The graphprocessor on this card is fed with 1.3V power supply. The
stabiliser is simple fairly as there are two International Rectifier 7413
(IRF7413 –
PDF datasheet, 224Kb) N-channel
field-effect transistors driven by a Chip Advanced Tech 7522 (CAT7522 –
PDF datasheet, 134Kb) PWM controller located on
the back side of the card. By the way, these IRF7413 are fine transistors
capable of max. 11mΩ at Vds=10V and Id=7.3A.
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Actually, the controller is a CAT7522G. Nothing really serious, a Pb-free
version of a regular CAT7522. The stabiliser's input voltage is +12V smoothed
by one TEAPO 470µF/16V liquid electrolytic capacitor. Output voltage is
passed through a 3.3µH choke and smoothed by two liquid electrolytic
capacitors of low impedance, a TEAPO 1000µF/6.3V and a Nichicon HC
470µF/10V. Not sure about the TEAPO one, but this Nichicon HC is good
enough to deliver max. 30mΩ impedance at 20°C and 1230mArms peak
current at 105°C given 100KHz operating frequency in both cases. There is
no reason to admit that this unlabelled Taiwanese one by TEAPO is any better
than its Japanese colleague by Nichicon. Most likely, it's less expensive and
worse considerably. In general, it's supposed to be as good as of OST RLP
series, so here come figures of max. 78mΩ impedance and 700mArms peak
current. By the way, the stabiliser operates at about 250kHz (240kHz calculated
accordingly to a 51kΩ resistor hooked up to the controller's RT pin,
260kHz measured actually). No doubt that such a pair of capacitors would do the
job just fine in case of linear stabiliser, but pulsed-width designs impose much
higher demands on output capacitors. That's difficult to measure how much
current this RV360 consumes under heavy load, but supposed to be about 6A. If we
want to keep voltage delta at +/- 5% (+/- 65mV), then 130 ÷ 6 =
22mΩ total output capacitors' impedance requirement must be met. Our pair
can do exactly 22mΩ at 100kHz, but don't forget to add about 30% to
account for increased losses on reactive inductance at 250kHz. In a matter of
fact, these two capacitors don't fit the design really well. Peak current is
another question which affects capacitors' lifespan. Of course, this card will
be retired probably before they blow up or dry out, but who knows. However, with
increased voltage and current due to upcoming advanced overclocking they may
fail much sooner. Anyway, the author has replaced both of them with a pair of
excellent liquid electrolytic Rubycon MBZ 2200µF/6.3V capacitors. Each of
them delivers max. 13mΩ impedance and 2550mArms peak current, so they
shouldn't die until the next century arrives. Just a joke, but you should have
got the idea. In addition, they offer 3 times more capacitance combined than the
previous pair, so the graphprocessor must feel really happy with this upgrade.
Just in case, a 470µF/16V capacitor on the input has been replaced with a
1000µF/16V one of the same manufacturer. There are also two 22µF
tantalum capacitors (C323 and C324) installed near the primary output
electrolytes and a 10µF multilayer ceramic capacitor (MLCC) situated
behind the graphprocessor on the back side of the card (C24). All of them are
intended to reduce high-frequency voltage losses, and that's good. Another
10µF MLCC wouldn't hurt for sure, so it has been soldered on the top of
the existing one. Having finished with the major components, let's get straight
to voltmodding of this RV360.
CAT7522 uses a resistor divider to set output voltage, and there is a FB pin
for this purpose. The resistors are located on the other side of the card near
the upper mounting hole.
R356 of 3.0kΩ is a so-called lower resistor because it's placed
between earth and the middle point, and R353 of 1.9kΩ is a so-called
upper resistor because it's located beteween output voltage and the middle
point. CAT7522 tries to maintain 0.8V in the middle point. Hence, output voltage
is set at (1.9 ÷ 3.0) × 0.8 + 0.8 = 1.31V. You have to decide how
much voltage you want and install the resistors accordingly. For instance, any
two identical resistors from 1kΩ to 5kΩ range would give you 1.6V.
A 2.7kΩ upper resitor with the existing 3.0kΩ lower resistor would
deliver 1.52V. A 2.2kΩ upper resistor and a 2.7kΩ lower one —
1.45V. All power to you, don't be afraid of experimenting, just do your
soldering job carefully.