TLD5098EL Datasheet, PDF (13/39 Pages) Infineon Technologies AG – DC/DC Boost, Buck-Boost, SEPIC controller

TLD5098EL
Oscillator and Synchronization
6
Oscillator and Synchronization
6.1
Description
The internal oscillator is used to determine the switching frequency of the boost regulator. The switching frequency
can be selected from 100 kHz to 500 kHz with an external resistor to GND. To set the switching frequency with an
external resistor the following formula can be applied.
( ) ( ) ^{( )} [ ] [ ] ^{[ ] [ ] R FREQ}
=
1
141 × 10 ^−12
s
Ω
×
f _FREQ
1
s
− 3 .5 × 10 ³ Ω
Ω
In addition, the oscillator is capable of changing from the frequency set by the external resistor to a synchronized
frequency from an external clock source. If an external clock source is provided on the pin FREQ/SYNC, then the
internal oscillator synchronizes to this external clock frequency and the boost regulator switches at the
synchronized frequency. The synchronization frequency capture range is 250 kHz to 500 kHz.
FREQ / SYNC
11
V_CLK
R_FREQ
Oscillator
Clock Frequency
Detector
Multiplexer
PWM
Logic
Gate
Driver
2 SWO
Figure 4 Oscillator and Synchronization Block Diagram and Simplified Application Circuit
V_SYNC
t_SYNC,TR
t_SYNC,TR
T_SYNC = 1 / f_SYNC
t_SYNC,PWH
4.5 V
V_SYNC,H
V_SYNC,L
0.5 V
t
Figure 5 Synchronization Timing Diagram
Datasheet
13
Rev. 1.0, 2010-10-13