are optimized for applications that require a wide input voltage range and low EMI noise. The 2.5 μA quiescent current and burst mode operation options of these devices make them an ideal solution for battery-operated buck converters that can significantly extend battery life. The 200 kHz to 2.2 MHz switching frequency range makes them suitable for most low power to micropower applications. The integrated MOSFET together with the switching frequency capability of up to 2.2 MHz greatly reduces the overall solution size. CISPR 25 scan results show their excellent radiated EMI performance, thus meeting the most stringent EMI standards.
● Wide input voltage range: 3.0V to 42V
● Ultra-low quiescent current Burst Mode® operation:
○ Output ripple
● High efficiency 2MHz synchronous operation:
○ at >92% efficiency (0.35A, 12VIN to 5VOUT)
● Maximum continuous output current: 350mA
● The shortest fast turn-on time: 35ns
● Adjustable and synchronizable frequency range: 200kHz to 2.2MHz
● Spread spectrum frequency modulation for low EMI
● Allows the use of small inductors
● Low dropout
● Peak current working mode
● Accurate 1V enable pin threshold
● Internal compensation
● Output soft start and tracking
● Small thermally enhanced 10-pin MSOP or 8-pin 2mm × 2mm DFN package