MAX8582ETB(2006) 查看數據表（PDF） - Maxim Integrated

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MAX8582ETB
(Rev.:2006)

2.5MHz/1.5MHz Step-Down Converters with 60mΩ Bypass in TDFN for CDMA PA Power

Maxim Integrated 

2.5MHz/1.5MHz Step-Down Converters

with 60mΩ Bypass in TDFN for CDMA PA Power

Pin Description

PIN

NAME

1

GND

Ground

FUNCTION

2, 3

IN

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

and GND.

4

SHDN

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

logic-low for shutdown mode.

5

HP

High-Power Mode Set Input. Drive HP high to invoke bypass mode. Bypass mode connects IN

directly to OUT with the internal bypass MOSFET.

6

REFIN

DAC-Controlled Input. Output regulates to 2 x VREFIN for the MAX8581 and MAX8582. Dual-mode

threshold at 0.465 VIN enables bypass mode.

7

IC

Internally Connected. Connect to ground.

8, 9

OUT

Output Voltage Connection for Bypass Mode. Internally connected to IN using the internal bypass

MOSFET during bypass mode. Connects to the internal feedback network.

10

LX

Inductor Connection. Connect inductor to the drains of the internal p-channel and n-channel

MOSFETs. Connects to the internal feedback network.

—

EP

Exposed Paddle. Connect to GND.

Detailed Description

The MAX8581/MAX8582 step-down converters deliver

over 600mA to dynamically power the PA in CDMA

handsets. The hysteretic PWM control scheme switches

with nearly fixed frequency at 1.5MHz (MAX8582) to

2.5MHz (MAX8581), allowing efficiency and tiny external

components. A 60mΩ bypass mode connects the PA

directly to the battery during high-power transmission.

Control Scheme

A hysteretic PWM control scheme ensures high effi-

ciency, fast switching, fast transient response, low out-

put ripple, and physically tiny external components.

This control scheme is simple: When the output voltage

is below the regulation voltage, the error comparator

begins a switching cycle by turning on the high-side

switch. This switch remains on until the minimum on-

time expires and the output voltage is in regulation 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 out of regulation.

During this period, the low-side synchronous rectifier

turns on and remains on until the high-side switch turns

on again. The internal synchronous rectifier eliminates

the need for an external Schottky diode.

Voltage-Positioning Load Regulation

The MAX8581/MAX8582 utilize a unique feedback net-

work. By taking feedback from the LX node, the usual

phase lag due to the output capacitor is removed, mak-

ing the loop exceedingly stable and allowing the use of

very small ceramic output capacitors. This configura-

tion yields load regulation equal to half the inductor’s

series resistance multiplied by the load current. This

voltage-positioning load regulation greatly reduces

overshoot during load transients or when changing

VOUT from one voltage to another. However, when cal-

culating REFIN voltage, the load regulation should be

considered. Because inductor resistance is typically

well specified and the typical PA is a resistive load, the

VREFIN to VOUT gain is slightly less than 2V/V for the

MAX8581/MAX8582.

Bypass Mode

During high-power transmission, the bypass mode’s

low on-resistance provides low dropout, long battery

life, and high output-current capability. Bypass mode

connects IN directly to OUT with the internal 60mΩ

(typ) bypass FET, while the step-down converter is

forced into 100% duty-cycle operation to slightly lower

total on-resistance to less than 60mΩ (typ).

6 _______________________________________________________________________________________

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