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參數(shù)資料
| 型號(hào)： | MAX683 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 3.3V-Input to Regulated 5V-Output Charge Pumps |
| 中文描述： | 3.3V輸入、穩(wěn)壓輸出5V的電荷泵 |
| 文件頁(yè)數(shù)： | 7/12頁(yè) |
| 文件大?。?/td> | 154K |
| 代理商： | MAX683 |
M
3.3V-Input to Regulated 5V-Output
Charge Pumps
_______________________________________________________________________________________
7
output noise contains well-defined frequency compo-
nents, and the circuit requires much smaller external
capacitors for a given output ripple. However, constant-
frequency mode, due to higher operating current, is
less efficient at light loads than skip mode. Note: For
input voltages above 3.6V, the devices must operate in
constant-frequency mode. Table 1 summarizes the
tradeoffs between the two operating modes.
Frequenc y S elec tion and S hutdown
The
SHDN
pin on the MAX682/MAX683/MAX684 per-
forms a dual function: it shuts down the device and
determines the oscillator frequency. The
SHDN
input
looks like a diode to ground and should be driven
through a resistor.
Driving
SHDN
low places the device in shutdown
mode. This disables all switches, the oscillator, and
control logic. The device typically draws 0.1μA (5μA
max) of supply current in this mode and the output pre-
sents a 50k
impedance to ground. The device exits
shutdown once
SHDN
is forward biased (minimum of
1μA of current). The typical no-load shutdown exit time
is 50μs.
When
SHDN
is pulled high through an external resistor
to V
IN
, the bias current into
SHDN
determines the
charge-pump frequency. To select the frequency, cal-
culate the external resistor value, R
EXT
, using the fol-
lowing formula:
R
EXT
= 45000 (V
IN
- 0.69V) / f
OSC
where R
EXT
is in k
and f
OSC
is in kHz. Program the
frequency in the 50kHz to 2MHz range. This frequency
range corresponds to
SHDN
input currents between
1μA and 50μA. Proper operation of the oscillator is not
guaranteed beyond these limits. Currents lower than
1μA may shut down the device. The forward-biased
diode voltage from the
SHDN
input to GND has a tem-
perature coefficient of -2mV/°C.
Undervoltage Loc kout
The MAX682/MAX683/MAX684 have an undervoltage-
lockout feature that deactivates the devices when the
input voltage falls below 2.25V. Regulation at low input
voltages cannot be maintained. This safety feature
ensures that the device shuts down before the output
voltage falls out of regulation by a considerable amount
(typically 10% with no load). Once deactivated, hys-
teresis holds the device in shutdown until the input volt-
age rises 100mV above the lockout threshold.
Applic ations Information
Capac itor S elec tion
The MAX682/MAX683/MAX684 require only three exter-
nal capacitors (Figure 5). Their values are closely linked
to the output current capacity, oscillator frequency, out-
put noise content, and mode of operation.
Generally, the transfer capacitor (C
X
) will be the small-
est, and the input capacitor (C
IN
) is twice as large as
C
X
. Higher switching frequencies allow the use of
smaller C
X
and C
IN
. The output capacitor (C
OUT
) can
be anywhere from 5-times to 50-times larger than C
X
,
depending on the mode of operation and ripple toler-
ance. In continuous switching mode, smaller output rip-
ple allows smaller C
OUT
. In skip mode, a larger C
OUT
is
required to maintain low output ripple. Tables 2 and 3
show capacitor values recommended for lowest sup-
ply-current operation (skip mode) and smallest size oper-
ation (constant-frequency mode), respectively.
IN
S1
S2
C
IN
C
OUT
C
X
OUT
OSC
N-CHANNEL
Figure 4. Constant-Frequency-Mode Regulation
FEATURE
SKIP MODE
(
SKIP
= LOW)
CONSTANT-
FREQUENCY MODE
(
SKIP
= HIGH)
Best Light-Load
Efficiency
Smallest External
Component Size
Output Ripple
Amplitude and
Frequency
Relatively large
amplitude, variable
frequency
Relatively small
amplitude, constant
frequency
Load Regulation
Very Good
Good
Table 1. Tradeoffs Between Operating
Modes
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| MAX6830RDUT+T | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類(lèi)型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| MAX6830RDUT-T | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類(lèi)型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
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