EVAL-AD5100EBZ View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

EVAL-AD5100EBZ

System Management IC with Factory Programmed Quad Voltage Monitoring and Supervisory Functions

Analog Devices 

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AD5100

PROTECTION

For automotive applications, proper external protections on the

AD5100 are needed to ensure reliable operation. The V1MON is

likely to be used for battery monitoring. The V2MON is likely to

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

these inputs may need additional protections such as EMI, load

dump, and ESD protections. In addition, battery input requires

reverse battery protection and short-circuit fuse protection (see

Figure 19).

Overcurrent Protection

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

short-circuit protection kicks in and limits subsequent current

to 150 mA in normal operation.

Thermal Shutdown

When the AD5100 junction temperature is near the junction

temperature limit, it automatically shuts down and cuts out the

power from V1MON. The part resumes operation when the device

junction temperature returns to normal.

ESD Protection

It is common to require a contact rating of ±8 kV and a no

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

automotive electronics. As a result, an ESD-rated protection

device must be used, such as MMBZ27VCL, a dual 40 W

transient voltage suppressor (TVS) 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

a resulting long duration, high voltage surge is introduced into

the supply line. Therefore, external load dump protection is

recommended. Typically, the load dump overvoltage lasts for a

few hundred milliseconds and peaks at around 40 V to 70 V,

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

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

surge energy. A series resistor is an inline 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.

Reverse Battery Protection

Reverse battery protection can be provided by a regular diode

if the battery monitoring accuracy can be relaxed. Otherwise,

a 60 V P-channel power MOSFET, like the NDT2955, can be

used. Because of the MOSFET internal diode, the battery first

conducts through the P1 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 is negligible. The resistor divider values are chosen such

that the maximum VGS of the P1 is not violated and the current

drawn through the battery is only a few microamps.

EMI Protection

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

as DR331-7-103, can be used.

C1

0.1µF

L1

10µH

NDT2955

DR331-7-103

P1

R3

2.2Ω

C3

10µF

D1

R1

2MΩ

VREG

EN

VREF

V1MON

F1

B+

L1

–

+

VMAIN

C2

0.1µF

R2

1.5MΩ

SMCJ17

DIGIPOT

IGNITION SWITCH

R4

2.2Ω

D2 D3 D4

V2MON

DIGIPOT

AD5100

SMCJ17

MMBZ27VCL

Figure 19. Protection Circuits

Rev. A | Page 22 of 36

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