MAX888ECJ(1999) Просмотр технического описания (PDF) - Maxim Integrated

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MAX888ECJ
(Rev.:1999)

Wireless and Satellite Handset Power-Management ICs

Maxim Integrated 

Wireless and Satellite Handset

Power-Management ICs

For example:

VREF = 1.25V

VTHF = falling threshold = 2.52V

VHYS = hysteresis = 0.1V

VTHR = rising threshold = VTHF + VHYS = 2.62V

R1 = 619kΩ (1%)

R2 = 562kΩ (1%)

R3 = 47.6kΩ (1%)

Power-On Sequence

(Including RESET and Start-Up Timers)

Drive ON low to begin the power-up sequence. To reduce

overall system cost and complexity, the MAX886/MAX888

incorporate RESET and start-up timers with the power-on

sequence.

The MAX886/MAX888 turn on the reference when ON

goes low. Once the reference is fully powered up, if the

input voltage exceeds the internal undervoltage-lockout

threshold (UVLOR), Regulator 0 turns on. Once OUT0

is in regulation, OUT2 and OUT4 turn on. Once OUT2 is

in regulation, OUT1 and OUT5 turn on and the 75ms

reset timer begins. RESET remains low from the time

OUT2 is valid until the reset timer times out. After the

reset period expires, a 50ms start-up timer begins. The

MAX886/MAX888 shut down if the external logic or con-

troller fails to drive OFF high before the start-up timer

expires. Drive OFF high to continue operation. Driving

OFF low turns off the IC.

There is no required sequence to power off any regula-

tor after the device has turned on. Regulators can be

powered off selectively by sending the correct code

through the serial interface (Table 1).

MAX886

OUT2

MAX888

10k

RESET

ON

ONSTAT

µC

OFF

Figure 4. One-Button On/Off Control with ONSTAT

ONSTAT Output

ONSTAT is a logic output that follows ON. Connect

ONSTAT to the external logic or controller to sense

when the ON pin has been brought low to request shut-

down. This allows easy implementation of a one-button

on/off control scheme (Figure 4).

Thermal Overload Protection

An internal thermal sensor shuts the MAX886/MAX888

down when the maximum temperature limit is exceeded

(160°C typical).

I2C-Compatible Serial Interface

Use an I2C-compatible serial interface to turn the

MAX886/MAX888 on and off, as well as control each

regulator’s output voltage and program the DC-DC

converter and charge pump’s oscillator frequency. Use

standard I2C-compatible receive-byte commands to

program the IC. This part is always a slave to the bus

master. The chip address is 1001 111.

POR State

The power-on reset state of all the DAC and frequency

registers is 0Fh, except for DAC1 which is 04h. The

power-on reset state of the ONX bits is 1 (Table 1). The

power-on voltage for each regulator is shown in bold in

Tables 2, 3, and 5.

Applications Information

Inductor Selection

The essential parameters for inductor selection are

inductance and current rating. The MAX886/MAX888

operate with a wide range of inductance values. In many

applications, values between 10µH and 68µH take best

advantage of the controller’s high switching frequency.

Calculate the minimum inductance value using the sim-

plified equation:

( ) ( ( ) ) L MIN

=

4 VBATT MAX − VOUT0 

⋅ ⋅ IPEAK fOSC VBATT / VOUT0

where IPEAK is the peak inductor current (0.9A) and

fOSC is the switching frequency.

For example, for a 6V battery voltage, a desired VOUT0

is 3.3V, the oscillator frequency is 375kHz, and 15µH is

the minimum inductance required.

Diode Selection

The MAX886/MAX888’s high switching frequency

demands a high-speed rectifier. Schottky diodes, such

as the 1N5817–1N5822 family or surface-mount

MBR0520L series are recommended. Ultra-high-speed

rectifiers with reverse recovery times around 50ns or

16 ______________________________________________________________________________________

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