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PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
S-8520/8521 Series
Rev.7.2
Seiko Instruments Inc.
10
5.
100% Duty Cycle
The S-8520/21 Series operates with a maximum duty cycle of 100%. When a B, D, F Series product
not provided with an overload protection circuit is used, the switching transistor can be kept ON to
supply current to the load continually, even in cases where the input voltage falls below the preset
output voltage value. The output voltage delivered under these circumstances is one that results from
subtracting, from the input voltage, the voltage drop caused by the DC resistance of the inductance and
the on-resistance of the switching transistor.
If an A, C, E Series product provided with an overload protection circuit is used, this protection circuit
will function when the 100% duty state has lasted longer than the preset overload detection time
(TPRO), causing the IC to enter intermittent operation mode. Under these conditions, the IC will not be
able to supply current to the load continually, unlike the case described in the preceding paragraph.
Selection of Series Products and Associated External Components
1.
Method for selecting series products
The S-8520/21 Series is classified into 12 types, according to the way the control systems (PWM and
PWM/PFM-Switched), the different oscillation frequencies, and the inclusion or exclusion of an
overload protection circuit are combined one with another. Please select the type that best suits your
needs by taking advantage of the features of each type described below.
Control systems:
Two different control systems are available: PWM control system (S-8520 Series) and PWM/PFM-
switched control system (S-8521 Series).
If particular importance is attached to the operation efficiency while the load is on standby — for
example, in an application where the load current heavily varies from that in standby state as the
load starts operating — a high efficiency will be obtained in standby mode by selecting the
PWM/PFM-switched control system (S-8521 Series).
Moreover, for applications where switching noise poses a serious problem, the PWM control system
(S-8520 Series), in which the switching frequency does not vary with the load current, is preferable
because it can eliminate ripple voltages easily using a filter.
Oscillation frequencies:
Three oscillation frequencies--180 kHz (A & B Series) and 60 kHz (C & D Series), 300 kHz (E, F
Series)--are available.
Because of their high oscillation frequency and low-ripple voltage the A, B, E, F Series offer
excellent transient response characteristics. The products in these series allow the use of small-
sized inductors since the peak current remains smaller in the same load current than with products
of the other series. In addition, they can also be used with small output capacitors. These
outstanding features make the A & B Series ideal products for downsizing the associated equipment.
On the other hand, the C & D Series, having a lower oscillation frequency, are characterized by a
small self-consumption of current and excellent efficiency under light loads. In particular, the D
Series, which employs a PWM/PFM-switched control system, enables the operation efficiency to be
improved drastically when the output load current is approximately 100
μ
A. (See Reference Data.)
Overload protection circuit:
Products can be chosen either with an overload protection circuit (A, C, E Series) or without one (B,
D, F Series).
Products with an overload protection circuit (A, C, E Series) enter intermittent operation mode when
the overload protection circuit operates to accommodate overloads or load short-circuiting. This
protects the switching elements and inductors. Nonetheless, in an application where the load needs
to be fed continually with a current by taking advantage of the 100% duty cycle state, even if the
input voltage falls below the output voltage value, a B, D, F Series product will have to be used.
Choose whichever product best handles the conditions of your application.
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相關(guān)代理商/技術(shù)參數(shù) |
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| S-8520D25MC-BVKT2G | 功能描述:DC/DC 開關(guān)控制器 2.5V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520D27MC-BVM-T2 | 功能描述:DC/DC 開關(guān)控制器 2.7V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520D27MC-BVMT2G | 功能描述:DC/DC 開關(guān)控制器 2.7V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520D28MC-BVN-T2 | 功能描述:DC/DC 開關(guān)控制器 2.8V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520D28MC-BVNT2G | 功能描述:DC/DC 開關(guān)控制器 2.8V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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