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参数资料
| 型号： | MAX1901-MAX1904 |
| 厂商： | Maxim Integrated Products, Inc. |
| 英文描述： | 3 POSITION RIGHT ANGLE DIP SWITCH |
| 中文描述： | 500kHz的多路输出，低噪声电源用于笔记本电脑控制器 |
| 文件页数： | 18/33页 |
| 文件大小： | 649K |
| 代理商： | MAX1901-MAX1904 |
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M
500kHz Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
18
______________________________________________________________________________________
RESET
Power-Good Voltage Monitor
The power-good monitor generates a system
RESET
signal. At first power-up,
RESET
is held low until both
the 3.3V and 5V SMPS outputs are in regulation. At this
point, an internal timer begins counting oscillator puls-
es, and
RESET
continues to be held low until 32,000
cycles have elapsed. After this timeout period (64ms at
500kHz or 96ms at 333kHz),
RESET
is actively pulled
up to V
L
. If SEQ is tied to REF (for separate ON3/ON5
controls), only the 3.3V SMPS is monitored
—
the 5V
SMPS is ignored.
Output Undervoltage Shutdown
Protection (MAX1901/MAX1902)
The output undervoltage lockout circuit is similar to
foldback current limiting, but employs a timer rather
than a variable current limit. Each SMPS has an under-
voltage protection circuit that is activated 6144 clock
cycles after the SMPS is enabled. If either SMPS output
is under 70% of the nominal value, both SMPSs are
latched off and their outputs are clamped to ground by
the synchronous rectifier MOSFETs (see the
Output
Overvoltage Protection
section). They won
’
t restart until
SHDN
or RUN/ON3 is toggled, or until V+ power is
cycled below 1V. Note that undervoltage protection can
make prototype troubleshooting difficult, since you
have only 12ms or 18ms to figure out what might be
wrong with the circuit before both SMPSs are latched
off. In extreme cases, it may be useful to substitute the
MAX1904 into the prototype breadboard until the proto-
type is working properly.
Output Overvoltage Protection
(MAX1901/MAX1902)
Both SMPS outputs are monitored for overvoltage. If
either output is more than 7% above the nominal regu-
lation point, both low-side gate drivers (DL_) are
latched high until
SHDN
or RUN/ON3 is toggled, or
until V+ power is cycled below 1V. This action turns on
the synchronous rectifiers with 100% duty, in turn rapid-
ly discharging the output capacitors and forcing both
SMPS outputs to ground. The DL outputs are also kept
high whenever the corresponding SMPS is disabled,
and in shutdown if V
L
is sustained.
Discharging the output capacitor through the main
inductor causes the output to momentarily go below
GND. Clamp this negative pulse with a back-biased 1A
Schottky diode across the output capacitor (Figure 1).
To ensure overvoltage protection on initial power-up,
connect signal diodes from both output voltages to V
L
(cathodes to V
L
) to eliminate the V
L
power-up delay.
This circuitry protects the load from accidental overvolt-
age caused by a short circuit across the high-side
power MOSFETs. This scheme relies on the presence
of a fuse, in series with the battery, which is blown by
the resulting crowbar current. Note that the overvoltage
circuitry will interfere with external keep-alive supplies
that hold up the outputs (such as lithium backup or hot-
swap power supplies); in such cases, the MAX1904
should be used.
Low-Noise Operation (PWM Mode)
PWM mode (
SKIP
= high) minimizes RF and audio inter-
ference in noise-sensitive applications (such as hi-fi multi-
media-equipped systems), cellular phones, RF
communicating computers, and electromagnetic pen
entry systems. See the summary of operating modes in
Table 2.
SKIP
can be driven from an external logic signal.
Table 4. Operating Modes
SHDN
SEQ
RUN/ON3
TIME/ON5
MODE
DESCRIPTION
Low
X
X
X
Shutdown
All circuit blocks turned off.
Supply current = 4μA.
High
High
High
High
High
High
High
High
REF
REF
REF
REF
GND
GND
VL
VL
Low
High
Low
High
Low
High
Low
High
Low
Low
High
High
Standby
Run
Run
Run
Standby
Run
Standby
Run
Both SMPSs off. Supply current = 30μA.
3.3V SMPS enabled/5V off.
5V SMPS enabled/3.3V off.
Both SMPSs enabled.
Both SMPSs off. Supply current = 30μA.
Both SMPSs enabled. 5V enabled before 3.3V.
Both SMPSs off. Supply current = 30μA.
Both SMPSs enabled. 3.3V enabled Before 5V.
Timing Capacitor
Timing Capacitor
Timing Capacitor
Timing Capacitor
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