ZL9101M datasheet(13/63 Pages) RENESAS

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ZL9101M

FN7669 Rev.8.00

Page 13 of 63

Jun 20, 2017

2. Turn off the high-side MOSFET and turn on the low-side

MOSFET. The low-side MOSFET remains ON until the device

attempts a restart.

The default response from an overvoltage fault is to immediately

shut down. The controller continuously checks for the presence

of the fault condition and when the fault condition no longer

exists, the device is re-enabled.

For continuous overvoltage protection when operating from an

external clock, the only allowed response is an immediate

shutdown.

Output Prebias Protection

An output prebias condition exists when an externally applied

voltage is present on a power supply’s output before the power

supply’s control IC is enabled. Certain applications require that

the converter not be allowed to sink current during start-up if a

prebias condition exists at the output. The ZL9101M provides

prebias protection by sampling the output voltage prior to

initiating an output ramp.

If a prebias voltage lower than the target voltage exists after the

preconfigured delay period has expired, the target voltage is set

to match the existing prebias voltage and both drivers are

enabled. The output voltage is then ramped to the final

regulation value at the preconfigured ramp rate.

The actual time the output takes to ramp from the prebias

voltage to the target voltage varies, depending on the prebias

voltage, however, the total time elapsed from when the delay

period expires and when the output reaches its target value will

match the preconfigured ramp time (see Figure 15).

If a prebias voltage higher than the target voltage exists after the

preconfigured delay period has expired, the target voltage is set

to match the existing prebias voltage, and both drivers are

enabled with a PWM duty cycle that would ideally create the

prebias voltage.

After the preconfigured soft-start ramp period has expired, the

PG pin is asserted (assuming the prebias 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 prebias 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 12 for response options due to an overvoltage condition.

Note that prebias protection is not offered for current sharing

groups, which also have tracking enabled. VDD must be tied to

VIN for proper prebias start-up in single module operation.

Output Overcurrent Protection

The ZL9101M 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.

Thermal Overload Protection

The ZL9101M 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 can set the limit to a different value if desired. Note that setting

a higher thermal limit through the I2C/SMBus interface may result

in permanent damage to the controller. Once the module has been

disabled due to an internal temperature fault, the user can 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

FIGURE 15. OUTPUT RESPONSES TO PREBIAS VOLTAGES

DESIRED OUTPUT

VOLTAGE

PREBIAS

VOLTAGE

VOUT

TIME

TON-

DELAY

TON-

RISE

DESIRED OUTPUT

VOLTAGE

PREBIAS

VOLTAGE

VOUT

TIME

VPREBIAS < VTARGET

VPREBIAS > VTARGET

TON-

RISE

TON-

DELAY

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