ir3084a International Rectifier Corp., ir3084a Datasheet - Page 26

• Manufacturer Part Number: ir3084a
• Description: Xphase Tm Vr 10/11 Control Ic
• Manufacturer: International Rectifier Corp.

No Load Output Voltage Setting Resistor R
An external resistor, R
output voltage offset, V
However, the converter’s output voltage will be set by the combination of VSETPT plus some contribution from
the VDRP pin. At no load, both pins of the Error Amplifier are at VDAC – VSETPT while the VDRP pin is at
VDAC + V
VDRP pin is at a higher voltage than the FB pin of the Error Amplifier, VDRP will contribute to the no load offset
through the RDRP and RFB resistors. The design approach is to choose a value for the feedback resistor, RFB,
from 100 to 2K and then calculate RDRP and R
The total input offset voltage (V
(V
sense resistors R
Finally, calculate the no-load setpoint resistor using Equation (7) and the droop resistor using Equation (8);
CS_OFST)
Page 26 of 45
VSETPT
V
RVSETPT =
RDRP
CS_TOFST
OS
of the amplifier itself plus that created by the amplifier input bias currents flowing through the current
Where:
Where:
B
A
•G
=
=
CSA
=
V
CS+
Io
=
RFB
=
O_NLOFST
(V
*
V
(A
and R
OS
R
CS_OFST
A
VSETPT
VSETPT
O_NLOFST
L
n
+
⋅
*
I
R
G
n is the number of phases
V
V
Ro is the desired load line resistance
V
I
frequency which is a function of R
VSETPT is calculated by Equation (5).
I
and G
*
O
VSETPT
VSETPT
VSETPT
D
OS_EA
O_NLOFST
CS_TOFST
L
D
B
CSA
G
is the full load output current of the converter
+
is the ESR of the output inductor
CS
−
−
, connected between the VDAC pin and the VSETPT pin is used to set the no load
−
CSA
Io
+
is the gain of the current sense amplifiers
VSETPT
C
C
,
CSA
is the offset voltage of the error amplifier (
(
as shown in Equation (6).
*
CS_TOFST
+
which is the difference between the V
is the current into the VSETPT pin at the switching
I
−
*
CSIN
Ro
V
is the total offset voltage of the current sense amplifiers, see below.
is the desired no load offset voltage below the DAC setting
B
D)
are the input offset and gain of the current sense amplifiers). Because the
+
CS
−
+
C
_
V
∗
TOFST
OS_EA
R
) of the current sense amplifier in the phase IC is the sum of input offset
CS
*
+
VSETPT
) (
G
−
VSETPT
CSA
I
CSIN
+
, Feedback Resistor RFB, and AVP Resistor R
V
to provide the required no load offset voltage.
−
OS_EA
∗
OSC
R
CS
, see Figure 15 on page 23.
−
)
C
D
DAC
=
=
V
V
voltage and output voltage at no load.
CS
O_NLOFST
_
TOFST
−
*
V
G
OS_EA
CSA
+
V
IR3084A
OS_EA
10/30/2006
(5)
(6)
(7)
(8)
DRP