ACPL-C797-500E Avago Technologies US Inc., ACPL-C797-500E Datasheet - Page 13

• Manufacturer Part Number: ACPL-C797-500E
• Description: Isolated Sigma-Delta, T/R+IEC+LF
• Manufacturer: Avago Technologies US Inc.
• Series: -r
• Type: Sigma-Delta Modulatorr

Specifications of ACPL-C797-500E

• Voltage - Isolation: 5000Vrms
• Input Type: DC
• Voltage - Supply: 3 V ~ 5.5 V, 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.268", 6.81mm Width)
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Available in an SO-16 surface-mount package, the Digital
Interface IC has features include five different conversion
modes (combinations of speed and resolution), three
different pre-trigger modes (allows conversion time <
1 Ps), offset calibration, fast over-range (over-current,
or short circuits) detection, and adjustable threshold
detection. Programmable features are configured via the
Serial Configuration port. A second multiplexed input is
available to allow measurements with a second isolated
modulator without additional hardware. Refer to the
HCPL-0872 data sheet for details.
Notes:
SPI and QSPI are trademarks of Motorola Corp.
Microwire is a trademark of National Semiconductor Inc.
Figure 19. Typical application circuit for motor phase current sensing
Power Supplies and Bypassing
As shown in Figure 19, a floating power supply (which in
many applications could be the same supply that is used
to drive the high-side power transistor) is regulated to 5
V using a simple zener diode (D1); the value of resistor
R1 should be chosen to ensure sufficient current can be
supplied from the existing floating supply. The voltage
from the current sensing resistor or shunt (R
applied to the input of the ACPL-C797 through an RC anti-
aliasing filter (R2 and C2). And finally, a clock is connected
to the ACPL-C797 and data are connected to the digital
filter. Although the application circuit is relatively simple,
a few recommendations should be followed to ensure
optimal performance.
The power supply for the isolated modulator is most
often obtained from the same supply used to power the
power transistor gate drive circuit. If a dedicated supply
is required, in many cases it is possible to add an addi-
tional winding on an existing transformer. Otherwise,
some sort of simple isolated supply can be used, such as
13
MOTOR
+
R
SENSE
–
HV+
HV–
CIRCUIT
DRIVE
GATE
R2 4.3 :
FLOATING
POSITIVE SUPPLY
5.1 V
D1
100 nF
C2
GND1
C1a 1 PF
R1
C1b 0.1 PF
SENSE
) is
V
V
V
GND1
DD1
IN +
IN –
ISOLATION
ACPL-C797
Application Information
Digital Current Sensing Circuit
Figure 19 shows a typical application circuit for motor
control phase current sensing. By choosing the appro-
priate shunt resistance, a wide range of current can be
monitored, from less than 1 A to more than 100 A.
a line powered transformer or a high-frequency DC-DC
converter.
An inexpensive 78L05 three terminal regulator can also be
used to reduce the floating supply voltage to 5 V. To help
attenuate high-frequency power supply noise or ripple, a
resistor or inductor can be used in series with the input of
the regulator to form a low-pass filter with the regulator’s
input bypass capacitor.
As shown in Figure 19, bypass capacitors (C1a, C1b, C3a
and C3b) should be located as close as possible to the
input and output power-supply pins of the isolated
modulator. The bypass capacitors are required because
of the high-speed digital nature of the signals inside the
isolated modulator. A bypass capacitor (C2) is also recom-
mended at the input due to the switched-capacitor nature
of the input circuit. The input bypass capacitor also forms
part of the anti-aliasing filter, which is recommended to
prevent high frequency noise from aliasing down to lower
frequencies and interfering with the input signal.
BARRIER
MDAT
MCLK
GND2
V
DD2
ISOLATED
5 V/3.3 V
GND2
NON-
C3a
0.1 PF
C3b
1 PF