Rainbow-electronics MAX8620 Manual de usuario descargar pdf (Pagina 9)

Voltage-Positioning Load Regulation

As seen in Figure 2, the MAX8620Y uses a unique step-

down converter feedback network. By taking feedback

from the LX node through R1, the usual phase lag due

to the output capacitor is removed, making the loop

exceedingly stable and allowing the use of a very small

ceramic output capacitor. This configuration causes the

output voltage to shift by the inductor series resistance

multiplied by the load current. This output-voltage shift

is known as voltage-positioning load regulation.

Voltage-positioning load regulation greatly reduces

overshoot during load transients, which effectively

halves the peak-to-peak output-voltage excursions

compared to traditional step-down converters. See the

Load-Transient Response graph in the Typical

Operating Characteristics section.

Two low-dropout, low-quiescent-current, high-accuracy

linear regulators supply loads up to 300mA each. The

LDO output voltages are set using SEL1 and SEL2 (see

Table 1). As shown in Figure 3, the LDOs include an

internal reference, error amplifiers, p-channel pass tran-

sistors, internal-programmable voltage-dividers, and an

OUT1 power-good comparator. Each error amplifier

compares the reference voltage to a feedback voltage

and amplifies the difference. If the feedback voltage is

lower than the reference voltage, the pass-transistor

gate is pulled lower, allowing more current to pass to

the outputs and increasing the output voltage. If the

feedback voltage is too high, the pass-transistor gate is

pulled up, allowing less current to pass to the output.

MAX8620Y

µPMIC for Microprocessors or DSPs

in Portable Equipment

_______________________________________________________________________________________ 9

OUT1

OUT2

GND

IN1

HF_PWR

2.6V

300mA

100kΩ

PWR_ON

SEL1

RESET

SEL2

EN2

RESET IN

OUT3,

500mA

OUT2

4.7µF

OUT1

4.7µF

OUT3

2.2µF

10µF

0.01µF

150pF

DSP

µP

I/O

ANALOG

ON/OFF

CORE

150kΩ

2.2µH

Li+

CELL

2.6V

300mA

75kΩ

POWER-ON

KEY

BATT

1MΩ

IN2

MAX8620Y

SEL1 SEL2 OUT1 OUT2

IN1 IN1 3.00V 2.50V

IN1 OPEN 2.85V 2.85V

IN1 GND 3.00V 3.00V

OPEN IN1 3.30V 2.50V

OPEN OPEN 2.80V 2.60V

OPEN GND 3.30V 1.80V

GND IN1 2.85V 2.60V

GND OPEN 2.60V 2.60V

GND GND 1.80V 2.60V

Figure 2. Typical MAX8620Y DSP or µP Application

Table 1. MAX8620Y Output-Voltage

Selection

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 17 18

MAX8620Y 1

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Rainbow-electronics MAX8620 Manual de usuario Pagina 9

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