ADM1070ART datasheet(13/16 Pages) AD

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REV. 0

ADM1070

–13–

CURRENT FAULT PLOTS

Some timing waveforms associated with current over faults are

shown in the following figures. Figure 9 shows how a current

glitch (of approximately 500

µs) is dealt with when the output is

shorted after power-up. The gate voltage is at a constant 12.3 V

before the glitch occurs. When the short circuit occurs, the

sense voltage rises sharply as the load current ramps up quickly.

When the sense voltage reaches 100 mV (VACL), the ADM1070

reduces the gate voltage to stop the load current from increasing

any further. When VSENSE drops back below VACL, the gate

voltage is increased again.

GATE

SENSE

VOUT

CH3

10.00V

CH1

20.00V

CH2

100mV

M 500 s

CH2

34mV

Figure 9. Timing Waveforms Associated with a

Current Glitch

The plots shown illustrate the operation of the ADM1070’s

unique limited consecutive retry function. Figure 10 highlights

what happens when a current fault occurs for more than 14 ms

(default tLIMITON when TIMER Pin tied to VEE) and a current

fault is registered. In this case, gate is previously low and the

part is being powered up into a current fault situation (shorted

load). When power is applied, gate is allowed to ramp until

sense reaches 100 mV. gate is then held constant to keep sense

at this level. After tON, the PWM cycle begins and gate is

reduced to zero.

5.00V

CH2

100mV M

5.00 s

CH1

1.4V

CH1

GATE

SENSE

14ms

Figure 10. Timing Waveforms Associated with a

Current Fault

Figure 11 shows a current fault on a wider timebase. The first

spike on the sense line represents the first current fault. The

sense voltage is allowed to ramp up to 100 mV before the gate

voltage is reduced to compensate. The gate and sense voltages

remain at these levels until the tON time has expired. A current

fault is then registered and the gate voltage, and therefore the

sense voltage, are then both held low for the time period tOFF.

Note that the PWM ratio (tON/tOFF) is equal to 3%. The cycle

then restarts and the sense voltage is free to ramp up to 100 mV

again (it will if the fault is still present). This cycle repeats itself

a total of seven times. Figure 12 shows the seven consecutive

faults occurring on an even wider timebase. If the ADM1070

detects seven consecutive current faults, the part then latches off

(after a total time tSHORT).

GATE

SENSE

5.00V

CH2

1.00V

CH3

100mV

M 100ms

CH1

tON

tOFF

Figure 11. Illustration of the PWM Ratio (tON/tOFF)

GATE

SENSE

5.00V

CH2

1.00V

CH3

100mV

M 100ms

CH1

tSHORT

Figure 12. Illustration of the Limited Consecutive

Retry Function (Seven Retries and Latch Off)

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