Preliminary
EUP7211
DS7211 Ver 0.3 Nov. 2005
9
Application Note
Function Description
The EUP7211 is a high performance, low quiescent current
power management IC consisting of two µCap low dropout
regulators, a power-on reset (POR) circuit and an open-drain
driver. The first regulator is capable of sourcing 150mA at
output voltages from 1.25V to 5V. The second regulator is
capable of sourcing 300mA of current at output voltages
from 1.25V to 5V. The second regulator has a POR circuit
that monitors its output voltage and indicates when the
output voltage is within 5% of nominal. The POR offers a
delay time that is externally programmable with a single
capacitor to ground. An open-drain driver completes the
power management chipset, offering the capability of
driving LEDs for keypad backlighting in applications such
as cellphones.
Enable 1 and 2
The enable inputs allow for logic control of both output
voltages with individual enable inputs. The EUP7211 is
turned off by pulling the VEN pin low, and turned on by
pulling it high. If this feature is not used, the VEN pin should
be tied to VIN to keep the regulator output on at all time. To
assure proper operation, the signal source used to drive the
VEN input must be able to swing above and below the
specified turn-on/off voltage thresholds listed in the
Electrical Characteristics section under VIL and VIH.
External Capacitors
Like any low-dropout regulator, the EUP7211 requires
external capacitors for regulator stability. The EUP7211 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
≈ 1µF or greater is required
between the EUP7211 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 EUP7211 is designed specifically to work with very
small ceramic output capacitors. A ceramic capacitor
(temperature characteristics X7R, X5R, Z5U, or Y5V) in 1
to 22µF range with 5mΩ to 500mΩ ESR range is suitable in
the EUP7211 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 EUP7211 will remain stable and in regulation with no
external load. This is specially important in CMOS RAM
keep-alive applications.
Capacitor Characteristics
The EUP7211 is designed to work with ceramic capacitors
on the output to take advantage of the benefits they offer:
for capacitance values in the range of 1µF to 4.7µF range,
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 1µF
ceramic capacitor is in the range of 20mΩ to 40mΩ, which
easily meets the ESR requirement for stability by the
EUP7211.
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 CBYPASS 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
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