MCP16301HT-ESLASHCH datasheet(20/40 Pages) MICROCHIP

20 / 40 page

MCP16301/H

DS20005004D-page 20

 2011-2015 Microchip Technology Inc.

5.9

Boost Capacitor

The boost capacitor is used to supply current for the

internal high-side drive circuitry that is above the input

voltage. The boost capacitor must store enough energy

to completely drive the high-side switch on and off. A

0.1 µF X5R or X7R capacitor is recommended for all

applications. The boost capacitor maximum voltage is

5.5V, so a 6.3V or 10V rated capacitor is

recommended. In case of a noise-sensitive application,

an additional resistor in series with the boost capacitor,

that will reduce the high-frequency noise associated

with switching power supplies, can be added. A typical

value for the resistor is 82

.

5.10

Thermal Calculations

The MCP16301/H devices are available in a SOT-23-6

package. By calculating the power dissipation and

applying the package thermal resistance (

JA), the

junction temperature is estimated. The maximum

continuous junction temperature rating for the

MCP16301/H devices is +125°C.

To quickly estimate the internal power dissipation for

the switching step-down regulator, an empirical

calculation using measured efficiency can be used.

Given the measured efficiency, the internal power

dissipation is estimated by Equation 5-7. This power

dissipation

includes

all

internal

and

external

component losses. For a quick internal estimate,

subtract the estimated Schottky diode loss and inductor

ESR loss from the PDIS calculation in Equation 5-7.

EQUATION 5-7:

TOTAL POWER

DISSIPATION ESTIMATE

The difference between the first term, input power, and

the second term, power delivered, is the total system

power dissipation. The freewheeling Schottky diode

losses are determined by calculating the average diode

current and multiplying by the diode forward drop. The

inductor losses are estimated by PL =IOUT2 xLESR.

EQUATION 5-8:

DIODE POWER

DISSIPATION ESTIMATE

EXAMPLE 5-5:

5.11

PCB Layout Information

Good printed circuit board layout techniques are

important to any switching circuitry, and switching

power supplies are no different. When wiring the

switching high-current paths, short and wide traces

should be used. Therefore, it is important that the input

and output capacitors be placed as close as possible to

the MCP16301/H devices to minimize the loop area.

The feedback resistors and feedback signal should be

routed away from the switching node and the switching

current loop. When possible, ground planes and traces

should be used to help shield the feedback signal and

minimize noise and magnetic interference.

A good MCP16301/H layout starts with CIN placement.

CIN supplies current to the input of the circuit when the

switch is turned on. In addition to supplying

high-frequency switch current, CIN also provides a

stable voltage source for the internal MCP16301/H

circuitry. Unstable PWM operation can result if there

are excessive transients or ringing on the VIN pin of the

MCP16301/H devices. In Figure 5-1, CIN is placed

close to pin 5. A ground plane on the bottom of the

board provides a low resistive and inductive path for

the return current. The next priority in placement is the

freewheeling current loop formed by D1, COUT and L,

while strategically placing COUT return close to CIN

return. Next, CB and DB should be placed between the

boost pin and the switch node pin SW. This leaves

space close to the VFB pin of the MCP16301/H devices

to place RTOP and RBOT. RTOP and RBOT are routed

away from the Switch node so noise is not coupled into

the high-impedance VFB input.

VOUT IOUT



Efficiency

-------------------------------





VOUT IOUT





–

PDis

PDiode

–

 I

OUT







VIN

=10V

VOUT

=5V

IOUT

=0.4A

Efficiency

= 90%

Total System Dissipation

= 222 mW

LESR

=0.15



=24 mW

Diode VF

= 0.50

D= 50%

PDiode

=125 mW

MCP16301/H internal power dissipation estimate:

PDIS -PL -PDIODE =73mW

JA

=198°C/W

Estimated Junction

Temperature Rise

=+14.5°C

MCP16301HT-E/CH датащи(PDF) 20 Page - Microchip Technology

MCP16301HT-E/CH датащи(HTML) 20 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

датащи скачать

ссылки URL