ISL78171 Datasheet, PDF(17/29 Page) Intersil Corporation – 6-Channel, 50mA Automotive LED Driver with Ultra-high Dimming Ratio and Phase Shift Control

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ISL78171 Datasheet, PDF (17/29 Pages) Intersil Corporation – 6-Channel, 50mA Automotive LED Driver with Ultra-high Dimming Ratio and Phase Shift Control

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VIN

FAULT

DRIVER

IMAX

ILIMIT

LOGIC

ISL78171

O/P

SHORT

FET

DRIVER

OVP

VSC

VOUT

CH0

VSET/2

CH5

REG

THRM

SHDN

REF

OTP

TEMP

SENSOR

VSET +

Q0 VSET +

FAULT/

STATUS

SMBUS/I2C

CONTROL

LOGIC

PWM/OC0/SC0

DC CURRENT

PWM/OC5/SC5

FIGURE 29. SIMPLIFIED FAULT PROTECTIONS

TABLE 2. PROTECTIONS TABLE

CASE FAILURE MODE

DETECTION MODE

FAILED CHANNEL ACTION

GOOD CHANNELS ACTION

VOUT REGULATED

1 CHx Short Circuit

Upper Over-Temperature CHx ON and burns power.

Protection limit (OTP) not

triggered and CHx < 7.5V

Remaining channels normal

Highest VF of all

channels

2 CHx Short Circuit

3 CHx Short Circuit

Upper OTP triggered but

CHx < 7.5V

Upper OTP not triggered

but CHx > 7.5V

All channels go off until chip cooled

and then comes back on with

current reduced to 76%. Subsequent

OTP triggers will reduce IOUT further.

Same as CHx

CHx disabled after 6 PWM cycle

time-outs.

Remaining channels normal

Highest VF of

remaining

channels

Highest VF of

remaining

channels

4 CHx Open Circuit with Upper OTP not triggered VOUT will ramp to OVP. CHx will

infinite resistance and CHx < 7.5V

time-out after 6 PWM cycles and

Remaining channels normal

switch off. VOUT will drop to normal

level.

Highest VF of

remaining

channels

5 CHx LED Open Circuit Upper OTP not triggered CHx remains ON and has highest VF, Remaining channels ON,

but has paralleled

Zener

and CHx < 7.5V

thus VOUT increases.

remaining channel FETs burn

power

VF of CHX

6 CHx LED Open Circuit Upper OTP triggered but All channels go off until chip cooled Same as CHx

but has paralleled CHx < 7.5V

and then comes back on with

Zener

current reduced to 76%. Subsequent

OTP triggers will reduce IOUT further

VF of CHx

7 CHx LED Open Circuit Upper OTP not triggered CHx remains ON and has highest VF, VOUT increases, then CH-X

VF of CHx

but has paralleled but CHx > 7.5V

thus VOUT increases.

switches OFF after 6 PWM cycles.

Zener

This is an unwanted shut off and

can be prevented by setting OVP

at an appropriate level.

Submit Document Feedback 17

FN8602.0

June 15, 2015

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