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參數(shù)資料
| 型號(hào)： | MC33680 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | 0.4W, 75V, 0.3A, SIGNAL DIODE, SOD123 |
| 中文描述： | 雙的DC - DC穩(wěn)壓器的電子記事 |
| 文件頁(yè)數(shù)： | 9/16頁(yè) |
| 文件大?。?/td> | 340K |
| 代理商： | MC33680 |
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MC33680
http://onsemi.com
9
DETAILED OPERATING DESCRIPTION
General
The MC33680 is a dual DC–DC regulator designed for
electronic organizer applications. Both regulators apply
Pulse–Frequency–Modulation (PFM). The main boost
regulator output can be externally adjusted from 2.7V to 5V.
An internal synchronous rectifier is used to ensure high
efficiency (achieve 87%). The auxiliary regulator with a
built–in power transistor can be configured to produce a
wide range of positive voltage (can be used for LCD contrast
voltage). This voltage can be adjusted from +5V to +25V by
an external potentiometer.
The MC33680 has been designed for battery powered
hand–held products. With the low start–up voltage from 1V
and the low quiescent current (typical 35
μ
A), the MC33680
is best suited to operate from 1 to 2 AA/ AAA cell.
Moreover, supervisory functions such as low battery
detection, CPU Power–Good signal, and back–up battery
control, are also included in the chip. It makes the MC33680
the best one–chip power management solution for
applications such as electronic organizers and PDAs.
Pulse Frequency Modulation (PFM)
Both regulators apply PFM. With this switching scheme,
every cycle is started as the feedback voltage is lower than
the internal reference. This is normally performed by
internal comparator. As cycle starts, Low–Side switch (i.e.
M1 in Figure 1) is turned ON for a fixed ON time duration
(namely, Ton) unless current limit comparator senses coil
current has reached its preset limit. In the latter case, M1 is
OFF instantly. So Ton is defined as the maximum ON time
of M1. When M1 is ON, coil current ramps up, so energy is
being stored inside the coil. At the moment just after M1 is
OFF, the Synchronous Rectifier (i.e. M2 in Figure 1) or any
rectification device (such as Schottky Diode of Auxiliary
Regulator) is turned ON to direct coil current to charge up
the output bulk capacitor. Provided that coil current limit is
not reached, every switching cycle delivers fixed amount of
energy to the bulk capacitor. For higher loading, a larger
amount of energy (Charge) is withdrawn from the bulk
capacitor, and a larger amount of Charge is then supplied to
the bulk capacitor to regulate output voltage. This implies
switching frequency is increased; and vice–versa.
Main Regulator
Figure 18 shows the simplified block diagram of Main
Regulator. Notice that precise bias current
Iref
is generated
by a VI converter and external resistor
RIref
, where
Iref
0.5
RIref
(A)
This bias current is used for all internal current bias as well
as setting
VMAIN
value. For the latter application,
Iref
is
doubled and fed as current sink at Pin 1. With external
resistor
RMAINb
tied from Pin1 to Pin32, a constant voltage
level shift is generated in between the two pins. In
close–loop operation, voltage at Pin 1 (i.e. Output feedback
voltage) is needed to be regulated at the internal reference
voltage level, 1.22V. Therefore, the delta voltage across Pin
1 and Pin 32 which can be adjusted by
RMAINb
determines
the Main Output voltage. If the feedback voltage drops
below 1.22V, internal comparator sets switching cycle to
start. So,
VMAIN
can be calculated as follows.
VMAIN
1.22
RMAINb
RIref
(V)
From the above equation, although
VMAIN
can be
adjusted by
RMAINb
and
RIref
ratio, for setting
VMAIN
, it
is suggested, by changing
RMAINb
value with
RIref
kept at
480K. Since changing
RIref
will alter internal bias current
which will affect timing functions of Max ON time (
TON1
)
and Min OFF time (
TOFF1
). Their relationships are as
follows;
TON1
1.7
10–11
RIref (S)
TOFF1
Continuous Conduction Mode and Discontinuous
Conduction Mode
In Figure 19, regulator is operating at Continuous
Conduction Mode. A switching cycle is started as the output
feedback voltage drops below internal voltage reference
VREF. At that instant, the coil current is not yet zero, and it
starts to ramp up for the next cycle. As the coil current ramps
up, loading makes the output voltage to decrease as the
energy supply path to the output bulk capacitor is
disconnected. After Ton elapses, M1 is OFF, M2 is ON,
energy is pumped to the bulk capacitor. Output voltage is
increased as excessive charge is pumped in, then it is
decreased after the coil current drops below the loading.
Notice the abrupt spike of output voltage is due to ESR of the
bulk capacitor. Feedback voltage can be resistor–divided
down or level–shift down from the output voltage. As this
feedback voltage drops below VREF, next switching cycle
starts.
6.4
10–12
RIref (S)
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MC33680FTBR2 | 功能描述:IC REG BST SYNC ADJ 0.2A 32LQFP RoHS:否 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- 類(lèi)型:降壓（降壓） 輸出類(lèi)型:固定 輸出數(shù):1 輸出電壓:3.3V 輸入電壓:4.5 V ~ 24 V PWM 型:- 頻率 - 開(kāi)關(guān):- 電流 - 輸出:125mA 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:SOT-23-6 包裝:Digi-Reel® 供應(yīng)商設(shè)備封裝:SOT-6 其它名稱(chēng):MAX1836EUT33#TG16DKR |
| MC33689DDWB | 功能描述:CAN 接口集成電路 SBCLIN RoHS:否 制造商:Texas Instruments 類(lèi)型:Transceivers 工作電源電壓:5 V 電源電流: 工作溫度范圍:- 40 C to + 85 C 封裝 / 箱體:SOIC-8 封裝:Tube |
| MC33689DDWBR2 | 功能描述:CAN 接口集成電路 SBCLIN RoHS:否 制造商:Texas Instruments 類(lèi)型:Transceivers 工作電源電壓:5 V 電源電流: 工作溫度范圍:- 40 C to + 85 C 封裝 / 箱體:SOIC-8 封裝:Tube |
| MC33689DPEW | 制造商:Freescale Semiconductor 功能描述:SYSTEM BASIS CHIP W/LIN 制造商:Freescale Semiconductor 功能描述:SYSTEM BASIS CHIP W/LIN - Bulk 制造商:Freescale Semiconductor 功能描述:IC SYSTEM BASIS W/LIN 32SOIC |
| MC33689DPEWR2 | 制造商:Freescale Semiconductor 功能描述:SYSTEM BASIS CHIP W/LIN 制造商:Freescale Semiconductor 功能描述:SYSTEM BASIS CHIP W/LIN - Tape and Reel 制造商:Freescale Semiconductor 功能描述:IC SYSTEM BASIS W/LIN 32SOIC |
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