IR3505MPBF International Rectifier, IR3505MPBF Datasheet - Page 13

• Manufacturer Part Number: IR3505MPBF
• Description: IC XPHASE3 CONTROL 16-MLPQ
• Manufacturer: International Rectifier
• Series: XPhase3™r

Specifications of IR3505MPBF

• Applications: Processor
• Current - Supply: 3mA
• Voltage - Supply: 8 V ~ 16 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Emulated Bootstrap Diode
IR3505 integrates a PFET to emulate the bootstrap diode. An external bootstrap diode connected from VCCL
pin to BOOST pin can be added to reduce the drop across the PFET but is not needed in most applications.
APPLICATIONS INFORMATION
IR3505 EXTERNAL COMPONENTS
Inductor Current Sensing Capacitor C
The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor R
C
across the capacitor C
component of the capacitor voltage is different from that of the real inductor current. The time constant mismatch
does not affect the average current sharing among the multiple phases, but does effect the current signal ISHARE
as well as the output voltage during the load current transient if adaptive voltage positioning is adopted.
Measure the inductance L and the inductor DC resistance R
follows.
Bootstrap Capacitor C
Depending on the duty cycle and gate drive current of the phase IC, a capacitor in the range of 0.1uF to 1uF is
needed for the bootstrap circuit.
Decoupling Capacitors for Phase IC
A 0.1uF-1uF decoupling capacitor is required at the VCCL pin.
CURRENT SHARE LOOP COMPENSATION
The internal compensation of current share loop ensures that crossover frequency of the current share loop is at
least one decade lower than that of the voltage loop so that the interaction between the two loops is eliminated.
The crossover frequency of current share loop
Output Voltage Bleed Resistor
The floating high side driver draws bias current from the BOOST pin (3.5mA typical). This current flows out of
the IR3505 through the SW pin and will charge up the output capacitor when the control IC is disabled. A
bleed resistor connected from the converter output voltage to ground is required to prevent the output voltage
from exceeding the control IC Over-Voltage protection threshold. The bleed resistor can be selected using the
following equation.
Where V
converter.
Optional phases
A converter can be designed to support more or less phases. This can be quite useful in situations where the final
load current is unknown or where increased load current may be required at some time in the future.
CS
in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage
Page 13 of 19
BLEED
is the maximum desired output voltage pre-bias and N is the number of IR3505 used in the
CS
BST
R
CS
represents the inductor current. If the two time constants are not the same, the AC
=
L
C
R
CS
R
L
BLEED
= V
CS
and Resistor R
BLEED
is approximately 8 kHz.
/ (5.8mA x N)
CS
L
. Pre-select the capacitor C
(2)
CS
(1)
Sept 26
and calculate R
CS
th
IR3505
, 2007
and capacitor
CS
as