HCPL-7840-560E Avago Technologies US Inc., HCPL-7840-560E Datasheet - Page 18

• Manufacturer Part Number: HCPL-7840-560E
• Description: Optocoupler
• Manufacturer: Avago Technologies US Inc.

Specifications of HCPL-7840-560E

• No. Of Channels: 1
• Isolation Voltage: 3.75kV
• Optocoupler Output Type: Analog
• Input Current: 15.5mA
• Output Voltage: 3.8V
• Opto Case Style: SMD
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): Yes
• Reel Quantity: 1000
• Amplifier Type: Isolation
• Number Of Circuits: 1
• Output Type: Differential
• -3db Bandwidth: 100kHz
• Current - Input Bias: 500nA
• Voltage - Input Offset: 300µV
• Current - Supply: 10.9mA
• Current - Output / Channel: 15.5mA
• Voltage - Supply, Single/dual (±): 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SMD Gull Wing
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Slew Rate: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

FREQUENTLY ASKED QUESTIONS ABOUT THE HCPL-7840
1. THE BASICS
1.1: Why should I use the HCPL-7840 for sensing current when Hall-effect sensors are available which don’t need an
isolated supply voltage?
Available in an auto-insertable, 8-pin DIP package, the HCPL-7840 is smaller than and has better linearity, offset vs.
temperature and Common Mode Rejection (CMR) performance than most Hall-effect sensors. Additionally, often the
required input-side power supply can be derived from the same supply that powers the gate-drive optocoupler.
2. SENSE RESISTOR AND INPUT FILTER
2.1: Where do I get 10 mΩ resistors? I have never seen one that low.
A l t h o u g h l e s s c o m m o n t h a n v a l u e s a b o v e 1 0 Ω , t h e r e a r e q u i t e a fe w m a n u f a c t u r-
ers of resistors suitable for measuring currents up to 50 A when combined with the HCPL- 7840.
Example product information may be found at Dale’s web site (http://www.vishay.com/vishay/dale) and Isotek’s web
site (http://www.isotekcorp.com).
2.2:
This is not necessary, but it will work. If you do, be sure to use an RC filter on both pin 2 (V
the input voltage at both pads.
2.3: Do I really need an RC filter on the input? What is it for? Are other values of R and C okay?
The input anti-aliasing filter (R=39 Ω, C=0.01 µF) shown in the typical application circuit is recommended for filtering
fast switching voltage transients from the input signal. (This helps to attenuate higher signal frequencies which could
otherwise alias with the input sampling rate and cause higher input offset voltage.)
Some issues to keep in mind using different filter resistors or capacitors are:
1. (Filter resistor:) Input bias current for pins 2 and 3: This is on the order of 500 nA. If you are using a single filter resis-
tor in series with pin 2 but not pin 3 the IxR drop across this resistor will add to the offset error of the device. As long
as this IR drop is small compared to the input offset voltage there should not be a problem. If larger-valued resistors
are used in series, it is better to put half of the resistance in series with pin 2 and half the resistance in series with pin
3. In this case, the offset voltage is due mainly to resistor mismatch (typically less than 1% of the resistance design
value) multiplied by the input bias.
2. (Filter resistor:) The equivalent input resistance for -7840 is around 500 kΩ. It is therefore best to
ensure that the filter resistance is not a significant percentage of this value; otherwise the offset voltage
will be increased through the resistor divider effect. [As an example, if R
2 mV for a maximum 200 mV input and V
3. The input bandwidth is changed as a result of this different R-C filter configuration. In fact this is one of the main
reasons for changing the input-filter R-C time constant.
4. (Filter capacitance:) The input capacitance of the -78XX is approximately 1.5 pF. For proper operation the switching
input-side sampling capacitors must be charged from a relatively fixed (low impedance) voltage source. Therefore, if
a filter capacitor is used it is best for this capacitor to be a few orders of magnitude greater than the C
at least 100 pF works well.)
2.4: How do I ensure that the HCPL-7840 is not destroyed as a result of short circuit conditions which cause voltage
drops across the sense resistor that exceed the ratings of the HCPL-7840’s inputs?
Select the sense resistor so that it will have less than 5 V drop when short circuits occur. The only other requirement
is to shut down the drive before the sense resistor is damaged or its solder joints melt. This ensures that the input of
the HCPL-7840 can not be damaged by sense resistors going open-circuit.
18
to pin 4?
Should I connect both inputs across the sense resistor instead of grounding V
OS
will vary with respect with Vin.]
filt
= 5.5 kΩ, then V
IN+
) and pin 3 (V
OS
= (Vin * 1%) =
INPUT
IN-
IN-
(A value of
) to limit
directly