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| 型號： | MC33166 |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 抗輻射高效，5安培開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 6/16頁 |
| 文件大小： | 403K |
| 代理商： | MC33166 |
MC34166 MC33166
INTRODUCTION
6
MOTOROLA ANALOG IC DEVICE DATA
The MC34166, MC33166 series are monolithic power
switching regulators that are optimized for dc–to–dc converter
applications. These devices operate as fixed frequency,
voltage mode regulators containing all the active functions
required to directly implement step–down and
voltage–inverting converters with a minimum number of
external components. They can also be used cost effectively
in step–up converter applications. Potential markets include
automotive, computer, industrial, and cost sensitive consumer
products. A description of each section of the device is given
below with the representative block diagram shown in
Figure 13.
Oscillator
The oscillator frequency is internally programmed to
72 kHz by capacitor CT and a trimmed current source. The
charge to discharge ratio is controlled to yield a 95%
maximum duty cycle at the Switch Output. During the
discharge of CT, the oscillator generates an internal blanking
pulse that holds the inverting input of the AND gate high,
disabling the output switch transistor. The nominal oscillator
peak and valley thresholds are 4.1 V and 2.3 V respectively.
Pulse Width Modulator
The Pulse Width Modulator consists of a comparator with
the oscillator ramp voltage applied to the noninverting input,
while the error amplifier output is applied into the inverting
input. Output switch conduction is initiated when CT is
discharged to the oscillator valley voltage. As CT charges to
a voltage that exceeds the error amplifier output, the latch
resets, terminating output transistor conduction for the
duration of the oscillator ramp–up period. This PWM/Latch
combination prevents multiple output pulses during a given
oscillator clock cycle. Figures 6 and 14 illustrate the switch
output duty cycle versus the compensation voltage.
Current Sense
The MC34166 series utilizes cycle–by–cycle current
limiting as a means of protecting the output switch transistor
from overstress. Each on–cycle is treated as a separate
situation. Current limiting is implemented by monitoring the
output switch transistor current buildup during conduction, and
upon sensing an overcurrent condition, immediately turning off
the switch for the duration of the oscillator ramp–up period.
The collector current is converted to a voltage by an
internal trimmed resistor and compared against a reference
by the Current Sense comparator. When the current limit
threshold is reached, the comparator resets the PWM latch.
The current limit threshold is typically set at 4.3 A. Figure 9
illustrates switch output current limit threshold versus
temperature.
Error Amplifier and Reference
A high gain Error Amplifier is provided with access to the
inverting input and output. This amplifier features a typical dc
voltage gain of 80 dB, and a unity gain bandwidth of
600 kHz with 70 degrees of phase margin (Figure 3). The
noninverting input is biased to the internal 5.05 V reference
and is not pinned out. The reference has an accuracy of
±
2.0% at room temperature. To provide 5.0 V at the load, the
reference is programmed 50 mV above 5.0 V to compensate
for a 1.0% voltage drop in the cable and connector from the
converter output. If the converter design requires an output
voltage greater than 5.05 V, resistor R1 must be added to
form a divider network at the feedback input as shown in
Figures 13 and 18. The equation for determining the output
voltage with the divider network is:
Vout
R2
R1
1
5.05
External loop compensation is required for converter
stability. A simple low–pass filter is formed by connecting a
resistor (R2) from the regulated output to the inverting input,
and a series resistor–capacitor (RF, CF) between Pins 1 and
5. The compensation network component values shown in
each of the applications circuits were selected to provide
stability over the tested operating conditions. The step–down
converter (Figure 18) is the easiest to compensate for
stability. The step–up (Figure 20) and voltage–inverting
(Figure 22) configurations operate as continuous conduction
flyback converters, and are more difficult to compensate. The
simplest way to optimize the compensation network is to
observe the response of the output voltage to a step load
change, while adjusting RF and CF for critical damping. The
final circuit should be verified for stability under four boundary
conditions. These conditions are minimum and maximum
input voltages, with minimum and maximum loads.
By clamping the voltage on the error amplifier output
(Pin 5) to less than 150 mV, the internal circuitry will be
placed into a low power standby mode, reducing the power
supply current to 36
μ
A with a 12 V supply voltage. Figure 10
illustrates the standby supply current versus supply voltage.
The Error Amplifier output has a 100
μ
A current source
pull–up that can be used to implement soft–start. Figure 17
shows the current source charging capacitor CSS through a
series diode. The diode disconnects CSS from the feedback
loop when the 1.0 M resistor charges it above the operating
range of Pin 5.
Switch Output
The output transistor is designed to switch a maximum of
40 V, with a minimum peak collector current of 3.3 A. When
configured for step–down or voltage–inverting applications,
as in Figures 18 and 22, the inductor will forward bias the
output rectifier when the switch turns off. Rectifiers with a
high forward voltage drop or long turn–on delay time should
not be used. If the emitter is allowed to go sufficiently
negative, collector current will flow, causing additional device
heating and reduced conversion efficiency. Figure 8 shows
that by clamping the emitter to 0.5 V, the collector current will
be in the range of 100
μ
A over temperature. A 1N5822 or
equivalent Schottky barrier rectifier is recommended to fulfill
these requirements.
Undervoltage Lockout
An Undervoltage Lockout comparator has been
incorporated to guarantee that the integrated circuit is fully
functional before the output stage is enabled. The internal
5.05 V reference is monitored by the comparator which
enables the output stage when VCC exceeds 5.9 V. To
prevent erratic output switching as the threshold is crossed,
0.9 V of hysteresis is provided.
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相關(guān)代理商/技術(shù)參數(shù) |
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| MC33166 | 制造商:SPC Multicomp 功能描述:PTC Resettable Fuse |
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| MC33166D2T | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 40V 3A RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| MC33166D2TG | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 40V 3A Buck/Boost/Inverting RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| MC33166D2TR4 | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 40V 3A RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
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