zl2005 Intersil Corporation, zl2005 Datasheet - Page 30

• Manufacturer Part Number: zl2005
• Description: Digital-dc? Integrated Power Management And Conversion Ic
• Manufacturer: Intersil Corporation

6.3 Output Pre-Bias Protection
An output pre-bias condition exists when an externally
applied voltage is present on a power supply’s output
before the power supply’s control IC is enabled. Cer-
tain applications require that the converter not be
allowed to sink current during start up if a pre-bias
condition exists at the output. The ZL2005 provides
pre-bias protection by sampling the output voltage
prior to initiating an output ramp.
If a pre-bias voltage lower 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. The out-
put voltage is then ramped to the final regulation value
at the ramp rate set by the SS (0,1) pins. 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 16.
I
Figure 16. Output Response to Pre-Bias
Pre-bias
Pre-bias
voltage
voltage
voltage
voltage
Target
Target
V
V
OUT
OUT
Delay
SS
Delay
V
V
SS
PREBIAS
PREBIAS
Voltages
< V
> V
Ramp
30
SS
TARGET
TARGET
Ramp
SS
Delay
PG
Time
Time
ZL2005
If the pre-bias voltage is 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.
period has expired, the Power Good 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 out-
put voltage.
If a pre-bias voltage higher than the overvoltage limit,
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 over-
voltage fault response method that has been selected.
See Section 6.2, “Output Overvoltage Protection,” for
response options due to an overvoltage condition.
6.4 Output Overcurrent Protection
The ZL2005 can protect the power supply from dam-
age 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 5.9,
“Current Limit Threshold Selection,” ), the user may
determine the desired course of action to be taken
when an overload condition exists.
The following overcurrent protection response options
are available:
1. Initiate a shutdown and attempt to restart an infi-
2. Initiate a shutdown and attempt to restart the
3. Continue operating throughout a specific delay
4. Continue operating throughout the fault (this
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 condi-
tion. If the fault condition is no longer present, the
ZL2005 will be re-enabled.
nite number of times with a preset delay time.
power supply a preset number of times with a pre-
set delay between attempts.
time, followed by shutdown.
could result in permanent damage to the power
supply).
Once the pre-configured soft-start ramp
February 18, 2009
FN6848.0