![](http://datasheet.mmic.net.cn/370000/L6712A_datasheet_16703491/L6712A_8.png)
L6712A L6712
8/27
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
μ
A
(Fsw=150kHz) and may be varied using an external resistor (R
OSC
) connected between OSC pin and
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/
μ
A.
In particular connecting it to SGND the frequency is increased (current is sunk from the pin), while con-
necting R
OSC
to Vcc=12V the frequency is reduced (current is forced into the pin), according to the follow-
ing relationships:
R
OSC
vs. GND:
R
OSC
vs. 12V:
Forcing 25
μ
A into this pin, the device stops switching because no current is delivered to the oscillator
Figure 1. R
OSC
vs. Switching Frequency
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
is delivered to an amplifier obtaining the V
PROG
voltage reference (i.e. the set-point of the error amplifier).
Internal pull-ups are provided (realized with a 5
μ
A 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
]
R
OSC
---------------
6kHz
μ
A
150 kHz
]
6
R
OSC
K
[
]
-----------------------------
kHz
[
]
+
=
+
=
F
SW
150 KHz
]
R
OSC
–
------------------------
–
6kHz
μ
A
150 kHz
]
7
R
OSC
K
[
]
-----------------------------
kHz
[
]
–
=
=
0
100
200
300
400
500
600
700
800
150
250
350
450
550
650
Frequency (kHz)
R
)
0
2000
4000
6000
8000
10000
12000
14000
25
50
75
100
125
150
Frequency (kHz)
R
)