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Current Sense Amplifier – SiSA4080

Rev 1.0

14/10/20

Application Notes

Formulae

Sense Resistor Selection

Select RSENSE based on the following criteria:

Output Voltage:

VOUT = VSENSE 5 AV



Voltage Loss - A high RSENSE value causes the

power-source voltage to degrade through IR loss.

For minimal voltage loss, use the lowest RSENSE

value.

Where:



VSENSE is the full-scale sense voltage



Accuracy - A high RSENSE value allows lower

currents to be measured more accurately. This is

due to offsets becoming less significant when the

sense voltage is larger. For best performance,

select RSENSE to provide approximately 100mV of

sense voltage for the full-scale current in each

application.



AV is the gain of the device.

The Full-Scale Output Voltage is:

VOUT = RSENSE × ILOAD (MAX) × AV

VSENSE(MAX) = 100mV for 60V/V gain



Efficiency and Power Dissipation - At high current

levels, the I2R losses in RSENSE can be significant.

Take this into consideration when choosing the

resistor value and its power dissipation (wattage)

rating. Also, the sense resistor’s value might drift if

it is allowed to heat up excessively.

Power-Supply Bypassing and Grounding

For most applications, bypass VCC to GND with a 0.1µF

ceramic capacitor. In many applications, VCC can be

connected to one of the current monitor terminals (RS+

or RS-). Because VCC is independent of the monitored

voltage, VCC can be connected to a separate regulated

supply. If VCC will be subject to fast-line transients, a

series resistor can be added to the power-supply line to

minimize output disturbance. This resistance and the

decoupling capacitor reduce the rise time of the

transient. For most applications, 1kΩ in conjunction with

a 0.1µF bypass capacitor works well. In bare die form

the backside of the die should be isolated, in package

form the device requires no special considerations with

respect to layout or grounding. Consideration should be

given to minimizing errors due to the large charge and

discharge currents in the system.



Inductance - Keep inductance low if ISENSE has a

large high-frequency component. Wire-wound

resistors have the highest inductance, while metal

film is somewhat better. Low-inductance, metal-

film resistors are also available. Instead of being

spiral- wrapped around a core, as in metal-film or

wire-wound resistors, they are a straight band of

metal and are available in values under 1Ω.

Because of the high currents that flow through

RSENSE, take care to eliminate parasitic trace

resistance from causing errors in the sense

voltage. Either use a four-terminal current-sense

resistor or use Kelvin (force and sense) PC board

layout techniques.

DISCLAIMER: The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. With respect to

any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Silicon Supplies Ltd

hereby disclaims any and all warranties and liabilities of any kind.

LIFE SUPPORT POLICY: Silicon Supplies Ltd components may be used in life support devices or systems only with the express written

approval of Silicon Supplies Ltd, if a failure of such components can reasonably be expected to cause the failure of that life support device or system or

to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to

support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may

be endangered.

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