AD8450ASTZ datasheet(28/42 Pages) AD

28 / 42 page

Data Sheet

AD8450

Rev. B | Page 27 of 41

OVERCURRENT AND OVERVOLTAGE

COMPARATORS

The AD8450 includes overcurrent protection (OCP) and over-

voltage protection (OVP) comparators to detect overvoltage

and overcurrent conditions in the battery. Because the outputs

of the comparators are combined by a NOR logic gate, these

comparators output a logic low at the FAULT pin when either

comparator is tripped (see Figure 49).

The OCP and OVP comparators can be configured to detect a

fault in one of two ways. In the configuration shown in Figure 56,

the voltages at the ISMEA and BVMEA pins are divided down

and compared to the internal 2.5 V reference of the AD8450. In

this configuration, the FAULT pin registers a logic low (a fault

condition) when

VISMEA >

R1+

× 2.5 V

VBVMEA >

R3 +

× 2.5 V

–

OCPS

OCPR

OVPR

VREF

FAULT

OVPS

BVPx

BVNx

ISMEA

BVMEA

ISVP

ISVN

–

PGIA

–

PGDA

NOR

Figure 56. OVP and OCP Comparator Configuration

Using the Internal Reference

Alternatively, the outputs of the PGIA and PGDA can be tied

directly to the sense inputs of the comparators (OCPS and

OVPS pins) such that the voltages at the ISMEA and BVMEA

pins are compared to the external reference voltages, VOCP_REF

and VOVP_REF (see Figure 57). In this configuration, the FAULT

pin registers a logic low (a fault condition) when

VISMEA > VOCP_REF

VBVMEA > VOVP_REF

–

OCPS

OCPR

OVPR

FAULT

OVPS

BVPx

BVNx

ISMEA

BVMEA

ISVP

ISVN

–

PGIA

–

PGDA

NOR

–+

VOVP_REF

VOCP_REF

Figure 57. OVP and OCP Comparator Configuration

Using an External Reference (For Example, a DAC)

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