Rainbow-electronics MAX1844 Manual de usuario descargar pdf (Pagina 20)

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

20 ______________________________________________________________________________________

Dropout Design Example:

OUT

= 2.5V

fsw = 300kHz

K = 1.8µs, worst-case K = 2.97µs

OFF(MIN)

= 500ns

DROP1

= V

DROP2

= 100mV

h = 1.5

Calculating again with h = 1 gives the absolute limit of

dropout:

VV V

IN MIN()

. . .

()

µ×













25 01

05 1

297

01 01 313

VV V

IN MIN()

. .

.. .

()

µ×













25 01

05 15

297

01 01 348

AGND PLANE

PGND

PLANE

VIA TO IC OUT

POWER

GROUND

VIA TO IC

CS PIN

BYPASS

REF

BYPASS

USE AGND PLANE TO:

- BYPASS V

AND REF

- TERMINATE EXTERNAL FB, ILIM,

OVP, UVP DIVIDERS

- PIN-STRAP CONTROL INPUTS

USE PGND PLANE TO:

- BYPASS V

- CONNECT IC GND PIN

TO TOP-SIDE POWER GROUND

VIA TO POWER

GROUND

TOP SIDEBOTTOM SIDE

OUT

VIA R

VIA TO PGND PLANE

AND IC GND PIN

Figure 9. Power-Stage PC Board Layout Example

Table 5. Approximate K-Factor Errors

TON

SETTING

(kHz)

APPROXIMATE

K-FACTOR

ERROR (%)

MINIMUM V

AT V

OUT

= 2V

(V)

200 ±10 2.6

300 ±10 2.9

450 ±12.5 3.2

600 ±12.5 3.6

FACTOR

(µs)

3.3

2.2

1.7

1 2 ... 15 16 17 18 19 20 21 22 23

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Rainbow-electronics MAX1844 Manual de usuario Pagina 20

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