L6712A L6712

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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

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

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

µA.

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

ing relationships:

Forcing 25

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

DIGITAL TO ANALOG CONVERTER AND REFERENCE

The built-in digital to analog converter allows the adjustment of the output voltage from 0.900V to 3.300V

as shown in Figure 2. Different voltages can be reached simply changing the Remote Amplifier Gain that

acts as a resistor divider (See relevant section).

The internal reference is trimmed during production process to have an output voltage accuracy of ±0.9%

and a zero temperature coefficient around 70°C including also error amplifier offset compensation. It is

programmed through the voltage identification (VID) pins. These are inputs of an internal DAC that is re-

alized by means of a series of resistors providing a partition of the internal voltage reference. The VID code

drives a multiplexer that select a voltage on a precise point of the divider (see figure 2). The DAC output

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

SGND.

F

SW

150 KHz

[]

1.237

R

OSC

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

kHz

µA

-----------

150 kHz

[]

7.422 10

6

⋅

R

[]

------------------------------ kHz

[]

+

=

⋅

+

=

F

SW

150 KHz

[]

12 1.237

–

R

OSC

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

–

6

kHz

µA

-----------

150 kHz

[]

6.457 10

7

⋅

R

[]

------------------------------ kHz

[]

–

=

⋅

=

0

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Frequency (kHz)

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25

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Frequency (kHz)