Rainbow-electronics MAX1712 Bedienungsanleitung PDF herunterladen (Seite 25)

MAX1710/MAX1711/MAX1712

High-Speed, Digitally Adjusted

Step-Down Controllers for Notebook CPUs

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D1 Q2

BATT

GND IN

COUT

VIA TO FB

NEAR COUT+

VIA TO LX

VIA TO SOURCE

OF Q2

VIA TO PGND

NEAR Q2 SOURCE

INDUCTOR DISCHARGE PATH HAS LOW DC RESISTANCE.

VIA TO FBS

VIA TO GNDS

GND

OUT

REF

GND

ALL ANALOG GROUNDS

CONNECT TO GND ONLY.

NOTES: "STAR" GROUND IS USED.

D1 IS DIRECTLY ACROSS Q2.

CONNECT GND TO PGND

BENEATH IC, 1 POINT ONLY.

SPLIT ANALOG GND PLANE AS SHOWN.

LIM

MAX1710

MAX1711

MAX1712

CIN

Figure 11. Power-Stage PC Board Layout Example

recovery overshoot, and c) minimize input surge cur-

rents.

The optional 74HC86 exclusive-OR gate detects code

transitions on each of the four most-significant DAC

inputs. The transition detector output goes to a precision

pulse stretcher, a timer that extends the pulse for 75µs

(nominal). This signal then feeds three circuits: the

power-good detector, the SKIP input, and the ILIM cur-

rent-limit control input, thus reducing the current-limit

threshold during the transition interval (in order to reduce

battery current surges). Likewise, SKIP going high

asserts forced PWM mode in order to drag the output

voltage down to the new value. Forced PWM mode is

incompatible with good light-load efficiency due to

inductor-current recirculation losses and gate-drive loss-

es. Therefore, SKIP is driven high only during the 100µs

max transition interval.

The power-good output signal is the logical OR of the

75µs timer signal and the MAX1711/MAX1712 PGOOD

signal. The internal PGOOD detector circuit monitors

only output undervoltage; PGOOD will probably go low

during upward transitions, but not downward. The final

power-good output will always go low for at least 75µs

due to the timer signal.

Load current capability is 15A peak and 12A continuous

over a 10V to 22V input range. All three MOSFETs

require good heatsinking. See the MAX1711 EV kit man-

ual for a complete bill of materials.

PC Board Layout Guidelines

Careful PC board layout is critical to achieving low

switching losses and clean, stable operation. The

switching power stage requires particular attention

(Figure 11). If possible, mount all of the power compo-

nents on the top side of the board with their ground ter-

minals flush against one another. Follow these

guidelines for good PC board layout:

1 2 ... 20 21 22 23 24 25 26 27 28

MAX1710/MAX1711/MAX1712 1
MAX1710/MAX1711 14

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