EUP7559
Application Note
The EUP7559 is a high performance, low quiescent
current power management IC consisting of two µCap
low dropout regulators. The first regulator is capable of
sourcing 300mA at output voltages from 1.5V to 3.3V.
The second regulator is capable of sourcing 300mA of
current at output voltages from 1.5V to 3.3V. These
outputs are stable with 2.2uF output capacitor at any
load.
Enable A and B
The enable inputs allow for logic control of both output
voltages with individual enable inputs. The EUP7559 is
turned off by pulling the V
EN
pin low, and turned on by
pulling it high. If this feature is not used, the V
EN
pin
should be tied to V
IN
to keep the regulator output on at all
time. To assure proper operation, the signal source used
to drive the V
EN
input must be able to swing above and
below the specified turn-on/off voltage thresholds listed
in the Electrical Characteristics section under V
IL
and
V
IH
.
External Capacitors
Like any low-dropout regulator, the EUP7559 requires
external capacitors for regulator stability. The EUP7559
is specifically designed for portable applications
requiring minimum board space and smallest components.
These capacitors must be correctly selected for good
performance.
Input Capacitor
An input capacitance of
≈
2.2µF or greater is required
between the EUP7559 input pin and ground (the amount
of the capacitance may be increased without limit).
This capacitor must be located a distance of not more
than 1cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or
film capacitor may be used at the input.
Output Capacitor
The EUP7559 is designed specifically to work with
very small ceramic output capacitors. A ceramic
capacitor (temperature characteristics X7R, X5R,
Z5U, or Y5V) in 2.2µF to 22µF range with 5mΩ to
500mΩ ESR range is suitable in the EUP7559
application circuit.
The output capacitor must meet the requirement for
minimum amount of capacitance and also have an
ESR (Equivalent Series Resistance) value which is
within a stable range (5mΩ to 500mΩ)
No-Load Stability
The EUP7559 will remain stable and in regulation
with no external load. This is specially important in
CMOS RAM keep-alive applications.
Capacitor Characteristics
The EUP7559 is designed to work with ceramic
capacitors on the output ceramic capacitors are the
smallest, least expensive and have the lowest ESR
values (which makes them best for eliminating high
frequency noise). The ESR of a typical 2.2µF ceramic
capacitor is in the range of 10mΩ to 40mΩ, which
easily meets the ESR requirement for stability by the
EUP7559.
The ceramic capacitor’s capacitance can vary with
temperature. The capacitor type X7R, which operates
over a temperature range of -55°C to +125°C, will only
vary the capacitance to within ±15%. Most large value
ceramic capacitors (
≈
2.2µF) are manufactured with
Z5U or Y5V temperature characteristics. Their
capacitance can drop by more than 50% as the
temperature goes from 25°C to 85°C. Therefore, X7R
is recommended over Z5U and Y5V in applications
where the ambient temperature will change
significantly above or below 25°C.
Noise Bypass Capacitor
Connecting a 0.01µF capacitor between the BP pin and
ground significantly reduces noise on the regulator
output. This cap is connected directly to a high
impedance node in the bandgap reference circuit. Any
significant loading on this node will cause a change on
the regulated output voltage. For this reason, DC
leakage current through this pin must be kept as low as
possible for best output voltage accuracy. The types of
capacitors best suited for the noise bypass capacitor are
ceramic and film.
Unlike many other LDO’s, addition of a noise
reduction capacitor does not effect the load transient
response of the device.
DS7559 Ver 1.0 May. 2007
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
