ir3088a International Rectifier Corp., ir3088a Datasheet - Page 16

• Manufacturer Part Number: ir3088a
• Description: Xphase Ic With Fault And Overtemp Detect
• Manufacturer: International Rectifier Corp.

IR3088A EXTERNAL COMPONENTS
PWM Ramp Resistor R
PWM ramp is generated by connecting the resistor R
as the capacitor C
the capacitor C
(15). To achieve feed-forward voltage mode control, the resistor R
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
follows.
The bias current flowing out of the non-inverting input of the current sense amplifier creates a voltage drop across
R
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
input and the converter output
If R
than 2 kΩ and therefore a larger C
Over Temperature Setting Resistors R
The threshold voltage of VRHOT comparator is proportional to the die temperature T
the relationship between the die temperature of phase IC and the temperature of the power converter according to
the power loss, PCB layout and airflow etc, and then calculate HOTSET threshold voltage corresponding to the
allowed maximum temperature from Equation (18).
There are two ways to set the over temperature threshold, central setting and local setting. In the central setting,
only one resistor divider is used, and the setting voltage is connected to HOTSET pins of all the phase ICs. To
reduce the influence of noise on the accuracy of over temperature setting, a 0.1uF capacitor should be placed next
to HOTSET pin of each phase IC. In the local setting, a resistor divider per phase is needed, and the setting voltage
is connected to HOTSET pin of each phase. The 0.1uF decoupling capacitor is not necessary. Use VBIAS as the
reference voltage. If R
CS+
CS+,
CS-
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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 of
is not used, R
PWMRMP
PWMRMP
V
R
R
R
R
HOTSET
PWMRMP
HOTSET
CS
CS
CS+
HOTSET1
+
−
CS+
PWMRMP
in the range of 100pF and 470pF, and then calculate the resistor R
=
=
should be chosen so that the offset voltage is small enough. Usually R
R
L
C
2
between PWMRMP and LGND. Choose the desired PWM ramp magnitude V
=
represents the inductor current. If the two time constants are not the same, the AC
CS
=
CS
=
R
. 4
.
+
V
L
+
R
is pre-selected, R
73
IN
HOTSET
V
and Capacitor C
BIAS
*
*
CS+
10
f
SW
−
−
1
3
value is needed.
V
∗
*
*
HOTSET
CS+
V
C
HOTSET1
T
HOTSET
PWMRMP
J
+
and Resistors R
. 1
241
HOTSET2
*
and R
PWMRMP
[ln(
PWMRMP
V
IN
HOTSET2
−
can be calculated as follows.
V
V
O
DAC
L
. Pre-select the capacitor C
CS+
between a voltage source and PWMRMP pin as well
)
CS-
−
and R
ln(
PWMRMP
should be added between the amplifier inverting
V
IN
CS-
−
V
DAC
should be connected to the input of the
−
V
PWMRMP
J
(ºC) of phase IC. Determine
)]
CS+
PWMRMP
(15)
(16)
(17)
(18)
(19)
and calculate R
IR3088A
CS+
CS+
1/15
should be less
from Equation
and capacitor
/05
RAMP
CS+
and
as