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參數(shù)資料
| 型號： | MAX748A |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | 通用總線功能 |
| 英文描述： | Synchronous 4-Bit Up/Down Binary Counters 20-LCCC -55 to 125 |
| 中文描述： | 3.3V、降壓型、電流模式PWM DC-DC轉(zhuǎn)換器 |
| 文件頁數(shù)： | 6/12頁 |
| 文件大小： | 135K |
| 代理商： | MAX748A |
PIN #
8-PIN DIP/SO
16-PIN WIDE SO
(MAX748A)
NAME
FUNCTION
1
2
SHDN
Shutdown—active low. Connect to ground to power down chip; tie to V+ for normal
operation. Output voltage falls to 0V when
SHDN
is low.
2
3
REF
Reference Voltage Output (+1.23V) supplies up to 100μA for external loads.
Bypass to GND with a 0.047μF capacitor.
3
7
SS
Soft-Start. Capacitor between SS and GND provides soft-start and
short-circuit protection.
4
8
CC
Compensation Capacitor Input externally compensates the outer (voltage)
feedback loop. Connect to OUT with a 330pF capacitor.
5
9
OUT
Output-Voltage Sense Input provides regulation feedback sensing.
Connect to +3.3V output.
6
10, 11
GND
Ground*
7
12, 13, 14
LX
Drain of internal P-channel power MOSFET*
Supply Voltage Input. Bypass to GND with 1μF ceramic and large-value
electrolytic capacitor in parallel. The 1μF capacitor must be as close
to the GND and V+ pins as possible.*
8
1,15,16
V+
4, 5, 6
N.C.
No Connect—no internal connections to these pins.
_________________Detailed Desc ription
The MAX748A/MAX763A switch-mode regulators use a
current-mode pulse-width-modulation (PWM) control
system in a step-down (buck) regulator topography.
They convert an unregulated DC input voltage from 4V
to 11V (MAX763A) or from 4V to 16V (MAX748A) to a
regulated 3.3V output at 300mA. For loads less than
300mA, V+ may be less than 4.0V (see the Output
Voltage vs. Supply Voltage graph in the Typical
Operating C haracteristics). The current-mode
PWM architecture provides cycle-by-cycle current limit-
ing, improved load-transient response, and simpler
outerloop design.
The controller consists of two feedback loops: an inner
(current) loop that monitors the switch current via the
current-sense resistor and amplifier, and an outer (volt-
age) loop that monitors the output voltage through the
error amplifier (Figure 1). The inner loop performs
cycle-by-cycle current limiting, truncating the power
transistor on-time when the switch current reaches a
predetermined threshold. This threshold is determined
by the outer loop. For example, a sagging output volt-
age produces an error signal that raises the threshold,
allowing the circuit to store and transfer more energy
during each cycle.
Programmable S oft-S tart
Figure 2 shows a capacitor connected to the soft-start
(SS) pin to ensure orderly power-up. A typical value is
0.047μF. SS controls both the SS timing and the maxi-
mum output current that can be delivered while main-
taining regulation.
The charging capacitor slowly raises the clamp on the
error-amplifier output voltage, limiting surge currents
at power-up by slowly increasing the cycle-by-cycle
current-limit threshold. Table 1 lists timing characteris-
tics for selected capacitor values and circuit conditions.
The overcurrent comparator trips when the load exceeds
approximately 1.2A. When either an undervoltage or over-
current fault condition is detected, an SS cycle is actively
initiated, which triggers an internal transistor to discharge
the SS capacitor to ground. An SS cycle is also enabled
at power-up and when coming out of shutdown mode.
Overc urrent Limiting
The overcurrent comparator triggers when the load
current exceeds approximately 1.2A. On each clock
cycle, the output FET turns on and attempts to deliver
current until cycle-by-cycle or overcurrent limits are
exceeded. Note that the SS capacitor must be greater
than 0.01μF for overcurrent protection to function prop-
erly. A typical value is 0.047μF.
M
3.3V, S tep-Down,
Current-Mode PWM DC-DC Converters
6
_______________________________________________________________________________________
_______________________________________________________________________Pin Desc ription
*16-pin wide SO package: All pins sharing the same name must be connected together externally.
相關(guān)PDF資料 |
PDF描述 |
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| MAX748AEWE | Circular Connector; No. of Contacts:26; Series:MS27467; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:17; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:17-26 RoHS Compliant: No |
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| MAX763AEPA | 3.3V, Step-Down, Current-Mode PWM DC-DC Converters |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX748AC/D | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 1.7mA Quiescent Current-Mode PWM DC-DC Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX748AC/D DIE | 制造商:Maxim Integrated Products 功能描述: |
| MAX748ACPA | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 3.3V Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX748ACPA+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 3.3V Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX748ACWE | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 3.3V Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
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