IR21771STRPBF International Rectifier, IR21771STRPBF Datasheet - Page 11

• Manufacturer Part Number: IR21771STRPBF
• Description: IC CURRENT SENSE 16SOIC
• Manufacturer: International Rectifier

Specifications of IR21771STRPBF

• Function: Current Sense
• Voltage - Input: 8 ~ 20 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Accuracy: -
• Sensing Method: -

1.4 DC transfer functions
The working principle of the device can be easily
explained by Figure 10, in which the main signals
are represented.
PWM out (PO pin) gives a duty cycle which is
inversely proportional to the input signal.
Eq. 2 gives the resulting D
pin):
Eq. 2
where V
11
Triangular
reference
SYNC
Figure 10: Main current sensor signals and
Vin
PO
D
n
in
Figure 11: PO Duty Cycle (D
=
= V
PO duty cycle
20
inp
%
-V
−
inm
40
outputs
%
V
30%
25%
20%
15%
10%
⋅
V
n
in
of the PWM output (PO
n
)
V
in
1.5 Filter AC characteristic
IR21771/22771 signal path can be considered as
composed by three stages in series (see Figure 13).
The first two stages perform the filtering action.
Stage 1 (input filter) implements the filtering action
originating the transfer function shown in Figure 14.
The input filter is a self-adaptive reset integrator
which performs an accurate ripple cancellation. This
stage extracts automatically the PWM frequency
from Sync signal and puts transmission zeros at
even harmonics, rejecting the unwanted PWM
noise.
The following timing diagram shows the principle by
which even harmonics are rejected (Figure 12).
As can be seen from Figure 14, the odd harmonics
are rejected as a first order low pass filter with a
single pole placed in f
The input filter group delay in the pass-band is very
low (see GD on AC electrical characteristics) due to
the beneficial action of the zeroes.
Figure 12: Even harmonic cancellation principle
IR22771S/IR21771S(PbF)
PWM
www.irf.com
.