IR2177 International Rectifier Corp., IR2177 Datasheet - Page 14

• Manufacturer Part Number: IR2177
• Description: Phase Current Sensor Ic For Ac Motor Control
• Manufacturer: International Rectifier Corp.

1.5 DC transfer functions
The working principle of the device can be easily
explained by Figure 13, in which the main signals
are represented.
PWM out (PO pin) gives a duty cycle which is
inversely proportional to the input signal while the
OUT pin gives the analog converted output.
Eq. 2 gives the resulting D
pin):
Eq. 2
where V
The Voltage-to-Time conversion (V
reconstructed (see Functional Block Diagram) to
give an analog voltage output at OUT pin.
OUT pin swings from V
output (referred to V
14
Triangular
reference
SYNC
Figure 13: Main current sensor signals and
VRH
OUT
VRL
Vin
PO
D
n
in
Figure 14: PO Duty Cycle (D
=
= V
20
PO duty cycle
inp
%
-V
−
inm
40
SS
outputs
) follows Eq. 3:
%
V
⋅
RL
V
30%
25%
20%
15%
10%
n
in
of the PWM output (PO
to V
RH
in
, so the analog
to PO) must be
n
)
V
in
Eq. 3
The same equation can be referred to V
follows in Eq. 4:
Eq. 4
OUT
Figure 15: ideal OUT/V
OUT
−
V
RL
=
=
2
2
⋅
⋅
(
(
V
V
IR2277S/IR2177S(PbF)
RH
OUT
RH
−
−
V
V
RL
RL
V
V
(V
in
RL
RH
)
)
RH
transfer function
⋅
⋅
V
V
+V
in
in
RL
+
+
)/2
V
V
RH
RH
www.irf.com
RL
2
+
2
−
, as
V
V
V
in
RL
RL