Datasheet LTC3416 (Analog Devices) - 7

LTC3416
U OPERATIO
power MOSFET is turned off and the bottom power MOS-
Low Supply Operation
FET is switched on until either the overvoltage condition The LTC3416 is designed to operate down to an input clears or the bottom MOSFET’s current limit is reached. supply voltage of 2.25V. One important consideration at low input supply voltages is that the R
Voltage Tracking
DS(ON) of the P-channel and N-channel power switches increases. The Some microprocessors, ASIC and DSP chips need two user should calculate the power dissipation when the power supplies with different voltage levels. These sys- LTC3416 is used at 100% duty cycle with low input tems often require voltage sequencing between the core voltages to ensure that thermal limits are not exceeded. power supply and the I/O power supply. Without proper sequencing, latch-up failure or excessive current draw
Slope Compensation and Inductor Peak Current
may occur that could result in damage to the processor’s Slope compensation provides stability in constant fre- I/O ports or the I/O ports of supporting system devices quency architectures by preventing subharmonic oscilla- such as memory, FPGAs or data converters. To ensure tions at duty cycles greater than 50%. It is accomplished that the I/O loads are not driven until the core voltage is internally by adding a compensating ramp to the inductor properly biased, tracking of the core supply voltage and current signal at duty cycles in excess of 40%. Normally, the I/O supply voltage is necessary. the maximum inductor peak current is reduced when Voltage tracking is enabled by applying a voltage to the slope compensation is added. In the LTC3416, however, TRACK pin. When the voltage on the TRACK pin is below slope compensation recovery is implemented to keep the 0.8V, the feedback voltage will regulate to this tracking maximum inductor peak current constant throughout the voltage. When the tracking voltage exceeds 0.8V, tracking range of duty cycles. This keeps the maximum output control over the feedback voltage is gradually released. current relatively constant regardless of duty cycle. Full release of tracking control over the feedback voltage is achieved when the tracking voltage exceeds 1.05V.
Short-Circuit Protection
When the output is shorted to ground, the inductor current
Dropout Operation
decays very slowly during a single switching cycle. To When the input supply voltage decreases toward the prevent current runaway from occurring, a secondary output voltage, the duty cycle increases toward the maxi- current limit is imposed on the inductor current. If the mum on-time. Further reduction of the supply voltage inductor valley current exceeds 7.8A, the top power MOS- forces the main switch to remain on for more than one FET will be held off and switching cycles will be skipped cycle, eventually reaching 100% duty cycle. The output until the inductor current is reduced. voltage will then be determined by the input voltage minus the voltage drop across the internal P-channel MOSFET and the inductor. 3416fa 7