AD5100EVAL datasheet(20/32 Pages) AD

20 / 32 page

AD5100

Preliminary Technical Data

Rev. PrJ | Page 20 of 32

Poor PCB layout introduces parasitic inductance that may affect

the fuse programming voltage droop. Therefore, it is mandatory

that a 10μF tantalum capacitor be placed as close as possible to

the VOTP pin. The value and the type of C2 chosen are

important. It should provide both a fast response and larger

supply current handling with minimum supply droop during

programming, see Figure 18.

Protection

Over-Current Protection

If the V1MON is shorted internally in the AD5100 to GND, the

short-circuit protection kicks in and limits subsequent current

to 150mA in normal operation or 50mA when the VOTP is

executed.

Thermal Shutdown

When the AD5100 junction temperature is near the junction

temperature limit, it will automatically shutdown and cut out

the power from V1MON. The part will resume operational when

the device junction temperature returns to normal.

For automotive applications, proper external protections on the

AD5100 are needed in order to ensure reliable operation. The

V1MON will likely be used for battery monitoring. The V2MON will

likely be used for ignition switch or other critical inputs. As a

result, these inputs may need additional protections such as

EMI, loaddump, and ESD protections. In addition, battery input

also requires reverse battery protection and short circuit fuse

protection, see Figure 19.

ESD Protection

It is common to require a contact rating of ±8kV and a non-

contact or air rating of ±15kV ESD protection for the

automotive electronics. As a result, a ESD rated protection

device must be used such as MMBV27VCL, a dual 40W TVS

(Transient Voltage Suppressor) at the V1MON and V2MON.

Load Dump Protection

A load dump is a severe overvoltage surge that occurs when the

car battery is being disconnected from a spinning alternator and

the resulting long-duration, high-voltage surge introduced into

the supply line. As a result, external load dump protection is

recommended. Typically the load dump overvoltage lasts for

few hundreds millisecond and peaks at around 40V to 70V

while current can be as high as 1A. As a result, a load dump

rated TVS D1 and D2 such as SMCJ17 are used to handle the

surge energy. A series R is an in-line current limiting resistor, it

should be adequate to limit the current without significant drop

and yet small enough to not affect the input monitoring

accuracy drop

Reverse Battery Protection

Reverse battery protection can be provided by a regular diode if

the battery monitoring accuracy can be relaxed. Otherwise, a

60V P-Ch Power MOSFET, like NDT2955, can be used. Because

of the MOSFET internal diode, the battery will first conduct

through P1’s body diode, as soon as the voltage reaches its

source terminal, the voltage divider provides adequate gate-to-

source voltage to turn on P1 and the voltage drop across the

FET will be negligible. The resistor divider values are chosen

such that the P1’s maximum VGS is not violated and the current

drawn through the battery is only a few μA.

EMI Protection

For EMI protection, ferrite bead or EMC rated inductor such as

DR331-7-103 can be used.

Figure 19. Protection Circuits

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