Datasheet LT3495, LT3495B, LT3495-1, LT3495B-1 (Analog Devices) - 8

LT3495/LT3495B/ LT3495-1/LT3495B-1
OPERATION
The LT3495 series utilizes a variable peak current, variable voltage and output voltage are close, the internal shunt off-time control scheme to provide high efficiency over a current may not be large enough. Under this condition, wide range of output current. a minimum output load is required to prevent the output The operation of the part can be better understood by voltage from drifting too high. referring to the Block Diagram. The part senses the output For the LT3495B/B-1, the minimum switching frequency voltage by monitoring the voltage on the FB pin. The user feature is disabled and the switching frequency can be as sets the desired output voltage by choosing the value of low as zero. As a result, the output voltage will never drift the external top feedback resistor. The parts incorporate high and no minimum output load is required. a precision 76k bottom feedback resistor. Assuming that The LT3495 series also has a PMOS output disconnect output voltage adjustment is not used (CTRL pin is tied to switch. The PMOS switch is turned on when the part is 1.5V or greater), the internal reference (VREF = 1.235V) sets enabled via the SHDN pin. When the parts are in shutdown, the voltage at which FB will servo to during regulation. the PMOS switch turns off, allowing the VOUT node to go to The Switch Control block senses the output of the ampli- ground. This type of disconnect function is often required fier and adjusts the switching frequency as well as other in power supplies. parameters to achieve regulation. During the start-up of The LT3495 series also sets a maximum switch on time of the circuit, special precautions are taken to ensure that 10µs. This feature guarantees that the parts can continue the inductor current remains under control. to deliver energy to the output even if the input supply For the LT3495/LT3495-1, the switching frequency is never impedance becomes so large that the commanded peak allowed to fall below approximately 45kHz. Because of this, switch current is never reached. a minimum load must be present to prevent the output The difference between the LT3495/LT3495B and LT3495-1/ voltage from drifting too high. For most applications, this LT3495B-1 is the level of the current limit. LT3495/LT3495B minimum load is automatically generated within the part have a typical peak current limit of 650mA while the via the Shunt Control block. The level of this current is LT3495-1/LT3495B-1 have a typical peak current limit of adaptable, removing itself when not needed to improve 350mA. The differences between the LT3495 and LT3495B/ efficiency at higher load levels. However when the input LT3495-1/LT3495B-1 are listed in Table 1.
Table 1. Difference Between LT3495 and LT3495B/LT3495-1/LT3495B-1 PART SWITCH CURRENT LIMIT (mA) MINIMUM SWITCHING FREQUENCY (kHz) MINIMUM OUTPUT LOAD REQUIREMENT
LT3495 650 45 Required under certain conditions LT3495B 650 0 Not Required LT3495-1 350 45 Required under certain conditions LT3495B-1 350 0 Not Required 3495b1b1fa 8 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Infomation Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts