9/34

L6710

OSCILLATOR

The switching frequency is internally fixed at 150kHz. Each phase works at the frequency fixed by the os-

cillator so that the resulting switching frequency at the load side results in being doubled.

The internal oscillator generates the triangular waveform for the PWM charging and discharging with a

constant current an internal capacitor. The current delivered to the oscillator is typically 25

µA

GND or Vcc. Since the OSC pin is maintained at fixed voltage (Typ. 1.237V), the frequency is varied pro-

portionally to the current sunk (forced) from (into) the pin considering the internal gain of 6KHz/

µA.

In particular connecting it to GND the frequency is increased (current is sunk from the pin), while connect-

relationships:

ROSC vs. GND:

ROSC vs. 12V:

Note that forcing 25

µA into this pin, the device stops switching because no current is delivered to the os-

cillator.

DIGITAL TO ANALOG CONVERTER AND REFERENCE

The built-in digital to analog converter allows the adjustment of the output voltage from 0.8375V to

1.6000V with 12.5mV as shown in the previous table 1 automatically regulating VID* = VID - 25mV in order

to avoid any external component or circuitry to lower the regulated voltage meeting VRD10 specs. The

internal reference is trimmed to ensure the output voltage precision of ±0.5% and a zero temperature co-

efficient around 70°C. The internal reference voltage for the regulation is programmed by the voltage iden-

tification (VID) pins. These are inputs of an internal DAC that is realized by means of a series of resistors

providing a partition of the internal voltage reference. The VID code drives a multiplexer that selects a volt-

age reference (i.e. the set-point of the error amplifier). Internal pull-ups are provided (realized with a 5

µA

current generator up to 3V Typ); in this way, to program a logic "1" it is enough to leave the pin floating,

while to program a logic "0" it is enough to short the pin to GND. Programming the "11111x" code (VID5

doesn't matter), the device enters the NOCPU mode: all mosfets are turned OFF.

f

S

150 KHz

1.237

R

OSC

--------------- 6

kHz

µA

-----------

150kHz

7.422 10

6

⋅

R

()

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

+

=

⋅

+

=

f

S

150 KHz

12 1.237

–

R

OS C

------------------------- 6

kHz

µA

-----------

150 kHz

6.457 10

7

⋅

R

()

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

+

=

⋅

+

=

0

2000

4000

6000

8000

10000

12000

14000

25

50

75

100

125

150

Frequency (KHz)

0

100

200

300

400

500

600

700

800

150

250

350

450

550

650

Frequency (KHz)