Intersil ISL28133ISENSEV1Z User Manual

Page 1

Application Note 1480

ISL28133ISENSEV1Z Evaluation Board User’s Guide

The ISL28133ISENSEV1Z evaluation board contains a complete precision current sense amplifier using the ISL28133 chopper amplifier in a high side, low side of floating supply current sense application.

The advantages of the ISL28133 in this application include very low offset voltage (2µV typical) and offset drift (0.07µV/°C), rail-to-rail input and output and low power consumption (18µA typical). These features provide a very high degree of precision for use in 5V, low power applications.

Reference Documents

• ISL28133 Data Sheet (FN6560)

Evaluation Board Key Features

The ISL28133ISENSEV1Z operates from a single 1.65VDC to +5.5VDC supply. The current sense function is configured as a single stage, balanced input, trans-impedance amplifier. A

0.1Ω 0.1% current sense resistor is used convert the incoming current to a voltage which is applied to a precision differential amplifier with a gain of 100. The overall current to voltage transfer ratio is 10V/A, and a bidirectional current range of ±0.25A is achieved when operating from a +5V supply, using a

2.5V reference voltage (V achieves a total full scale offset error of 0.038% (when a precision external reference is used) and approximately 0.15% using the internal 0.1% resistors.

The total current draw from the amplifier power is less than 35µA and the total leakage current from the current sense input is less than 3µA.

). At +25°C, the ISL28133

REF

High speed current sensing may involve filtering repetitive current transients with high peak to average values. In these cases, limiting these transient even further will improve amplifier response and overload settling time. The optional Schottky diode transient clamp D2 reduces transients let through by the common mode clamp from 6V down to ~ ±0.3V, which improves overload recovery time. Capacitors C7 and C9 provide common mode noise filtering and capacitor C8 can be used to filter the current sense signal.

Current Sense Gain Equations

The current sense amplifier in Figure 1 forms a trans-impedance amplifier whose gain is in units of V/A and is determined by the ratios of resistor pairs. R11:R8 and R14: R9. Resistor R11 is set equal to R14 and R8 is set equal to R9. This matching cancels the input offset voltage errors caused by the op amp input bias currents, leaving behind only the offset voltage errors caused by the ISL28133 input offset

SENSE

to V

DC transfer function is given by Equation 1:

OUT

---

R14

---------- -

× V

SENSE

REF

is 0.1Ω for a trans-impedance

(EQ. 1)

(EQ. 2)

current (I

The I

OUTISENSERSENSE

where:

R11 = R14 and R6 + R8 = R7 + R9

On the evaluation board, the R12, R9 resistor ratio is 100:1 (499kΩ: 4.9kΩ), and R gain given by Equation 2:

SENSE

------------------- -

SENSE

Power Supply and Protection Features

External power connections are made through the +V, and ground jacks. The single supply input is overvoltage protected using a series 100Ω resistor and a 5.6V zener diode (D1). Reverse polarity protection uses the 100Ω resistor and two protection diode pairs (D3, D4). These also provide input common mode voltage protection to the op amp.

Input Protection Clamp Options

Included on the evaluation board are optional input protection circuits that illustrate the best methods to limit input common mode and differential transient voltage spikes in exposed or electrically hazardous applications. The ISL28133 can handle input common mode and differential transients to a diode drop beyond the rails, or to a range of -0.5V to +5.5V when operating from a single 5V supply.

Clamp diodes D3A, B, D4A, B and input resistors R6, R7, R8, R9 form a current limiting, 6V common mode and differential voltage clamp. This clamp provides sufficient protection for the ISL28133 for common mode fault voltages far beyond the power supply rails. These diodes also provide the same 6V protection against large differential transients.

Input Range and Offset Error Analysis

The ISL28133 output swings from rail-to-rail, and the evaluation board has a bi-directional output range of V operated from a +5V supply and V

is set to VS/2. The

REF

evaluation board contains a jumper-selectable, internal V reference or an external reference (V

REF

+2.5, the full scale output range is 0 ±0.25A.

The very low offset voltage (±8µV +25°C max) and offset current (300pA +25°C max) of the ISL28133 enable the use of very high values resistors for low current consumption while maintaining excellent precision in battery operated circuits. The total offset voltage contribution of the ISL28133 is the sum of the input offset voltage (V

) and the offset voltage

produced by the input offset current (IOS) through the gain resistors and using the evaluation board resistor values and the data sheet maximum +25°C V

gives the total input

offset voltage as shown in Equations 3, 4 and 5:

R14 R9×

⎛⎞

-------------------------

OS Total()

IOS

⎝⎠

R14 R9+

VOS+=

±2.5V when

REF

pin). With V

REF

set to

(EQ. 3)

July 18, 2011 AN1480.2

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.

All other trademarks mentioned are the property of their respective owners.

Page 2

Application Note 1480

OS Total()

⎛⎞

3e 10

⎝⎠

3e 10 4950×–()= 8μ V9.5μV=+

R14 R9×

-------------------------

×–

R14 R9+

8μ V+=

(EQ. 4)

(EQ. 5)

Multiplying the ISL28133 input offset voltage by the amplifier gain allows the input offset error to be expressed as a percent of full scale output voltage.

R14

---------- -

(EQ. 6)

2.5V±

% F.S. Error

⎛⎞ ⎝⎠

------------------------------------ -

= 0.038%±=

Using the Evaluation Board

The evaluation board has separate connections for the amplifier power supply, an output zero reference (V sense terminals. The correct inter-connection between the ISENSE terminals and the V

terminals are needed to

REF

implement the different types of current sense configurations.

