IR3513ZMTRPBF International Rectifier, IR3513ZMTRPBF Datasheet - Page 15

• Manufacturer Part Number: IR3513ZMTRPBF
• Description: IC CTRL XPHASE3 POL 32-MLPQ
• Manufacturer: International Rectifier
• Series: XPhase3™r

Specifications of IR3513ZMTRPBF

• Applications: Processor
• Current - Supply: 3mA
• Voltage - Supply: 8 V ~ 16 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: *
• Package: 32-Lead MLPQ
• Circuit: X-Phase Control IC
• Switch Freq (khz): 250kHz to 1.5MHz
• Pbf: PbF Option Available
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 included in both the IR3513 and optional phase ICs, 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 VREF voltage and sent to other phases
through an on-chip 3KΩ resistor connected to the ISHARE pin. The ISHARE 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 ISHARE bus with a frequency of fsw/896.
Average Current Share Loop
Current sharing between 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 so 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.
Page 15
Figure 6 - Inductor Current Sensing and Current Sense Amplifier
REPLACEMENT PRODUCT – IR3513ZMTRPBF
NOT RECOMMENDED FOR NEW DESIGNS
CSOUT
Current
Sense Amp
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CS
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May 11, 2008
IR3513