IR3553_15 datasheet(15/22 Pages) IRF

15 / 22 page

July 16, 2014 | DATASHEET V3.3

IR3553

40A Integrated PowIRstage®

VIN

CSIN+

CSIN-

IR3553

VIN

VOUT

CIN

CCS

COUT

RCS

+ vCS -

Current

Sense

Amplifier

Figure 31: Inductor current sensing

Usually the resistor RCS and capacitor CCS are chosen so that

the time constant of RCS and CCS equals the inductor time

constant, which is the inductance L over the inductor DCR

(RL). 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.

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 IR3553, as shown in Figure 6. Its gain is nominally

32.5, and the inductor DCR increase with temperature is

not compensated inside the IR3553. 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.

If the IR3553 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.

MAXIMUM OUTPUT VOLTAGE

When the IR3553 current sense amplifier is used, the

maximum output voltage is limited by the VCC voltage

used and should be lower than VCC – 2.5V to ensure

enough headroom for the current sense amplifier. The

maximum voltage is 4.3V when 6.8V VCC is used, but is

only 2.5V when 5V VCC is used. The maximum voltage is

4.3V when 6.8V is used for the VCC.

When the IR3553 current sense amplifier is not used, the

maximum voltage is not limited by the VCC voltage. The

IR3553 can support output voltage up to 5.5V but the

output current must be derated since the MOSFET ratio

was optimized for duty cycles of 10% to 20%.

DESIGN PROCEDURES

POWER LOSS CALCULATION

The single-phase IR3553 efficiency and power loss

measurement circuit is shown in Figure 32.

The IR3553 power loss is determined by,

OUT

VCC

LOSS













Where both MOSFET loss and the driver loss are included,

but the PWM controller and the inductor losses are not.

IR3553 数据表(PDF) 15 Page - International Rectifier

IR3553 数据表(HTML) 15 Page - International Rectifier

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

数据表下载