參數(shù)資料
型號(hào)： L5989D
廠商： STMICROELECTRONICS
元件分類： 穩(wěn)壓器
英文描述： 5.06 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封裝： ROHS COMPLIANT, HTSSOP-16
文件頁(yè)數(shù)： 7/51頁(yè)
文件大?。?/td> 1947K
代理商： L5989D
L5989D
Functional description
Doc ID 15778 Rev 3
15/51
5.2
Oscillator
The generation of the internal saw-tooth waveform is based on the constant current charge /
discharge of an internal capacitor. The current generator is designed to get a switching
frequency of 400 kHz ± 10% in case the FSW pin is left floating.
The current mirror connected to FSW (see Figure 5) pin acts increasing / decreasing the
value of the internal charging current to adjust the oscillator frequency. Since the internal
circuitry forces the FSW voltage bias at 1.235 V, the user can easily source / sink current in
this pin connecting a pull up resistor to VREF or a pull down to GND respectively.
Figure 5.
Oscillator circuit block diagram
The value of the pull up resistor versus VREF to decrease the oscillator frequency follows
the formula:
In the same way to increase the switching frequency the pull down resistor is selected using
the formula:
Table 10 shows some resistor values to adjust the oscillator frequency
Clock
Generator
Ramp
Generator
Sawtooth
Clock
VREF
Clock
Generator
Ramp
Generator
Sawtooth
Clock
VREF
R
1 KΩ
()
8.5 10
3
400
F
SW KHz
()
–
---------------------------------------------
0.95
+
=
R
2 KΩ
()
18 10
3
F
SW KHz
() 400
–
---------------------------------------------
2.1
–
=
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相關(guān)代理商/技術(shù)參數(shù)
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L5991A 功能描述:電流型 PWM 控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
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