MAX888ECJ Maxim, MAX888ECJ Datasheet - Page 13

• Manufacturer Part Number: MAX888ECJ
• Description: Wireless and Satellite Handset Power-Management ICs
• Manufacturer: Maxim

The serial interface programs V
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, V
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, V
the device to power up properly. The Regulator 0 default
voltage for the MAX888 is 2.027V, so the minimum V
required to start up is limited by the minimum operating
voltage range (2.7V). After power-up, the device oper-
ates until V
lockout falling threshold).
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.
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.
Regulator 0 operates in PFM mode when SYNC is dri-
ven to a logic low voltage or connected to GND. When
V
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
OUT0
drops below the regulation threshold, the P-
IN0
BATT
must be greater than approximately 4V for
drops below V
______________________________________________________________________________________
UVLOF
OUT0
IN0
from 2.625V to
(undervoltage
Wireless and Satellite Handset
must be high
Sync Mode
PWM Mode
PFM Mode
IN0
Power-Management ICs
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 V
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.
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 V
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.
Regulator 2, a low-dropout linear regulator, sources a
minimum of 200mA. The serial interface programs V
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.
Regulator 3, a low-dropout linear regulator, sources a
minimum of 20mA. The serial interface programs V
to one of four different output voltages: 0V, 2.85V, 4.65V,
or V
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 V
discharged to GND (for 0V mode) or connected to OUT2
(for V
power.
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.
OUT2
OUT2
(Tables 1 and 5). Although this is a general-
), and Regulator 3 is disabled to conserve
100mA Charge-Pump Regulator 4
100mA LDO Regulator 1
200mA LDO Regulator 2
20mA LDO Regulator 3
OUT2
, OUT3 is either actively
LX
waveform looks like
OUT1
OUT3
OUT2
from
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