TLE6389 datasheet(31/38 Pages) INFINEON

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TLE 6389

Datasheet Rev. 2.1

2007-08-13

7.8

SYNC Input and Frequency Control

The TLE 6389’s internal oscillator is set for a fixed PWM switching frequency of 360kHz

or can be synchronized to an external clock at the SYNC pin. When the internal clock is

used SYNC has to be connected to GND. SYNC is a negative-edge triggered input that

allows synchronization to an external frequency ranging between 270kHz and 530kHz.

When SYNC is clocked by an external signal, the converter operates in PWM mode until

the load current drops below the PWM to PFM threshold. Thereafter the converter

continues operation in PFM mode.

7.9

Shutdown Mode

Connecting ENABLE to GND places the

TLE6389-2 GV in shutdown mode. In

shutdown, the reference, control circuitry, external switching MOSFET, and the oscillator

are turned off and the output falls to 0V. Connect ENABLE to voltages higher than 4.5V

for normal operation. As this input operates analog the voltage applied at this pin should

have a slope of 0.5V/3µs to avoid undefined states within the device.

7.10

Buck converter circuit

A typical choice of external components for the buck converter circuit is given in figure

2 and 3. For basic operation of the buck converter the input capacitors C

IN1, CIN2, the

driver supply capacitor C

BDS, the sense resistor RSENSE, the PMOS device, the catch

diode D1, the inductance L1 and the output capacitor C

OUT are necessary. In addition for

low electromagnetic emission a Pi-filter at the input and/or a small resistor in the path

between GDRV and the gate of the PMOS may be necessary.

7.10.1

Buck inductance (L1) selection in terms of ripple current:

The internal PWM/PFM control loop includes a slope compensation for stable operation

in PWM mode. This slope compensation is optimized for inductance values of 47µH and

Sense resistor values of 47m

Ω for the 5V output voltage versions. When choosing an

inductance different from 47µH the Sense resistor has to be changed also:

Increasing this ratio above 1000

Ω/H may result in sub harmonic oscillations as well-

known for peak current mode regulators without integrated slope compensation.

RSENSE

-------------------

(0,5...1,0

)

×10 Ω

----

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