Rainbow-electronics MAX1717 Manual de usuario descargar pdf (Pagina 10)

MAX1717

Dynamically Adjustable, Synchronous

Step-Down Controller for Notebook CPUs

10 ______________________________________________________________________________________

Pin Description

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components of Table 1, V+ = +12V, V

= V

= SKP/SDN = +5V, V

OUT

= 1.6V, T

= +25°C, unless otherwise noted.)

100µs/div

SHUTDOWN WAVEFORM

MAX1717 toc34

300kHz VOLTAGE POSITIONED, CIRCUIT 2,

PWM MODE, NO LOAD

A = V

OUT

, 1V/div

B = INDUCTOR CURRENT, 10A/div

C = SKP/SDN, 5V/div

100µs/div

SHUTDOWN WAVEFORM

MAX1717 toc35

300kHz VOLTAGE POSITIONED, CIRCUIT 2,

PWM MODE, I

OUT

= 12A

A = V

OUT

, 1V/div

B = INDUCTOR CURRENT, 10A/div

C = SKP/SDN, 5V/div

Feedback Remote-Sense Input. For nonvoltage-positioned circuits, connect FBS to V

OUT

directly at the

load. FBS internally connects to the integrator that fine tunes the DC output voltage. For voltage-positioned

circuits, connect FBS directly to FB near the IC to disable the FBS remote-sense integrator amplifier. To dis-

able all three integrator amplifiers, connect FBS to V

FBS5

Integrator Capacitor Connection. Connect a 100pF to 1000pF (470pF typ) capacitor from CC to GND to set

the integration time constant. CC can be left open if FBS is tied to V

CC6

Analog Supply Voltage Input for PWM Core. Connect V

to the system supply voltage (4.5V to 5.5V) with a

series 20Ω resistor. Bypass to GND with a 0.22µF (min) capacitor.

Fast Feedback Input. Connect FB to the junction of the external inductor and output capacitor for nonvolt-

age-positioned circuits (Figure 1). For voltage-positioned circuits, connect FB to the junction of the external

inductor and the positioning resistor (Figure 3).

FB4

Slew-Rate Adjustment Pin. Connect a resistor from TIME to GND to set the internal slew-rate clock. A 470kΩ

to 47kΩ resistor sets the clock from 38kHz to 380kHz, f

SLEW

= 150kHz x 120kΩ / R

TIME

TIME3

Combined Shutdown and Skip-Mode Control. Drive SKP/SDN to GND for shutdown. Leave SKP/SDN open for

low-noise forced-PWM mode, or drive to V

for normal pulse-skipping operation. Low-noise forced-PWM mode

causes inductor current recirculation at light loads and suppresses pulse-skipping operation. SKP/SDN can also

be used to disable over/undervoltage protection circuits and clear the fault latch by forcing it to 12V < SKP/SDN

< 15V (with otherwise normal PFM/PWM operation). Do not connect SKP/SDN to > 15V.

SKP/SDN

Battery Voltage Sense Connection. Connect V+ to input power source. V+ is used only for PWM one-shot

timing. DH on-time is inversely proportional to input voltage over a range of 2V to 28V.

V+1

FUNCTIONNAME

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 32 33

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Rainbow-electronics MAX1717 Manual de usuario Pagina 10

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