IR3551MTRPBF International Rectifier, IR3551MTRPBF Datasheet - Page 15

• Manufacturer Part Number: IR3551MTRPBF
• Description: The IR3551 integrated PowIRstage is a synchronous buck gate driver IC with co-packed control and synchronous MOSFETs and Schottky diode.
• Manufacturer: International Rectifier

Specifications of IR3551MTRPBF

• Package: PQFN / 5 x 6
• Iout (a): 50
• Switch Freq (khz): up to 1.0MHz
• Input Range (v): 4.5 - 15
• Output Range (v): 0.25 - (VCC -2.5)

constant, which is the inductance L over the inductor DCR
(R
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
does not affect the measurement of 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. 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).
CURRENT SENSE AMPLIFIER
A high speed differential current sense amplifier is located
in the IR3551, as shown in Figure 6. Its gain is nominally
32.5, and the inductor DCR increase with temperature is
not compensated inside the IR3551. The current sense
amplifier output IOUT is referenced to REFIN, which is
usually connected to a reference voltage from the PWM
controller. Figure 27 shows the differential voltage of
V(IOUT) – V(REFIN) versus the inductor current and reflects
the inductor DCR increase with temperature at higher
current.
The current sense amplifier can accept positive differential
input up to 25mV and negative input up to -10mV before
clipping. The output of the current sense amplifier is
summed with the reference voltage REFIN and sent to the
IOUT pin. The REFIN voltage is to ensure at light loads
there is enough output range to accommodate the
negative current ripple shown in Figure 28. In a multiphase
converter, the IOUT pins of all the phases can be tied
together through resistors, and the IOUT voltage
represents the average current through all the inductors
and is used by the controller for adaptive voltage
positioning.
The input offset voltage is the primary source of error for
the current signal. In order to obtain very accurate current
signal, the current sense amplifier continuously calibrates
itself, and the input offset of this amplifier is within +/-
450uV. This calibration algorithm can create a small ripple
on IOUT with a frequency of fsw/128.
L
). If the two time constants match, the voltage across C
L
was used. The mismatch of the time constants
15
March 12, 2012 | FINAL DATASHEET
50A Integrated PowIRstage®
CS
If the IR3551 current sense amplifier is required, connect
its output IOUT and the reference voltage REFIN to the
PWM controller and connect the inductor sense circuit as
shown in Figure 4. If the current sense amplifier is not
needed, tie CSIN+, CSIN- and REFIN pins to LGND and float
IOUT pin, as shown in Figure 5.
DESIGN PROCEDURES
POWER LOSS CALCULATION
The single-phase IR3551 efficiency and power loss
measurement circuit is shown in Figure 32.
The IR3551 power loss is determined by,
Where both MOSFET loss and the driver loss are included,
but the PWM controller and the inductor losses are not
included.
Figure 7 shows the measured single-phase IR3551
efficiency under the default test conditions, V
V
T
The efficiency of an interleaved multiphase IR3551
converter is always higher than that of a single-phase
under the same conditions due to the reduced input RMS
current and more input/output capacitors.
The measured single-phase IR3551 power loss under the
same conditions is provided in Figure 8.
VCC
AMBIENT
OUT
10k
R1
=1.2V, ƒ
I
VCC
1nF
C7
= 25°C, no heat sink, and no air flow.
Figure 32: IR3551 Power Loss Measurement
1uF
C3
P
LOSS
SW
VCC
PHSFLT#
PWM
BBRK#
LGND
REFIN
IOUT
= 400kHz, L=150nH (0.29mΩ), VCC=7V,

V
IR3551
IN

I
IN
BOOST
PGND
CSIN+
CSIN-

VIN
SW
V
CC

I
VCC
0.22uF
0.1uF x2
C5
C1

V
2.49k
SW
R2
150nH
V
IR3551
L1
SW

0.22uF
I
C4
47uF x4
I
OUT
IN
C2
V
IN
I
IN
OUT
470uF x3
=12V,
C6
V
OUT