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參數(shù)資料
| 型號(hào)： | NCP1521ASNT1G |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.5 MHz, 600 mA, High−Efficiency, Low Quiescent Current, Adjustable Output Voltage Step−Down Converter |
| 中文描述： | 1.2 A SWITCHING REGULATOR, 1800 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | LEAD FREE, TSOP-5 |
| 文件頁(yè)數(shù)： | 8/17頁(yè) |
| 文件大小： | 166K |
| 代理商： | NCP1521ASNT1G |
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NCP1521
http://onsemi.com
8
OPERATION DESCRIPTION
Overview
The NCP1521 uses a constant frequency, current mode
stepdown architecture. Both the main (PChannel
MOSFET) and synchronous (NChannel MOSFET)
switches are internal.
It delivers a constant voltage from either a single LiIon
or three cell NiMH/NiCd battery to portable devices such
as cell phones and PDA. The output voltage is set by the
external resistor divider. The NCP1521 sources at least
600 mA, depending on external components chosen.
The NCP1521 works with two modes of operation;
PWM/PFM depending on the current required. The device
operates in PWM mode at load currents of approximately
40 mA or higher, having voltage tolerance of
90% efficiency or better. Lighter load currents cause the
device to automatically switch into PFM mode for reduced
current consumption (I
Q
= 30 A typ) and extended battery
life.
Additional features include softstart, undervoltage
protection, current overload protection, and thermal
shutdown protection. As shown in Figure 1, only six
external components are required for implementation. The
part uses an internal reference voltage of 0.6 V. It is
recommended to keep the part in shutdown until the input
voltage is 2.7 V or higher.
3% with
PWM Operating Mode
In this mode, the output voltage of the NCP1521 is
regulated by modulating the ontime pulse width of the
main switch Q1 at a fixed frequency of 1.5 MHz. The
switching of the PMOS Q1 is controlled by a flipflop
driven by the internal oscillator and a comparator that
compares the error signal from an error amplifier with the
sum of the sensed current signal and compensation ramp.
At the beginning of each cycle, the main switch Q1 is
turned ON by the rising edge of the internal oscillator
clock. The inductor current ramps up until the sum of the
current sense signal and compensation ramp becomes
higher than the error voltage amplifier. Once this has
occurred, the PWM comparator resets the flipflop, Q1 is
turned OFF and the synchronous switch Q2 is turned ON.
Q2 replaces the external Schottky diode to reduce the
conduction loss and improve the efficiency. To avoid
overall power loss, a certain amount of dead time is
introduced to ensure Q1 is completely turned OFF before
Q2 is being turned ON.
Figure 25. PWM Switching Waveform
(V
in
= 3.6 V, V
out
= 1.8 V, I
out
= 300 mA)
125 ns/div
PFM Operating Mode
Under light load conditions (<40 mA), the NCP1521
enters in low current PFM mode operation to reduce power
consumption. The output regulation is implemented by
pulse frequency modulation. If the output voltage drops
below the threshold of PFM comparator (typically
Vnom2%), a new cycle will be initiated by the PFM
comparator to turn on the switch Q1. Q1 remains ON until
the peak inductor current reaches 200 mA (nom). Then
I
LIM
comparator goes high to switch off Q1. After a short
dead time delay, switch rectifier Q2 is turned ON. The
negative current detector (NCD) will detect when the
inductor current drops below zero and sends the signal to
turn off Q2. The output voltage continues to decrease
through discharging the output capacitor. When the output
voltage falls below the threshold of the PFM comparator,
a new cycle starts immediately.
Figure 26. PFM Mode Switching Waveform
(V
in
= 3.6 V, V
out
= 1.8 V, I
out
= 30 mA)
2.5 s/div
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| NCP1521B | 制造商:ON 功能描述:1.5 MHz, 600 mA Step-Down DC-DC Converter |
| NCP1521BEVB | 功能描述:電源管理IC開發(fā)工具 NCP1521B ANA EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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| NCP1521UEVB | 功能描述:電源管理IC開發(fā)工具 ANA EVAL BRD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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