IR3081 International Rectifier Corp., IR3081 Datasheet - Page 21

• Manufacturer Part Number: IR3081
• Description: Xphasetm Vr 10 Control Ic
• Manufacturer: International Rectifier Corp.

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 (20).
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
Phase Delay Timing Resistors R
The phase delay of the interleaved multiphase converter is programmed by the resistor divider connected at
RMPIN+ or RMPIN- depending on which slope of the oscillator ramp is used for the phase delay programming of
phase IC, as shown in Figure 3.
If the upslope is used, RMPIN+ pin of the phase IC should be connected to RMPOUT pin of the control IC and
RMPIN- pin should be connected to the resistor divider. When RMPOUT voltage is above the trip voltage at
RMPIN- pin, the PWM latch is set. GATEL becomes low, and GATEH becomes high after the non-overlap time.
If down slope is used, RMPIN- pin of the phase IC should be connected to RMPOUT pin of the control IC and
RMPIN+ pin should be connected to the resistor divider. When RMPOUT voltage is below the trip voltage at
RMPIN- pin, the PWM latch is set. GATEL becomes low, and GATEH becomes high after the non-overlap time.
Use VBIAS voltage as the reference for the resistor divider since the oscillator ramp magnitude from control IC
tracks VBIAS voltage. Try to avoid both edges of the oscillator ramp for better noise immunity. Determine the ratio
of the programming resistors corresponding to the desired switching frequencies and phase numbers. If the resistor
R
Combined Over Temperature and Phase Delay Setting Resistors R
The over temperature setting resistor divider can be combined with the phase delay resistor divider to save one
resistor per phase.
Calculate the HOTSET threshold voltage V
Equation (20). If the over temperature setting voltage is lower than the phase delay setting voltage,
VBIAS*RA
between R
PHASEx1
Page 21 of 39
is pre-selected, the resistor R
PHASEx
PHASEx2
, connect RMPIN+ or RMPIN- pin between R
and R
V
R
R
R
R
HOTSET
HOTSET
PHASEx
PHASEx
PHASEx
HOTSET1
PHASEx3
3
2
2
2
=
=
=
=
=
. 4
V
(
RA
R
is pre-selected, R
RA
V
73
BIAS
HOTSET
V
HOTSET
. Pre-select R
PHASEx
BIAS
1
PHASEx
*
PHASE1
10
−
*
1 (
RA
−
−
1
V
3
−
V
∗
∗
BIAS
PHASEx2
∗
*
PHASEx
∗
HOTSET
RA
V
R
HOTSET1
T
V
R
HOTSET
PHASEx
and R
J
BIAS
PHASEx
PHASEx
∗
+
1 (
. 1
HOTSET
−
−
PHASEx1
241
1
V
1
is determined as:
RA
)
PHASE2
HOTSET2
HOTSET
and R
PHASEx
corresponding to the allowed maximum temperature from
,
* )
HOTSET2
)
can be calculated as follows.
R
PHASEx
1
PHASEx1
PHASE1,
and R
R
PHASEx2,
PHASE2
J
(ºC) of phase IC. Determine
and R
and connect HOTSET pin
(20)
(21)
(22)
(23)
(24)
PHASE3
10/01
IR3081
/04