ir3084u International Rectifier Corp., ir3084u Datasheet - Page 31

• Manufacturer Part Number: ir3084u
• Description: Xphasetm Vr10, Vr11 & Opteron/athlon64 Control Ic
• Manufacturer: International Rectifier Corp.

IR3086 EXTERNAL COMPONENTS
PWM Ramp Resistor R
PWM ramp is generated by connecting the resistor R
well as the capacitor C
V
from Equation (18). To achieve feed−forward voltage mode control, the resistor R
the input of the converter.
Inductor Current Sensing Capacitor C
The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor R
C
across the capacitor C
component of the capacitor voltage is different from that of the real inductor current. The time constant mismatch
does not affect the average current sharing among the multiple phases, but affect the current signal ISHARE as
well as the output voltage during the load current transient if adaptive voltage positioning is adopted.
Measure the inductance L and the inductor DC resistance R
as follows.
The bias current flowing out of the non-inverting input of the current sense amplifier creates a voltage drop across
R
of converter current signal ISHARE as well as the accuracy of the converter output voltage if adaptive voltage
positioning is adopted. To reduce the offset voltage, a resistor R
inverting input and the converter output
non-inverting input and the bias current from the inverting input.
If R
less than 2 kΩ and therefore a larger C
R
RAMP
CS+
CS+,
PWMRMP
CS−
in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage
which is equivalent to an input offset voltage of the current sense amplifier. The offset affects the accuracy
and the capacitor C
is not used, R
Page 31 of 47
R
R
CS
CS
+
−
=
=
=
I
I
L
C
V
CSIN
CSIN
IN
CS
R
+
L
*f
+
−
CS+
CS+
∗
SW
PWMRMP
PWMRMP
R
should be chosen so that the offset voltage is small enough. Usually R
CS
PWMRMP
represents the inductor current. If the two time constants are not the same, the AC
*C
+
PWMRMP
and Capacitor C
between PWMRMP and LGND. Choose the desired PWM ramp magnitude
in the range of 100pF and 470pF, and then calculate the resistor R
CS+
.
CS+
The resistor R
*[ln(V
value is needed.
and Resistors R
IN
PWMRMP
−
PWMRMP
CS−
V
DAC
V
is determined by the ratio of the bias current from the
O
L
. Pre−select the capacitor C
CS+
)
between a voltage source and PWMRMP pin as
−
and R
ln(V
CS−
IN
CS−
should be added between the amplifier
−
V
DAC
RAMP
−
V
PWMRMP
should be connected to
CS+
and calculate R
IR3084U
CS+
(19)
(20)
CS+
9/14/2005
and capacitor
)]
should be
PWMRMP
(18)
CS+