Si85xx
2. Functional Overview
The Si85xx AC Current Sensor family of products mimic
the functionality of a traditional current transformer (CT)
circuit with burden resistor, diode and output filter, but
offers enhanced performance and added capabilities.
These devices use inductive current sensing and on-
board signal conditioning electronics to generate a 2 V
full-scale output signal proportional to the ac current
flowing from the IIN to the IOUT terminals. As shown in
package slug induces a signal in the pickup coil on-
board the Si85xx die. This signal is applied to the input
of an integrator that re-constructs the ac current flowing
from IIN to IOUT. On-board circuitry provides cycle-by-
cycle integrator reset, and temperature and offset
voltage compensation to achieve measurement
accuracy to within ±5%.
IIN
R1
R2
R3
R4
Si851x
RESET LOGIC
MODE LOGIC
MODE
OUT1
METAL SLUG
INTEGRATOR
SIGNAL CONDITIONING
OUT2
PICKUP
COIL
TEMP
SENSOR
ADC
AUTO CALIBRATION
LOGIC
IOUT
GND
VDD
TRST/FAULT
IIN
R1
R2
Figure 2. Si851x (Ping Pong Output) Block
Diagram
Si850x
RESET LOGIC
VDD2
The Si85xx is superior to other current sensing
approaches and benefits the system in a number of
ways:
Small size:
With its 4x4 mm footprint and 1 mm
height, the Si85xx is among the smallest current
sensors available.
Large output signal:
The 2.0 V full-scale output
swing offers superior noise immunity versus other
current sensing technologies.
Low loss:
The Si85xx adds only 1.3 mΩ (at 25 °C)
to the sensing path making it one of the lowest loss
current sensors available. Low 2 nH primary series
inductance is 2,000 times lower compared to a CT,
and results in significantly less ringing.
High precision:
The Si8501/2/3 versions are
available with a max error of ±5% of reading; one of
the highest accuracy current sensors available.
Ping-Pong output mode (Si851x):
Alternately
routes the current measurements from each side of
a full-bridge circuit to separate output pins for
comparison, which is very useful for transformer flux
balancing applications. Eliminates a second CT in a
full-bridge application.
Leading edge noise suppression:
Filters out
reflected noise due to long reverse recovery time of
output rectifier. Eliminates the need for external
leading edge blanking circuit.
High common mode voltage:
The Si85xx offers up
to 1,000 VDC of isolation making it useful over a
very wide voltage range.
METAL SLUG
INTEGRATOR
SIGNAL CONDITIONING
OUT
PICKUP
COIL
TEMP
SENSOR
ADC
AUTO CALIBRATION
LOGIC
NC
IOUT
GND2
GND1
VDD1
GND3
TRST
Figure 1. Si850x (Single Output) Block Diagram
6
Preliminary Rev. 0.1
SILABS [ SILICON LABORATORIES ]
