5.0 VOLT ULTRA LOW DROPOUT
REGULATOR
ISSUE 2 - JULY 1997
DEVICE DESCRIPTION
The ZLDO Series low dropout linear
regulators operate with an exceptionally
low dropout voltage, typically only 30mV
with a load current of 100mA. The regulator
series features output voltages in the range
2.7 to 18 volts, this device provides an output
voltage of 5.0 volts.
The ZLDO500 consumes a typical quiescent
current of only 1mA at its maximum rated
output current of 300mA. A battery low flag
is available to indicate potential power fail
situations. If the input voltage falls to within
200mV of the regulated output voltage then
the error output pulls low. The device also
features an active high disable control. Once
disabled the ZLDO quiescent current falls to
typically 11µA.
The ZLDO devices are packaged in Zetex
SM8 8 pin small outline surface mount
package, ideal for applications where space
saving is important. The device low dropout
voltage, low quiescent current and small size
make it ideal for low power and battery
powered applications. Battery powered
circuits can make particular use of the low
battery flag and shutdown features.
Low Battery Flag
ZLDO500
FEATURES
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Very low dropout voltage
6mV dropout at 10mA output
30mV dropout at 100mA output
100mV dropout at 300mA output
5.0 volt fixed output
Other voltages available
Low quiescent current
1mA quiescent at 300mA output
Low battery flag
Shutdown control
Surface mount package
APPLICATIONS
Battery powered devices
Portable instruments
Portable communications
Laptop/Palmtop computers
Electronic organisers
Vin
LOW BATTERY
COMPARATOR
THERMAL
SHUTDOWN
Vo
Shutdown
Control
SHUTDOWN
BIAS
CIRCUIT
OUTPUT
DRIVE
Cs
BANDGAP
REFERENCE
Shaping
Gnd
4-80
ZLDO500
NOTES.
1.
Maximum power dissipation of the device is calculated assuming the package is mounted on a
PCB measuring 2 inches square.
2
Output voltage temperature coefficient is calculated as:-
V
O
change x
1000000
V
O
x temperature change
3.
Dropout voltage is defined as the input to output voltage differential at which the circuit ceases
to regulate. The value is measured when the output voltage has dropped by 100mV from V
out
measured at the nominal input V
in
= V
out
+ 1V
4.
Guaranteed by design.
FUNCTIONAL DESCRIPTION
The ZLDO is a high performance, ultra low
dropout, low quiescent regulator. Available in
SM8 surface mount packaging, the device is
able to dissipate 2W(note 1) allowing
complete design flexibility with an input span
upto 20V and 300mA output current. The
device quiescent is 1mA (typ) at 300mA load
current. A low battery comparator signifies
PIN DEFINITIONS
Pin 1
LBF - Low Battery Flag. An open
collector NPN output which pulls low on failing
input supply.
Pin 2
SC - Shutdown Control. This high
impedance logic compatible input disables the
regulator when taken high. It includes a diode
wired to Vin and so will pass current if taken
more than 0.5V above Vin.
Pin 3
Vin - Voltage Input. The power supply to
the regulator. The permissible input voltage
range is -0.3 to 20V. An input capacitor is not
mandatory but will be useful in reducing the
coupling of noise from input to output and
minimising the effect of sudden changes in load
current on the input voltage.
Pin 4
N/C - Not Connected. Not internally
connected and so can be left open or wired to
any pin without affecting the performance of the
regulator.
Pin 5
Vout - Voltage Output. The output of the
regulator. An output capacitor of 1uF or greater
and having low ESR should be wired in close
proximity to the regulator to ensure stability for
all loads.
Pin 6
D/C - Do Not Connect. This pin is wired
to an internal circuit node of the regulator. No
external connection should be made to this pin.
Pin 7
Gnd - Ground. The ground connection
of the regulator against which the output
voltage is referenced.
Pin 8
Spg - Shaping. The shaping node for
the error amplifier of the regulator. A
capacitor of 10pF wired from this pin to the
output pin (pin 5) gives optimum stability.
Improved AC can be achieved by reducing
the value of this capacitor but stability may
be impaired for some load conditions.
impending battery failure, whilst a shutdown
function reduces quiescent current to a mere
11µA (typ). A precision bandgap reference
gives
±
2.5% output tolerance and good
temperature characteristics over the range
-40 to +85°C. AC performance is enhanced via
the use of a small external capacitor.
4-82
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