LT3495BEDDB(RevA) Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT3495BEDDB
(Rev.:RevA)

650mA/350mA Micropower Low Noise Boost Converter with Output Disconnect

Linear Technology 

LT3495/LT3495B/

LT3495-1/LT3495B-1

OPERATION

The LT3495 series utilizes a variable peak current, variable

off-time control scheme to provide high efficiency over a

wide range of output current.

The operation of the part can be better understood by

referring to the Block Diagram. The part senses the output

voltage by monitoring the voltage on the FB pin. The user

sets the desired output voltage by choosing the value of

the external top feedback resistor. The parts incorporate

a precision 76k bottom feedback resistor. Assuming that

output voltage adjustment is not used (CTRL pin is tied to

1.5V or greater), the internal reference (VREF = 1.235V) sets

the voltage at which FB will servo to during regulation.

The Switch Control block senses the output of the ampli-

fier and adjusts the switching frequency as well as other

parameters to achieve regulation. During the start-up of

the circuit, special precautions are taken to ensure that

the inductor current remains under control.

For the LT3495/LT3495-1, the switching frequency is never

allowed to fall below approximately 45kHz. Because of this,

a minimum load must be present to prevent the output

voltage from drifting too high. For most applications, this

minimum load is automatically generated within the part

via the Shunt Control block. The level of this current is

adaptable, removing itself when not needed to improve

efficiency at higher load levels. However when the input

voltage and output voltage are close, the internal shunt

current may not be large enough. Under this condition,

a minimum output load is required to prevent the output

voltage from drifting too high.

For the LT3495B/B-1, the minimum switching frequency

feature is disabled and the switching frequency can be as

low as zero. As a result, the output voltage will never drift

high and no minimum output load is required.

The LT3495 series also has a PMOS output disconnect

switch. The PMOS switch is turned on when the part is

enabled via the SHDN pin. When the parts are in shutdown,

the PMOS switch turns off, allowing the VOUT node to go to

ground. This type of disconnect function is often required

in power supplies.

The LT3495 series also sets a maximum switch on time of

10µs. This feature guarantees that the parts can continue

to deliver energy to the output even if the input supply

impedance becomes so large that the commanded peak

switch current is never reached.

The difference between the LT3495/LT3495B and LT3495-1/

LT3495B-1 is the level of the current limit. LT3495/LT3495B

have a typical peak current limit of 650mA while the

LT3495-1/LT3495B-1 have a typical peak current limit of

350mA. The differences between the LT3495 and LT3495B/

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

8

3495b1b1fa

Share Link: