ZLDO485
output impedance of the switching power
supply but no higher. The low dropout voltage
of the ZLDO485 allows this circuit technique to
be implemented very effectively, giving a
highly stable and accurate low noise supply.
3). Logic Controlled Power Supply
Fig.3 shows all that is necessary to allow a
microprocessor to control a power supply
based on the ZLDO485 The Shutdown Control
pin (pin 2), is a logic compatible input that
disables the regulator when a voltage in excess
of 1.5V is applied. The current required to drive
this input is less than 10µA. When the regulator
is shutdown in this way, the quiescent current
of the ZLDO485 falls to around 11µA. This
makes the regulator suitable for a wide range
of battery powered applications where
intermittent operation occurs. The shutdown
control pin should not be taken to a voltage
higher than Vin if low quiescent supply current
is important. The shutdown control is a high
impedance input and so if not required, should
be wired to the ground pin (pin 7).
4). Over Temperature Shutdown
The ZLDO485 regulator includes an over
temperature shutdown circuit that disables the
regulator if its chip temperature should exceed
125°C for any reason. Although intended to
provide a limited guard against excessive
internal power dissipation, this circuit will shut
down the regulator if its ambient rises above
125°C. Thus, the regulator could be used to
disable a circuit in the event of the ambient
temperature within which the circuit is
mounted becoming too high. Any internal
power dissipation caused as a result of
supplying load current, will reduce the
ambient temperature at which shutdown
occurs. Note that to achieve the extremely low
dropout voltage and high current performance
provided by the ZLDO485 devices, the parts
can be damaged by sustained output shorts or
excessive loads when combined with high
input supply voltages. To ensure reliable
operation, keep loads within the SOA graph
boundaries Indicated in the typical
characteristics.
APPLICATIONS
Spg
D/C
Vout
LBF
SC
Vin
N/C
Gnd
IC2
ZLDO485
C2
1uF
C1
10pF
C3
100nF
0V
+ 4.85V
Microproc.
System
Switched
Supply Input
Vin Vout
Gnd
IC1
ZSR500
Output
0V
+6.7V
to 20V
Figure 3
4-77
