IR3094M International Rectifier Corp., IR3094M Datasheet - Page 18

• Manufacturer Part Number: IR3094M
• Description: 3 Phase Pwm Controller For Point Of Load
• Manufacturer: International Rectifier Corp.

The current sense amplifier gain of IR3094 decreases with temperature at the rate of 1400 PPM, which
compensates part of the inductor DCR increase. The minimum current sense amplifier gain at the maximum IC
temperature T
R
Output Voltage Droop
In some of the applications, output voltage droop is needed to minimize output voltage deviations during load
transients and reduce power dissipation of the load when it is drawing maximum current.
The voltage at the VDRP pin is an average of three phase Current Sense Amplifiers and represents the sum of the
VREF voltage and the average inductor current of all the phases. The VDRP pin is connected to the FB pin through
the R
power supply loop therefore the current through RDRP is equal to (VDRP-VREF) / R
increases, the VDRP voltage increases accordingly which results in an increase in R
output regulated voltage lower thus making the output voltage reduction proportional to an increase in load current.
The droop impedance or output impedance of the converter can thus be programmed by the resistor R
offset and slope of the converter output impedance are independent of the VREF voltage.
The VDRP pin voltage represents the average current of the converter plus the 0.84V reference voltage. The load
current can be retrieved by subtracting the VREF voltage from the VDRP voltage.
The converter voltage will be lowered by R
is determined by Equation (12)
Lossless Average Inductor Current Sensing
Inductor current can be sensed by connecting a series resistor and a capacitor network in parallel with the inductor
and measuring the voltage across the capacitor. The equation of the sensing network is,
Usually the resistor Rcs and capacitor Ccs are chosen so that the time constant of Rcs and Ccs equals the time
constant of the inductor which is the inductance L over the inductor DCR. If the two time constants match, the
voltage across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense
resistor with the value of R
inductor DC current, but affects the AC component of the inductor current.
OCSET
DRP
Page 18 of 29
can be calculated by the following equation (11).
resistor, see figure 6. The Error Amplifier forces the voltage on the FB pin to equal VREF through the
IC_MAX
is calculated from Equation (10).
G
R
CS
L
_
_
MAX
MIN
R
L
OCSET
v
was used. The mismatch of the time constants does not affect the measurement of
C
(
G
s
R
R
)
CS
DRP
L
_
(
_
ROOM
v
ROOM
I
L
LIMIT
3
(
R
s
)
O
FB
1
1 [
*I
1 [

O,

R

sR
R
3850
L
where R
1
1400
_
L
S
MAX
n
_
C
MAX
S
*
)
R
*
10
10
O
O
G
i
¥
G
L
6
¦
is the required output impedance of the converter. R
CS
6
(
CS
s
_
(
)
_
T
MIN
(
1
MIN
T
L
R

IC
_
MAX
L
/
sR
_
I
MAX

OCSET
S
sL

C
T

S
ROOM
T
ROOM
)]
)]
(12)
(13)
(11)
FB
DRP.
(9)
(10)
current, positioning the
IR3094PBF
As the load current
09/26/05
DRP.
The
DRP