© 2020 Crocus Technology 1
Document #: AN124 – Low Current Sensing Applications Rev0.0
Low Current Sensing Applications
Introduction
Crocus Technology is extending its current sensing
product portfolio to include a high bandwidth, low
current sensor up to ±15 A
PK
. Based on its patented
TMR technology, the CT110 features superior
linearity and over temperature performance with the
capability of sensing current as low as 10 mA to
enable a high dynamic range.
The CT110 is a 6-pin device that features a linear
ratiometric analog output in addition to a digital active
low over-current protection output that is triggered in
under 0.5 µs.
It is a factory trimmed device that guarantees the
sensor gain and the over-current protection threshold.
Operating Principle
The CT110 is an isolated device that measures the
magnetic field generated by the current flowing inside
the package.
Figure 1: CT110 packaging showing the die, pads
and current carrying conductor.
The galvanic separation between the die and the
current carrying conductor allows the sensor to
perform isolated current measurements.
Figure 2: Cross-section of the CT110 package
showing the internal magnetic field.
The CT110 sensor is based on a monolithic die that
includes a highly linear 1D TMR sensor configured in
a full-bridge layout, and an integrated circuit for
amplification, gain, and over-current protection
threshold trimming.
Figure 3: CT110 block diagram.
The CT110 is factory trimmed and cannot be re-
programmed on the application side.
© 2020 Crocus Technology 2
Document #: AN124 – Low Current Sensing Applications Rev0.0
Reference Design
The CT110 measures bi-directional current, hence
the ANA output pin is trimmed to be equal to half of
V
DD
when the current is null and varies towards VDD
or GND depending on the direction of the current. The
sensor does not require any additional circuitry and
can be connected directly to an ADC or comparator.
VDD
3
2
1
Isolation
Barrier
Expo sed Pad
Analog
Front-End
State Machine
Analog
MLU
Digital
(Push-pull)
FLAG
4
1.0 µF
2.7 V to 5.5 V
Measured
Current
GND
ANA
1 2
Resistor
R1
10 pF
47 kΩ
Figure 4: CT110 application block diagram.
Below is a recommended circuit featuring the CT110
along with a decoupling capacitor C1 = 1.0 µF. An RC
filter may be connected to the ANA pin to lower noise.
Figure 5: CT110 application schematic diagram.
The graphic in Figure 6 shows the top layer for the
printed circuit board (PCB) layout for the EVB111, the
evaluation board for CT110.
Figure 6: Typical GDS layout of the top layer for
the CT110 evaluation board, EVB111.
In Figure 7, this is the PCB layout for the bottom or
ground layer of EVB111.
Figure 7: Typical GDS layout of the ground layer
for the CT110 evaluation board.