The I-SENSE + and I-SENSE - connections to the measured circuit determine the polarity of the amplifier output voltage. Establishing a current flow from the I-SENSE + to I-SENSE causes the output voltage to increase in proportion to the input current. Reversing the I-SENSE current flow reverses the output polarity.

I-SENSE+

10Ω

DNPR2DNPR30.1R4DNPR5DNP

10Ω

1nF

),and the current

REF

D3A

4.99k

C8 10nF

4.99k

C9 1nF

D3B D4B

D4A

The voltage applied to the V

pin defines the amplifier output

REF

zero current level, and must be between 0V and +5V. For bi-directional current sensing, a reference midway between the ground and the supply voltage will maximize the output span. For example, a V

= +2.5V would be the best choice for +5V power

REF

supply. The jumper selectable internal voltage divider is provided for this internal reference. The +2.5V will establish an output current scale setting 0A = +2.5V, but the accuracy is determined by the voltage divider accuracy (0.1% resistors on the evaluation board). Connecting the jumper to the external reference position enables an external reference source to be used.

Figure 2 shows the connections to implement a high side, bi-directional current sense with the ability to monitor the charging current. Figure 3 shows the connection for uni-directional ground referenced current sensing. The ISL28133 maintains precision performance from rail-to-rail making precision ground-side sensing possible.

R15

1.65V TO +5.5V

R13

4.7µF

100

C10 OPEN

R12A, B 1M

VS/2

REFERENCE

R10A, B 1M

JUMPER

EXT

REFERENCE

ISL28133

C4 1nF

R11

499k

V+

V-

R14

499k

5.6V

C20

OPEN

REF

SENSE

OUT

I-SENSE-

FIGURE 1. ISL28133 DIFFERENTIAL CURRENT SENSE AMPLIFIER

GND

AN1480.2

July 18, 2011

Page 3

CONNECT TO

EXTERNAL

POWER

Application Note 1480

CONNECT TO

BATTERY

POWER

1.65V TO +5.5V

I-SENSE+

JUMPER

EXT

REFERENCE

REF

VS/2

REFERENCE

SENSE

LOAD

CURRENT

FLOW

I-SENSE-

= +2.5V ±2.5V

OUT

SENSE

= +2.5V

REF

FOR = 0A ±0.25A

CHARGING

CURRENT

GND

SENSE

OUT

REF

FIGURE 2. CURRENT SENSE FOR HIGH-SIDE BI-DIRECTIONAL RE-CHARGEABLE BATTERY SUPPLY

CONNECT TO

BATTERY

EXTERNAL

POWER

1.65V TO +5.5V

POWER

I-SENSE+

OUT

SENSE

= 0V

REF

= 0V TO 5V

FOR

= 0A 0.5A

GND

SENSE

OUT

REF

JUMPER

EXT

REFERENCE

VS/2

REFERENCE

SENSE

CURRENT

FLOW

I-SENSE-

FIGURE 3. CURRENT SENSE FOR LOW SIDE UNI-DIRECTIONAL MEASUREMENT

LOAD

0V TO

+5.5V

AN1480.2

July 18, 2011

Page 4

Application Note 1480

ISL28133ISENSEV1Z Components Parts List

DEVICE # DESCRIPTION COMMENTS

C2 CAP-SMD, 0805, 4.7µF, 50V, 10%, X7R, ROHS Power supply decoupling

C4, C7, C9 CAP, SMD, 0603, 1000F, 25V, 10%, X7R, ROHS Power supply decoupling

C8 CAP, SMD, 0603, 0.1µF, 25V, 10%, X7R, ROHS Power supply decoupling

C10, C20 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS User-selectable capacitors - not populated

D1 Zener Diode ROHS Reverse power protection

D2- D4 DIODE-SCHOTTKY BARRIER, SMD, SOT-23, 3P, 40V, ROHS Reverse power protection

R13 RESISTOR, SMD, 0603, 0Ω, 1/16W, 0.1%, TF, ROHS 0Ω user selectable resistors

R1- R5 RES, SMD, 0805, 0.1Ω, 1/10W, 0.1%, TF, ROHS Current sense resistors

R6, R7 RES, SMD, 0805, 10Ω, 1/10W, 0.1%, TF, ROHS Protection resistors

R15 RES, SMD, 0805, 100Ω, 1/10W, 0.1%, TF, ROHS Protection resistors

R8, R9 RES, SMD, 0805, 4.99kΩ, 1/10W, 0.1%, TF, ROHS 0Ω user selectable resistors

R11, R14, R10A, R10B, R12A, R12B RES, SMD, 0805, 499kΩ, 1/10W, 0.1%, TF, ROHS Gain and other user selectable resistors

U1 (ISL28133FHZ-T7) IC-5 MHz, RRIO OP AMP, SOT23_5, ROHS

R1, R2, R4, R5 RES, SMD, 0805, DNP Optional sense resistors

AN1480.2

July 18, 2011

Page 5

Application Note 1480

ISL28133ISENSEV1Z Schematic Diagram

DNP

I-SENSE + I-SENSE J4 J5

R6 10

1000pF

DNP

0.10 R4

DNP

0.01µF D2

R7 10

1000pF

V-REF J1

R11

499k

R10B 499k

R10A 499k

R12B 499k

R12A 499k

4.99k

C20

OPEN

R14

499k

1 2

ISL28133

SOT23_5

4.7µF

1000pF

4.99k

R13

C10

OPEN

I-SENSE

OUT

J2 GND

R15 100

J3 VS1+

AN1480.2

July 18, 2011

Page 6

Application Note 1480

FIGURE 4. ISL28133ISENSEV1Z TOP VIEW

Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is

cautioned to verify that the Application Note or Technical Brief is current before proceeding.

For information regarding Intersil Corporation and its products, see www.intersil.com

AN1480.2

July 18, 2011