ZL9117M

10

FN7914.1

October 21, 2011

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 is asserted (assuming the pre-bias voltage is not higher

than the overvoltage limit). The PWM then adjusts its duty cycle

to match the original target voltage, and the output ramps down

to the preconfigured output voltage.

If a pre-bias voltage higher than the overvoltage limit exists, the

device does not initiate a turn-on sequence and declares an

overvoltage fault condition to exist. In this case, the device

responds based on the output overvoltage fault response method

that has been selected. See “Output Overvoltage Protection” on

page 9 for response options due to an overvoltage condition.

Note that pre-bias protection is not offered for current sharing

for proper prebias start-up in single module operation.

Output Overcurrent Protection

The ZL9117M can protect the power supply from damage if the

output is shorted to ground or if an overload condition is imposed

on the output. 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 controller. The controller continuously checks for

the presence of the fault condition, and if the fault condition no

longer exists, the device is re-enabled.

Please refer to Application Note AN2033 for details on how to

Thermal Overload Protection

The ZL9117M includes a thermal sensor that continuously

measures the internal temperature of the module and shuts

down the controller when the temperature exceeds the preset

limit. The default temperature limit is set to +125°C in the

factory, but the user may set the limit to a different value if

desired. See Application Note AN2033 for details. Note that

result in permanent damage to the controller. Once the module

has been disabled due to an internal temperature fault, the user

may select one of several fault response options as follows:

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.

If the user has configured the module to restart, the controller

waits the preset delay period (if configured to do so) and then

checks the module temperature. If the temperature has dropped

below a threshold that is approximately +15°C lower than the

selected temperature fault limit, the controller attempts to

re-start. If the temperature still exceeds the fault limit, the

controller waits the preset delay period and retries again.

The default response from a temperature fault is an immediate

shutdown of the module. The controller continuously checks for

the fault condition, and once the fault has cleared, the ZL9117M

is re-enabled.

Please refer to Application Note AN2033 for details on how to

select specific temperature fault response options via

Each module must have its own unique serial address to

distinguish between other devices on the bus. The module

address is set by connecting a resistor between the SA pin and

SGND. Table 2 lists the available module addresses.

FIGURE 13. OUTPUT RESPONSES TO PRE-BIAS VOLTAGES