TLF50211EL_15 Datasheet, PDF (20/27 Pages) Marl International Limited – 2.2 MHz Step-Down Regulator 500 mA, 5 V, low quiescent current

TLF50211EL
Oscillator
7
Oscillator
7.1
Description
The oscillator supplies the device with a constant frequency. The power switch will be switched on and off with a
constant frequency f_OSC. The time period T_PWM is derived from this frequency and some safety functions are
synchronized to this frequency.
The oscillator frequency can be set by connecting an external resistor R_FREQ between pin FREQ and GND using
the following table (selected values, for more precise setting please refer to Figure 7 below).
Frequency Setting Resistor
7.1.1 Oscillator frequency
7.1.2 Frequency adjusting resistor
f_osc
R_FREQ
2400 2250 1800 1330 1100 kHz
39
43
56
82
100 kΩ
2,5
2,35
2,2
2,05
1,9
1,75
1,6
1,45
1,3
1,15
1
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
Resistor at Freq pin [kΩ]
Figure 7 Switching Frequency f_OSC versus Frequency setting Resistor R_FREQ.
The turn-on frequency can optionally be set externally via the SYNC pin. In this case the synchronization of the
PWM-on signal refers to the falling edge of the SYNC-pin input signal. In case the synchronization to an external
clock signal is not needed, the SYNC pin should be connected to ground. The frequency setting resistor R_FREQ is
also necessary for SYNC option and must be dimensioned according to the desired synchronization frequency
(the ratio between synchronization and internal frequency has to be less than or equal to 1).
The synchronization function is not available in PFM mode.
Data Sheet
20
Rev. 1.0, 2013-06-19