IR3502BMPBF International Rectifier, IR3502BMPBF Datasheet - Page 12

• Manufacturer Part Number: IR3502BMPBF
• Description: The IR3502B control IC combined with an XPHASE3 Phase IC provides a full featured and flexible way to implement a complete VR11.0 and VR11.1 power solution.
• Manufacturer: International Rectifier

Specifications of IR3502BMPBF

• Package: 32-Lead MLPQ
• Circuit: X-Phase Control IC
• Switch Freq (khz): 250kHz to 1.5MHz
• Pbf: PbF Option Available

resistor with the value of R
inductor DC current, but affects the AC component of the inductor current.
The advantage of sensing the inductor current versus high side or low side sensing is that actual output current being
delivered to the load is obtained rather than peak or sampled information about the switch currents. The output voltage
can be positioned to meet a load line based on real time information. Except for a sense resistor in series with the
inductor, this is the only sense method that can support a single cycle transient response. Other methods provide no
information during either load increase (low side sensing) or load decrease (high side sensing).
An additional problem associated with peak or valley current mode control for voltage positioning is that they suffer
from peak-to-average errors. These errors will show in many ways but one example is the effect of frequency variation.
If the frequency of a particular unit is 10% low, the peak to peak inductor current will be 10% larger and the output
impedance of the converter will drop by about 10%. Variations in inductance, current sense amplifier bandwidth, PWM
prop delay, any added slope compensation, input voltage, and output voltage are all additional sources of peak-to-
average errors.
Current Sense Amplifier
A high speed differential current sense amplifier is located in the phase IC, as shown in Figure 6. Its gain is nominally
33 at 25ºC, and the 3850 ppm/ºC increase in inductor DCR should be compensated in the voltage loop feedback path.
The current sense amplifier can accept positive differential input up to 50mV and negative up to -10mV before clipping.
The output of the current sense amplifier is summed with the VDAC voltage and sent to the control IC and other
phases through an on-chip 3KΩ resistor connected to the IIN pin. The IIN pins of all the phases are tied together and
the voltage on the share bus represents the average current through all the inductors and is used by the control IC for
voltage positioning and current limit protection. The input offset of this amplifier is calibrated to +/- 1mV in order to
reduce the current sense error.
The input offset voltage is the primary source of error for the current share loop. In order to achieve very small input
offset error and superior current sharing performance, the current sense amplifier continuously calibrates itself. This
calibration algorithm creates ripple on IIN bus with a frequency of fsw/(32*28) in a multiphase architecture.
Average Current Share Loop
Current sharing between the phases of the converter is achieved by the average current share loop in each phase IC.
The output of the current sense amplifier is compared with average current at the share bus. If current in a phase is
smaller than the average current, the share adjust amplifier of the phase will pull down the starting point of the PWM
ramp thereby increasing its duty cycle and output current; if current in a phase is larger than the average current, the
share adjust amplifier of the phase will pull up the starting point of the PWM ramp thereby decreasing its duty cycle and
output current. The current share amplifier is internally compensated; such that, the crossover frequency of the current
share loop is much slower than that of the voltage loop and the two loops do not interact.
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Figure 6 Inductor Current Sensing and Current Sense Amplifier
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was used. The mismatch of the time constants does not affect the measurement of
CSOUT
Current
Sense Amp
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IR3502B
V3.2