30
FN6849.3
December 16, 2011
6 Power Management Functional Description
6.1 Input Undervoltage Lockout (UVLO)
Standard Mode
The input undervoltage lockout (UVLO) prevents the
ZL2005P from operating when the input falls below a
preset threshold, indicating the input supply is out of its
specified range. The UVLO threshold (V
UVLO
) can be
set between 2.85 V and 16 V using the UVLO pin. The
simplest implementation is to connect the UVLO pin as
shown in Table 25. If the UVLO pin is left uncon-
nected, the UVLO threshold will default to 4.5 V.
Table 25. UVLO Threshold Settings
LOW 3 V
OPEN 4.5 V
HIGH 10.8 V
If the desired UVLO threshold is not one of the listed
choice
s, the user can configure a threshold between
2.85 V and 16 V by connecting a resistor between the
UVLO pin and GND by selecting the appropriate
resistor from Table 26.
Table 26. UVLO Resistor Values
2.85 V 17.8 kΩ 7.42 V 46.4 kΩ
3.14 V 19.6 kΩ 8.18 V 51.1 kΩ
3.44 V 21.5 kΩ 8.99 V 56.2 kΩ
3.79 V 23.7 kΩ 9.9 V 61.9 kΩ
4.18 V 26.1 kΩ 10.9 V 68.1 kΩ
4.59 V 28.7 kΩ 12 V 75 kΩ
5.06 V 31.6 kΩ 13.2 V 82.5 kΩ
5.57 V 34.8 kΩ 14.54 V 90.9 kΩ
6.13 V 38.3 kΩ 16 V 100 kΩ
6.75 V 42.2 kΩ
V
UVLO
can also be set to any value between 2.85 V
and 16 V via I
2
C/SMBus.
Once an input undervoltage fault condition
occurs, the
device can respond in a number of ways as follows:
1. Continue operating wit
hout interruption.
2. Continue operating for a given delay time, fol-
lowed by shutdown if the fault still persists at the
end of the delay period. The devi
ce will remain in
shutdown until permitted to restart.
3. Initiate an immediate shutdown until the fault has
been
cleared. The user can select a specific num-
ber of retry attempts.
The default response from a
UVLO fault is an imme-
diate shutdown of the device. The
device will continu-
ously check for the presence of the fault condition. If
the
fault condition is no longer present, the ZL2005P
will be re-enabled.
Please refer to Application Note AN2013 for details
on
how to configure the UVLO threshold or to select
specific UVLO fault response options via the I
2
C/
SMBus interface.
6.2 Output Overvoltage Protection
The ZL2005P 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. This feature is especially
useful in protecting expensive processors, FPGAs, and
ASICs from excessive voltages.
A hardware comparator is used to compare the actual
ou
tput voltage (seen at the VSEN pin) to a threshold set
to 15% higher than the target output voltage by default.
If the voltage at the VSEN pin exceeds this upper
threshold level, the PG pin will de-assert. 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 num-
ber 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 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
ZL2005P will be re-enabled.
Please refer to Application Note AN2013 for details
on how to sele
ct specific overvoltage fault response
options via the I
2
C/SMBus interface.
Pin Setting UVLO Threshold
UVLO R
UVLO
UVLO R
UVLO
ZL2005P
