ZL2004 datasheet(29/42 Pages) RENESAS

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ZL2004

FN6846 Rev. 3.00

Page 29 of 42

February 15, 2011

Figure 17. Output Responses to Pre-bias Voltages

The actual time the output will take to ramp from the

pre-bias voltage to the target voltage will vary

depending on the pre-bias voltage but the total time

elapsed from when the delay period expires and when

the output reaches its target value will match the pre-

configured ramp time. See Figure 17.

If a pre-bias voltage higher than the target voltage

exists after the pre-configured delay period has

expired, the target voltage is set to match the existing

pre-bias voltage and both drivers are enabled with a

PWM duty cycle that would ideally create the pre-bias

voltage. Once the pre-configured soft-start ramp period

has expired, the PG pin will be asserted (assuming the

pre-bias voltage is not higher than the overvoltage

limit). The PWM will then adjust its duty cycle to

match the original target voltage and the output will

ramp down to the pre-configured output voltage.

If a pre-bias voltage higher than the overvoltage limit

exists, the device will not initiate a turn-on sequence

and will declare an overvoltage fault condition to exist.

In this case, the device will respond based on the

output overvoltage fault response method that has been

selected.

See

Section

6.2

“Output Overvoltage

Protection,” for response options due to an overvoltage

condition.

Pre-bias protection is not offered for current sharing

groups that also have tracking enabled.

6.4 Output Overcurrent Protection

The ZL2004 can protect the power supply from

damage if the output is shorted to ground or if an

overload condition is imposed on the output. Once the

current limit threshold has been selected (see Section

5.8 “Current Limit Threshold Selection”), the user may

determine the desired course of action in response to

the

fault

condition.

The

following

overcurrent

protection response options are available:

1. Initiate a shutdown and attempt to restart an

infinite number of times with a preset delay period

between attempts.

2. Initiate a shutdown and attempt to restart a preset

number of times with a preset delay period

between attempts.

3. Continue operating for a given delay period,

followed by shutdown if the fault still exists.

4. Continue operating through the fault (this could

result in permanent damage to the power supply).

5. Initiate an immediate shutdown.

The default response from an overcurrent fault is an

immediate shutdown of the device. The device will

continuously check for the presence of the fault

condition, and if the fault condition no longer exists the

device will be re-enabled.

Refer to AN33 for details on how to select specific

overcurrent fault response options.

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