IR3094PBF 데이터 시트보기 (PDF) - International Rectifier
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IR3094PBF Datasheet PDF : 29 Pages
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IR3094PBF
RL _ MAX RL _ ROOM [1 3850 *10¥ 6 (TL _ MAX TROOM )]
(9)
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 TIC_MAX is calculated from Equation (10).
GCS _ MIN GCS _ ROOM [1 1400 *10¦ 6 (TIC _ MAX TROOM )]
(10)
ROCSET can be calculated by the following equation (11).
ROCSET
( I LIMIT
3
RL _ MAX ) GCS _ MIN
/ I OCSET
(11)
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 RDRP resistor, see figure 6. The Error Amplifier forces the voltage on the FB pin to equal VREF through the
power supply loop therefore the current through RDRP is equal to (VDRP-VREF) / RDRP. As the load current
increases, the VDRP voltage increases accordingly which results in an increase in RFB current, positioning the
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 RDRP. The
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 RO*IO, where RO is the required output impedance of the converter. RDRP
is determined by Equation (12)
RDRP
RFB RL _ MAX GCS _ MIN
n RO
(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,
1
vC (s) vL (s) 1 sRS CS
iL
(
s)
1
RL sL
sRS CS
(13)
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 RL was used. The mismatch of the time constants does not affect the measurement of
inductor DC current, but affects the AC component of the inductor current.
Page 18 of 29
09/26/05
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