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參數(shù)資料
| 型號(hào)： | S-8340B |
| 廠商： | Seiko Instruments Inc. |
| 英文描述： | PWM Control High-Frequency Step-Up Switching Regulator-Controllers(PWM控制，高頻步升開關(guān)穩(wěn)壓器-控制器) |
| 中文描述： | PWM控制高頻升壓型開關(guān)穩(wěn)壓器控制器（脈寬調(diào)制控制，高頻步升開關(guān)穩(wěn)壓器-控制器） |
| 文件頁數(shù)： | 13/38頁 |
| 文件大?。?/td> | 420K |
| 代理商： | S-8340B |
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PWM Control & PWM/PFM Control High-Frequency Step-Up Switching Regulator-Controllers
S-8340/8341 Series
Rev.1.00
Seiko Instruments Inc.
12
4. Current Limit Circuit
The current limit circuit of the S-8340/41 series can limit current by inserting a sense resistor (RSENSE)
between an external FET source or an external NPN bipolar transistor emitter and Vss and entering a
connection point with a sensor resistor into the SENSE pin to prevent thermal destruction of external
transistors due to overload or magnetic saturation of a coil. (See the standard circuit on pages 18 and
19.)
A current limiting comparator in the IC monitors the SENSE pin reaches the current limit detection
voltage (VSENSE=120 mV (typ.) ). The current flowing into the external transistor is limited by turning
the external transistor off for a clock from the oscillator after detection, the transistor is turned on again
with the ON signal of the next clock, and current limit detection resumes.
However, this current limit circuit contains a CR filter with a time constant of 220 ns (typ.) between the
SENSE pin and the current limiting comparator in the IC to prevent detection errors caused by the spike
voltage that occurs at the SENSE pin. If the time (pulse width ton: Hi time at EXT pin) after the external
transistor turns on until the current limit circuit works is short, the current value that is actually limited
becomes higher than the current limit setting value determined by VSENSE/RSENSE as a side effect.
The actual limit current value I
LIMIT
is expressed by the following equation:
I
VSENSE
RSENSE
1
e
LIMIT
ton 0.5
CR
=
÷
(The CR in this equation is determined by the internal CR filter and varies in the range 116 to 470 ns
(220 ns typ.).)
Therefore, this current limit function does not guarantee full protection of external components by
I
LIMIT
=VSENSE/RSENSE under all operating conditions. We recommend that you evaluate it by testing
performance with the actual equipment.
For example, the current value that actually activates the current limit circuit becomes much higher than
the current limit setting determined by VSENSE/RSENSE when it is used under the condition that the
input voltage is close to the output voltage or when the current limit circuit works and the output voltage
falls and becomes close to the input voltage. Figure 8 gives an example of the actually measured
increase of the peak current flowing through the coil when the current limit circuit works while the input
voltage is becoming close to the output voltage. Figure 9 shows an example of the actually measured
increase of the peak current flowing through the coil when the output voltage drops
and approaches the
input voltage by increasing the output current after the current limit circuit works.
If the current limit circuit is not used, the sensor resistor should be removed and the external transistor
source or emitter and SENSE pin should be connected to V
SS
.
Figure 8
S-8340A50 Rsense=51m
0
1
2
3
4
1
2
3
4
5
V
IN
(V)
ILpeak
(A)
(ILpeak measured when the current limit circuit is
activated (VOUT begins to fall).)
VSENSE / RSENSE
Input voltage - Coil peak current
(Coil peak current ILpeak measured)
Figure 9
S-8340A50 VIN=3V Rsense=51m
Output current - Coil peak current
0
1
2
3
4
5
0
1
2
3
Current limit circuit
is activated
VSENSE / RSENSE
Output current I
OUT
(A)
Coil peak
current Ipk
(A)
Influence of CR
filter
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| S-8341 | PWM/PFM Control High-Frequency Step-Up Switching Regulator-Controllers(PWM/PFM控制，高頻步升開關(guān)穩(wěn)壓器-控制器) |
| S-8341A | PWM/PFM Control High-Frequency Step-Up Switching Regulator-Controllers(PWM/PFM控制，高頻步升開關(guān)穩(wěn)壓器-控制器) |
| S-8341B | PWM/PFM Control High-Frequency Step-Up Switching Regulator-Controllers(PWM/PFM控制，高頻步升開關(guān)穩(wěn)壓器-控制器) |
| S-8420AF | BATTERY BACKUP IC FOR 1-CHIP CPU |
| S-8420BF | BATTERY BACKUP IC FOR 1-CHIP CPU |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| S-8340B00AFT-T2 | 功能描述:DC/DC 開關(guān)控制器 Adj Step-Up 2.0% 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-8340B00AFT-T2-G | 功能描述:DC/DC 開關(guān)控制器 Adj Step-Up 2.0% 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-8340B00AFT-T2-U | 功能描述:IC REG CTRLR BOOST 8TSSOP 制造商:ablic u.s.a. inc. 系列:- 包裝:剪切帶（CT） 零件狀態(tài):在售 輸出類型:晶體管驅(qū)動(dòng)器 功能:升壓 輸出配置:正 拓?fù)?升壓 輸出數(shù):1 輸出階段:1 電壓 - 電源（Vcc/Vdd）:0.8 V ~ 6 V 頻率 - 開關(guān):600kHz 占空比（最大）:0.89 同步整流器:無 時(shí)鐘同步:無 串行接口:- 控制特性:限流，使能，軟啟動(dòng) 工作溫度:-40°C ~ 85°C（TA） 封裝/外殼:8-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商器件封裝:8-TSSOP 標(biāo)準(zhǔn)包裝:1 |
| S-8340C25AFT-T2 | 功能描述:DC/DC 開關(guān)控制器 2.5V Step-Up 2.0% 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-8340C25AFT-T2-G | 功能描述:DC/DC 開關(guān)控制器 2.5V Step-Up 2.0% 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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