ZL2004 datasheet(28/42 Pages) RENESAS

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ZL2004

FN6846 Rev. 3.00

Page 28 of 42

February 15, 2011

6. Power Management Functional Description

6.1 Input Undervoltage Lockout

The input undervoltage lockout (UVLO) prevents the

ZL2004 from operating when the input falls below a

preset threshold, indicating the input supply is out of

its specified range. The UVLO threshold (VUVLO) can

be set between 4.5V and 10.8 V using the SS pin. The

simplest implementation is to connect the SS pin as

shown in Table 11.

The UVLO voltage can also be set to any value

between 2.85 V and 16 V via the I

2C/SMBus interface.

Once an input undervoltage fault condition occurs, the

device can respond in a number of ways as follows:

1. Continue operating without interruption.

2. Continue operating for a given delay period,

followed by shutdown if the fault still exists. The

device will remain in shutdown until instructed to

restart.

3. Initiate an immediate shutdown until the fault has

been cleared. The user can select a specific number

of retry attempts.

The default response from a UVLO fault is an

immediate shutdown of the device. The device will

continuously check for the presence of the fault

condition. If the fault condition is no longer present,

the ZL2004 will be re-enabled.

Please refer to Application Note AN33 for details on

how to configure the UVLO threshold or to select

specific

UVLO

fault

response

options

via

the

2C/SMBus interface.

6.2 Output Overvoltage Protection

The ZL2004 offers an internal output overvoltage

protection circuit that can be used to protect sensitive

load circuitry from being subjected to a voltage higher

than its prescribed limits. A hardware comparator is

used to compare the actual output voltage (seen at the

VSEN pin) to a threshold set to 15% higher than the

target output voltage (the default setting). If the VSEN

voltage exceeds this threshold, the PG pin will de-

assert and the device can then respond in a number of

ways as follows:

1. Initiate an immediate shutdown until the fault has

been cleared. The user can select a specific number

of retry attempts.

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 device will continuously

check for the presence of the fault condition, and when

the fault condition no longer exists the device will be

re-enabled.

For continuous overvoltage protection when operating

from an external clock, the only allowed response is an

immediate shutdown.

Refer to AN33 for details on how to select specific

overvoltage fault response options.

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.

Certain applications require that the converter not be

allowed to sink current during start up if a pre-bias

condition exists at the output. The ZL2004 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 output

voltage is then ramped to the final regulation value at

the ramp rate set by the SS pin.

ZL2004 Datasheet(PDF) 28 Page - Renesas Technology Corp

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