參數(shù)資料
型號(hào)： MAX888ECJ
廠商： MAXIM INTEGRATED PRODUCTS INC
元件分類： 電源管理
英文描述： Wireless and Satellite Handset Power-Management ICs
中文描述： 1-CHANNEL POWER SUPPLY SUPPORT CKT, PQFP32
封裝： 7 X 7 MM, 1.40 MM HEIGHT, TQFP-32
文件頁(yè)數(shù)： 16/20頁(yè)
文件大?。?/td> 257K
代理商： MAX888ECJ
M
Wireless and S atellite Handset
Power-Management ICs
16
______________________________________________________________________________________
For example:
V
REF
= 1.25V
V
THF
= falling threshold = 2.52V
V
HYS
= hysteresis = 0.1V
V
THR
= rising threshold = V
THF
+ V
HYS
= 2.62V
R1 = 619k
(1%)
R2 = 562k
(1%)
R3 = 47.6k
(1%)
Power-On S equenc e
(Inc luding
RESET
and S tart-Up T imers)
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).
ONS T AT 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).
T hermal Overload Protec tion
An internal thermal sensor shuts the MAX886/MAX888
down when the maximum temperature limit is exceeded
(160°C typical).
I
2
C-Compatible S erial Interfac e
Use an I
2
C-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 I
2
C-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 S tate
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.
Applic ations Information
Induc tor S elec tion
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:
(
=
(
where I
PEAK
is the peak inductor current (0.9A) and
f
OSC
is the switching frequency.
For example, for a 6V battery voltage, a desired V
OUT0
is 3.3V, the oscillator frequency is 375kHz, and 15μH is
the minimum inductance required.
Diode S elec tion
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
L
4 V
V
I
f
V
/ V
MIN
(
BATT MAX
OUT0
PEAK
OSC
BATT
OUT0
)
)
)
MAX886
MAX888
μ
C
RESET
ONSTAT
OUT2
ON
OFF
10k
Figure 4. One-Button On/Off Control with ONSTAT
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