Rainbow-electronics MAX1842 Bedienungsanleitung PDF herunterladen (Seite 8)

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with

Synchronous Rectification and Internal Switches

8 _______________________________________________________________________________________

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

MAX1842

LOAD-TRANSIENT RESPONSE

OUTPUT

50mV/div

2A/div

MAX1842 toc17

10µs/div

MAX1842

LINE-TRANSIENT RESPONSE

INPUT

2V/div

OUTPUT

20mV/div

AC-COUPLED

MAX1842 toc18

20µs/div

OUT

= 2.5A, V

OUT

= 1.5V, R

TOFF

= 100kΩ, L = 2.2µH

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 the output filter capacitor and load.

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

6 COMP

Integrator Compensation. Connect a capacitor from COMP to V

for integrator compensation. See

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 resistive 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 output voltage. See Table 3 for programming 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.

Typical Operating Characteristics (continued)

(Circuit of Figure 1, T

= +25°C, unless otherwise noted.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

MAX1742/MAX1842 1

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