MAX8560 Просмотр технического описания (PDF) - Maxim Integrated

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MAX8560

4MHz, 500mA Synchronous Step-Down DC-DC Converters in Thin SOT and TDFN

Maxim Integrated 

4MHz, 500mA Synchronous Step-Down

DC-DC Converters in Thin SOT and TDFN

PIN

MAX8560

MAX8561

MAX8562

1

1

2

7

3

8

4

6

—

2

5

3

—

5

—

4

—

EP

Pin Description

NAME

FUNCTION

IN

GND

SHDN

FB

PGND

LX

ODO

ODI

EP

Supply Voltage Input. 2.7V to 5.5V. Bypass with a 2.2µF ceramic capacitor as close as

possible to the IN and GND pins.

Ground

Active-Low Shutdown Input. Connect to IN or logic high for normal operation. Connect to

GND or logic low for shutdown mode.

Voltage Feedback Input. FB regulates to 0.6V nominal. Connect FB to the center of an

external resistive divider (see the Setting the Output Voltage section).

Power Ground. Must connect to GND.

Inductor connection to the drains of the internal P-channel and N-channel MOSFETs.

Auxiliary Open-Drain Output

Digital Input for Open-Drain MOSFET. Connect to IN or logic high to internally pull ODO

low (and force the MAX8562 into 100% duty cycle). Connect to GND or logic low to force

ODO to high impedance (MAX8561) or 10kΩ pullup from ODO to IN (MAX8562).

Exposed Pad. Connect to GND.

Detailed Description

The MAX8560/MAX8561/MAX8562 step-down converters

deliver a guaranteed 500mA at output levels from 0.6V to

2.5V. They use a proprietary hysteretic-PWM control

scheme that switches up to 4MHz, allowing a trade-off

between efficiency and tiny external components. At light

loads below 100mA, the MAX8560/MAX8561/MAX8562

automatically switch to pulse-skipping mode to keep qui-

escent supply current as low as 40µA (typ).

Control Scheme

A proprietary hysteretic-PWM control scheme ensures

high efficiency, fast switching, fast transient response,

low output ripple, and physically tiny external compo-

nents. This control scheme is simple: when the output

voltage falls below the regulation threshold, the error

comparator begins a switching cycle by turning on the

high-side switch. This switch remains on until the mini-

mum on-time expires and the output voltage is in regu-

lation or the current-limit threshold is exceeded. Once

off, the high-side switch remains off until the minimum

off-time expires and the output voltage falls again,

below the regulation threshold. During this period, the

low-side synchronous rectifier turns on and remains on

until either the high-side switch turns on again or the

inductor current approaches zero. The internal syn-

chronous rectifier eliminates the need for an external

Schottky diode.

Voltage-Positioning Load Regulation

As seen in the Typical Operating Circuit, the

MAX8560/MAX8561/MAX8562 use a unique 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 capaci-

tor. This configuration causes the output voltage to shift

by the inductor series resistance multiplied by the load

current. This voltage-positioning load regulation greatly

reduces overshoot during load transients, which effec-

tively halves the peak-to-peak output-voltage excur-

sions compared to traditional step-down converters.

See the Load Transient Response graph in the Typical

Operating Characteristics section.

6 _______________________________________________________________________________________

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