參數(shù)資料
型號: L5988D
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 5.6 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封裝: LEAD FREE, HTSSOP-16
文件頁數(shù): 7/52頁
文件大?。?/td> 1858K
代理商: L5988D
L5988D
Functional description
Doc ID 15324 Rev 3
15/52
5.2
Oscillator and synchronization
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
Synchronization
SYNCH
VREF
Clock
Generator
Ramp
Generator
Sawtooth
Clock
Synchronization
SYNCH
VREF
R
1
()
8.5 10
3
400
F
SW KHz
()
---------------------------------------------
0.95
+
=
R
2
()
18 10
3
F
SW KHz
() 400
---------------------------------------------
2.1
=
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