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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
μ
A
(Fsw=150kHz) and may be varied using an external resistor (R
OSC
) connected between OSC pin and
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/
μ
A.
In particular connecting it to GND the frequency is increased (current is sunk from the pin), while connect-
ing R
OSC
to Vcc=12V the frequency is reduced (current is forced into the pin), according to the following
relationships:
ROSC vs. GND:
f
S
150KHz
R
OSC
ROSC vs. 12V:
Note that forcing 25
μ
A into this pin, the device stops switching because no current is delivered to the os-
cillator.
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 0.8375V 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 on a precise point of the divider. The DAC output is delivered to an amplifier obtaining the V
PROG
volt-
age 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 GND. Programming the "11111x" code (VID5
doesn't matter), the device enters the NOCPU mode: all mosfets are turned OFF.
1.237
--------------
6kHz
μ
A
150kHz
6
R
OSC
K
7
R
OSC
K
(
)
-----------------------------
+
=
+
=
f
S
150KHz
–
R
OSC
------------------------
6kHz
μ
A
150kHz
(
)
-----------------------------
+
=
+
=
0
2000
4000
6000
8000
10000
12000
14000
25
50
75
100
125
150
Frequency (KHz)
R
)
0
100
200
300
400
500
600
700
800
150
250
350
450
550
650
Frequency (KHz)
R
)