AD8452 datasheet(30/35 Pages) AD

30 / 35 page

Data Sheet

AD8452

Rev. 0 | Page 29 of 34

POWER SUPPLY CONNECTIONS

The AD8452 requires three analog power supplies (AVCC, VIN,

and AVEE). Two separate ground pins, AGND and DGND,

provide options for isolating analog and digital ground paths in

high noise environments. In most applications, however, these

two pins can be connected to a common ground.

AVCC and AVEE power all the analog blocks, including the

in-amp, difference amplifier, and op amps. VIN powers an internal

5 V LDO regulated supply (VREG) that powers the mode logic

and PWM.

The rated absolute maximum value for AVCC − AVEE is 36 V,

and the minimum operating AVCC and AVEE voltages are +10 V

and −26 V, respectively. Due to the high PSRR of the AD8452

analog circuitry, the AVCC pin can be connected directly to the

high current power bus (the input voltage of the power converter)

without risking injection of supply noise to the controller outputs.

A commonly used power supply combination is +12 V for

AVCC and −5 V for AVEE. The 12 V rail for AVCC provides

enough headroom to the in-amp such that it can be connected

in a high-side current sensing configuration. The −5 V AVEE

rail allows the difference amplifier output to become negative if

the battery under test (BUT) is accidentally connected in

reverse. The condition can be detected by monitoring BVMEA

for reverse voltage.

It is good practice to connect decoupling capacitors to all the

supply pins. A 1 µF ceramic capacitor in parallel with a 0.1 µF

capacitor is recommended.

CURRENT SENSE IN-AMP CONNECTIONS

For a description of the instrumentation amplifier, see the

Theory of Operation section, Figure 33, and Figure 35. The

in-amp fixed gain is 66 V/V.

Current Sensors

Two common options for current sensors are isolated current

sensing transducers and shunt resistors. Isolated current sensing

transducers are galvanically isolated from the power converter

and are affected less by the high frequency noise generated by

switch mode power supplies. Shunt resistors are far less

expensive, easier to deploy and generally more popular.

If a shunt resistor sensor is used, a 4-terminal, low resistance shunt

resistor is recommended. Two of the four terminals conduct the

battery current, whereas the other two terminals conduct virtually

no current. The terminals that conduct no current are sense

terminals that are used to measure the voltage drop across the

resistor (and, therefore, the current flowing through it) using an

amplifier such as the in-amp of the AD8452. To interface the

in-amp with the current sensor, connect the sense terminals of

the sensor to the ISVP pin and ISVN pin of the AD8452 (see

Figure 50).

Optional Low-Pass Filter

Due to the extremely high impedance of the instrumentation

amplifier used for a current shunt amplifier, power stage

switching noise can become an issue if the input circuitry is in

close proximity to the power stage components. This issue is

mitigated by shielding the input leads with ground potential

shielding designed into the PCB artwork and keeping the input

leads close together between the current sense shunt and the

input pins.

Connecting an external differential low-pass filter between the

current sensor and the in-amp inputs is also an effective method to

reduce the injection of switching noise into the in-amp (see

Figure 50).

ISVP

10kΩ

20kΩ

4-TERMINAL

SHUNT

IBAT

BATTERY

UNTER TEST

ISVN

10kΩ

305Ω

IMEAS

–

OPT

LPF

Figure 50. 4-Terminal Shunt Resistor Connected to the Current Sense In-Amp

VOLTAGE SENSE DIFFERENTIAL AMPLIFIER

CONNECTIONS

For a description of the difference amplifier, see the Theory of

Operation section, Figure 33, and Figure 36. The gain of the

difference amplifier is fixed at 0.4×. For AD8452 applications in

large installations, the best practice is to connect each battery

with a dedicated pair of conductors to avoid accuracy issues.

This recommendation applies whether using wiring harnesses

or a distributed PCB approach (mother/ daughter boards) to the

system design.

BATTERY CURRENT AND VOLTAGE CONTROL

INPUTS (ISET AND VSET)

The voltages at the ISET pin and the VSET pin set the target

battery current and voltage (CC mode and CV mode) and

require highly accurate and stable voltages to drive them. For a

locally controlled system, a low noise LDO regulator such as the

ADP7102ARDZ-5.0 is appropriate. For large scale computer

controlled systems, a digital-to-analog converter (DAC) such as

the dual channel, 16-bit AD5689RBRUZ is suitable for these

purposes. In either event, the source output voltage and the in-amp

and difference amplifier reference pins (ISREFH/ISREFL and

BVREFH/BVREFL, respectively) must use the same ground

reference. For example, if the in-amp reference pins are connected

to AGND, the voltage source connected to ISET must also be

referenced to AGND. In the same way, if the difference amplifier

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