MAX886(1999) Просмотр технического описания (PDF) - Maxim Integrated

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MAX886
(Rev.:1999)

Wireless and Satellite Handset Power-Management ICs

Maxim Integrated 

Wireless and Satellite Handset

Power-Management ICs

The serial interface programs VOUT0 from 2.625V to

3.75V in 75mV steps for the MAX886 (Tables 1 and 2),

or from 1.527V to 3.027V in 100mV steps for the

MAX888 (Tables 1 and 3).

Regulator 0 operates in one of four preset frequencies,

from 375kHz to 925kHz, programmable through the

serial interface (Table 4).

For the device to power up properly, VIN0 must be high

enough for REG0 to get into regulation. For the MAX886,

Regulator 0’s default voltage is 3.75V. Since the rest of

the regulators do not power up until Regulator 0 is

ready, VIN0 must be greater than approximately 4V for

the device to power up properly. The Regulator 0 default

voltage for the MAX888 is 2.027V, so the minimum VIN0

required to start up is limited by the minimum operating

voltage range (2.7V). After power-up, the device oper-

ates until VBATT drops below VUVLOF (undervoltage

lockout falling threshold).

Sync Mode

The SYNC input allows the MAX886/MAX888 to syn-

chronize with an external clock applied to SYNC, ensur-

ing that switching harmonics are kept away from

sensitive IF bands. The SYNC detector triggers on

SYNC’s falling edge.

PWM Mode

Regulator 0 is in PWM mode when SYNC is connected to

CVL or driven to a logic-high voltage. Two internal switch-

es operate at a preset frequency even when there is no

load. The P-channel MOSFET turns on to charge the

inductor until the error comparator or current-limit com-

parator turns it off. The N-channel MOSFET then turns on

to discharge the inductor. To prevent the output from

soaring with no load in PWM mode, the N-channel switch

stays on long enough to allow the inductor current to go

negative. Once the N-channel switch turns off, the voltage

at LX rises (rings) until the next cycle when the P-channel

switch turns on again. As the load increases and the

inductor enters continuous conduction, ringing is no

longer present and the LX waveform looks like a square

wave whose duty cycle depends on the input and output

voltages. As the input voltage approaches the same level

as the output voltage, the P-channel switch stays on

100% of the time, providing the lowest possible dropout.

PFM Mode

Regulator 0 operates in PFM mode when SYNC is dri-

ven to a logic low voltage or connected to GND. When

VOUT0 drops below the regulation threshold, the P-

channel switch turns on to charge the inductor until the

error comparator or current-limit comparator turns it off.

At light loads, the N-channel then turns on to discharge

the inductor until the current in the inductor reaches

zero. In PFM mode, the inductor current does not go

negative to discharge the output. At no-load there is a

long period between pulses of inductor current. As the

load current increases, the period between pulses

becomes shorter until the pulses become continuous. At

load currents above this point, Regulator 0 automatically

switches to PWM mode, and the VLX waveform looks like

a square wave whose duty cycle depends on the input

and output voltages. As the input voltage approaches

the same level as the output voltage, the P-channel

switch stays on 100% of the time, providing the lowest

possible dropout. It is typically more efficient to use the

PFM mode when the load current is less than 100mA.

100mA LDO Regulator 1

Regulator 1, a low-dropout linear regulator, sources a

minimum of 100mA and operates from voltages at IN1

of up to 12V. The serial interface programs VOUT1 from

2.7V to 4.95V in 75mV steps for the MAX886 (Tables 1

and 2), or from 1.25V to 3.50V in 150mV steps for the

MAX888 (Tables 1 and 3). IN1 may be powered from

the battery, OUT0, or any other voltage source.

200mA LDO Regulator 2

Regulator 2, a low-dropout linear regulator, sources a

minimum of 200mA. The serial interface programs VOUT2

from 2.175V to 3.3V in 75mV steps for the MAX886 (Tables

1 and 2), or from 1.527V to 3.027V in 100mV steps for the

MAX888 (Tables 1 and 3). IN2 may be powered from the

battery, OUT0, or any other voltage source less than 5.5V.

20mA LDO Regulator 3

Regulator 3, a low-dropout linear regulator, sources a

minimum of 20mA. The serial interface programs VOUT3

to one of four different output voltages: 0V, 2.85V, 4.65V,

or VOUT2 (Tables 1 and 5). Although this is a general-

purpose output, OUT3 is intended for the SIM supply. IN3

may be powered from OUT4 or from any regulated 5V

supply.

When programmed to 0V or VOUT2, OUT3 is either actively

discharged to GND (for 0V mode) or connected to OUT2

(for VOUT2), and Regulator 3 is disabled to conserve

power.

100mA Charge-Pump Regulator 4

Regulator 4, a regulated charge pump, generates 5.25V

and delivers up to 100mA. An oscillator synchronized to the

PWM clock regulates OUT4 to minimize noise. It operates

at one-half the frequency of the PWM oscillator to ensure

50% duty-cycle outputs. IN4 may be powered from the bat-

tery, OUT0, or any other voltage source less than 5.5V.

To save space and cost, use a small ceramic flying

capacitor. See Table 6 for recommended flying capaci-

tor values.

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