Rainbow-electronics MAX1644 Manual de usuario descargar pdf (Pagina 5)

MAX1644

2A, Low-Voltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(Circuit of Figure 1, T

= +25°C, unless otherwise noted.)

NAME FUNCTION

SHDN

Shutdown Control Input. Drive SHDN low to disable the reference, control circuitry, and internal

MOSFETs. Drive high or connect to V

for normal operation.

Pin Description

OUT

20mV/div

20µs/div

LINE-TRANSIENT RESPONSE

MAX1644-10

OUT

= 1.5V, I

OUT

= 2A

OUT

50mV/div

20µs/div

LOAD-TRANSIENT RESPONSE

(FBSEL = REF)

MAX1644-11

= 3.3V, V

OUT

= 1.5V

2, 4 IN Supply Voltage Input for the internal PMOS power switch

3, 14, 16 LX

Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch. Connect

the inductor from this node to output filter capacitor and load.

5 SS Soft-Start. Connect a capacitor from SS to GND to limit inrush current during start-up.

6 COMP

Integrator Compensation. Connect a capacitor from COMP to V

for integrator compensation. See the

Integrator Amplifier section.

7 TOFF

Off-Time Select Input. Sets the PMOS power switch off-time during constant-off-time operation. Connect a

resistor from TOFF to GND to adjust the PMOS switch off-time.

8 FB

Feedback Input for both preset-output and adjustable-output operating modes. Connect directly to

output for fixed-voltage operation or to a resistor-divider for adjustable operating modes.

9 GND Analog Ground

10 REF Reference Output. Bypass REF to GND with a 1µF capacitor.

11 FBSEL

Feedback Select Input. Selects AC load-regulation error and output voltage. See Table 2 for program-

ming instructions.

12 V

Analog Supply Voltage Input. Supplies internal analog circuitry. Bypass V

with a 10Ω and 2.2µF low-

pass filter. See Figure 1.

13, 15 PGND Power Ground. Internally connected to the internal NMOS synchronous-rectifier switch.

1 2 3 4 5 6 7 8 9 10 11

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Rainbow-electronics MAX1644 Manual de usuario Pagina 5

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