LTC3783IFETRPBF 查看數據表（PDF） - Linear Technology

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LTC3783IFETRPBF

PWM LED Driver and Boost, Flyback and SEPIC Controller

Linear Technology 

LTC3783

OPERATION

INTVCC Regulator Bypassing and Operation

An internal, P-channel low dropout voltage regulator pro-

duces the 7V supply which powers the gate drivers and

logic circuitry within the LTC3783 as shown in Figure 3.

The INTVCC regulator can supply up to 50mA and must be

bypassed to ground immediately adjacent to the IC pins

with a minimum of 4.7µF low ESR or ceramic capacitor.

Good bypassing is necessary to supply the high transient

currents required by the MOSFET gate driver.

For input voltages that don’t exceed 8V (the absolute

maximum rating for INTVCC is 9V), the internal low dropout

regulator in the LTC3783 is redundant and the INTVCC pin

can be shorted directly to the VIN pin. With the INTVCC

pin shorted to VIN, however, the divider that programs the

regulated INTVCC voltage will draw 15µA from the input sup-

ply, even in shutdown mode. For applications that require

the lowest shutdown mode input supply current, do not

connect the INTVCC pin to VIN. Regardless of whether the

INTVCC pin is shorted to VIN or not, it is always necessary

to have the driver circuitry bypassed with a 4.7µF low ESR

ceramic capacitor to ground immediately adjacent to the

INTVCC and GND pins.

In an actual application, most of the IC supply current is

used to drive the gate capacitance of the power MOSFET.

As a result, high input voltage applications in which a

large power MOSFET is being driven at high frequencies

can cause the LTC3783 to exceed its maximum junction

temperature rating. The junction temperature can be

estimated using the following equations:

IQ(TOT) = IQ + f • QG

PIC = VIN • (IQ + f • QG)

TJ = TA + PIC • qJA

The total quiescent current IQ(TOT) consists of the static

supply current (IQ) and the current required to charge and

discharge the gate of the power MOSFET. The 16-lead FE

package has a thermal resistance of qJA = 38°C/W and

the DHD package has an qJA = 43°C/W

As an example, consider a power supply with VIN = 12V

and VOUT = 25V at IOUT = 1A. The switching frequency is

300kHz, and the maximum ambient temperature is 70°C.

The power MOSFET chosen is the Si7884DP, which has a

maximum RDS(ON) of 10mΩ (at room temperature) and

1.230V

R2

–

+

LOGIC

VIN

INPUT

SUPPLY

6V TO 36V

P-CH

CIN

R1

7V INTVCC

DRIVER

GATE

CVCC

4.7µF

X5R

6V-RATED

M1

POWER

MOSFET

GND

3783 F03

GND

PLACE AS CLOSE AS

POSSIBLE TO DEVICE PINS

Figure 3. Bypassing the LDO Regulator and Gate Driver Supply

3783fb

11

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