參數(shù)資料
型號(hào)： MC34167
廠商： ON SEMICONDUCTOR
元件分類(lèi)： 基準(zhǔn)電壓源/電流源
英文描述： 500kHz and 1MHz High Efficiency 1.5A Switching Regulators; Package: SO; No of Pins: 8; Temperature Range: -40?°C to 85?°C
中文描述： 射頻放大器
文件頁(yè)數(shù)： 7/20頁(yè)
文件大小： 263K
代理商： MC34167
MC34167, MC33167
http://onsemi.com
7
INTRODUCTION
The MC34167, MC33167 series are monolithic power
switching regulators that are optimized for dctodc
converter applications. These devices operate as fixed
frequency, voltage mode regulators containing all the active
functions required to directly implement stepdown and
voltageinverting converters with a minimum number of
external components. They can also be used cost effectively
in stepup 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 14.
Oscillator
The oscillator frequency is internally programmed to
72 kHz by capacitor C
T
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 C
T
, 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 C
T
is
discharged to the oscillator valley voltage. As C
T
charges to
a voltage that exceeds the error amplifier output, the latch
resets, terminating output transistor conduction for the
duration of the oscillator rampup period. This PWM/Latch
combination prevents multiple output pulses during a given
oscillator clock cycle. Figures 7 and 15 illustrate the switch
output duty cycle versus the compensation voltage.
Current Sense
The MC34167 series utilizes cyclebycycle 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
rampup 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 6.5 A.
Figure 10 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 4). 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 R
1
must be added to form a divider network at the feedback
input as shown in Figures 14 and 19. The equation for
determining the output voltage with the divider network is:
Vout
5.05
R2
R1
1
External loop compensation is required for converter
stability. A simple lowpass filter is formed by connecting
a resistor (R
2
) from the regulated output to the inverting
input, and a series resistorcapacitor (R
F
, C
F
) 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
stepdown converter (Figure 19) is the easiest to
compensate for stability. The stepup (Figure 21) and
voltageinverting (Figure 23) 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 R
F
and
C
F
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 A with a 12 V supply voltage.
Figure 11 illustrates the standby supply current versus
supply voltage.
The Error Amplifier output has a 100 A current source
pullup that can be used to implement softstart. Figure 18
shows the current source charging capacitor C
SS
through a
series diode. The diode disconnects C
SS
from the feedback
loop when the 1.0 M resistor charges it above the operating
range of Pin 5.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MC34167_05 制造商:ONSEMI 制造商全稱(chēng):ON Semiconductor 功能描述:5.0 A, Step−Up/Down/Inverting Switching Regulators
MC34167D2T 功能描述:直流/直流開(kāi)關(guān)調(diào)節(jié)器 40V 5A RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開(kāi)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
MC34167D2TG 功能描述:直流/直流開(kāi)關(guān)調(diào)節(jié)器 40V 5A Buck/Boost/Inverting RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開(kāi)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
MC34167D2TR4 功能描述:直流/直流開(kāi)關(guān)調(diào)節(jié)器 40V 5A RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開(kāi)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
MC34167D2TR4G 功能描述:直流/直流開(kāi)關(guān)調(diào)節(jié)器 40V 5A Buck/Boost/Inverting RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開(kāi)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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