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　　Automotive lithium battery 18650 3.7vpower solution based on three-output voltage regulator

　　DC/DC converters for automotive applications must operate in extreme environments, where input transients can exceed nominal lithium battery 18650 3.7vvoltage by up to 5 times and last for hundreds of milliseconds, while under-hood temperatures can rise dramatically well beyond typical commercial The range that grade IC can withstand. In this harsh environment, space is at a premium, so even the most powerful devices must perform multiple functions.

　　Available in a compact 4mmx5mm QFN package or a thermally enhanced TSSOP package, the LT3694/LT3694-1 combines a 2.6A switching regulator and two low dropout linear regulators to meet these demanding requirements. This switching regulator requires only a single inductor and features an internal power switch, cycle-by-cycle current limit, and tracking/soft-start control. Each LDO requires only an external NPN pass transistor and has foldback current limit and tracking/soft-start control capabilities. When VIN exceeds 38V, an internal overvoltage detector shuts down the switching regulator, protecting the switch and Schottky rectifier. This allows the device's VIN pin to withstand transients up to 70V without damaging the device itself or the rectifier.

　　Switching Regulator for 4V to 36V Input

　　The LT3694/LT3694-1 include a 36V monolithic switching regulator capable of delivering up to 2.6A of output current from input voltages as low as 4V. The output voltage can be set as low as the feedback reference of 0.75V.

　　The regulator uses a current-mode, constant-frequency architecture that maintains simple loop compensation. External compensation allows customization of loop bandwidth, transient response, and phase margin.

　　Two low dropout linear regulators

　　The LT3694/LT3694-1 include two LDO linear regulators that use an external NPN pass transistor to provide up to 0.5A of output current. The base drive can provide up to 10mA of base current to the pass transistor and is current-limited. The LDO is internally compensated and stable with an output capacitor of 2.2µF or greater. The LDO uses the same 0.75V reference as the switching regulator.

　　If the BIAS pin is at least 0.9V higher than the DRIVE pin voltage, then the LDO draws drive current from the BIAS pin, otherwise the LDO draws drive current from VIN. This reduces the LDO's power consumption, especially when VIN is relatively high.

　　The LDO implements foldback current limiting by monitoring the sense resistor on the collector of the NPN pass transistor. The initial threshold is set to 60mV, but returns as VFB drops until VFB=0 and the threshold is 26mV. A 0.1Ω sense resistor sets the operating current limit to 600mA, but the short-circuit current limit drops to 260mA. This reduces the power consumption of the pass transistor when the output is shorted.

　　Figure 1: LT3694/LT3694-1 used in a wide input range, 3 output application

　　The LDO can be shut down by pulling the FB pin above 1.25V with at least 30µA. If you need independent control of the LDOs, you can force the output of each LDO to equal 0V by pulling its TRK/SS pin low. If tracking or soft-start functionality is required, use an open-drain output in parallel with the tracking or soft-start circuit described below. If tracking and soft-start are not required, a standard CMOS output (1.8V to 5V) with a 1kΩ series resistor will do the job just fine.

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