EUP7903
Detailed Function Description
The EUP7903 is a high output current, low dropout
linear regulator with fast transient response and high
PSRR. It offers high output accuracy, extremely low
dropout voltage, low quiescent current and fast start-up
time. It is designed to work with low-ESR ceramic
capacitor, reducing the amount of the PCB area. Only a
1uF ceramic capacitor can make the device stable over
the whole load range.
As shown in the function block diagram, the EUP7903
is composed of the bandgap reference voltage, the error
amplifier, P-channel MOSFET pass transistor, internal
resistor divider and some additional protection circuits.
The reference voltage, connected to the cathode
terminal of the error amplifier, compares with the
feedback voltage to regulate the output voltage to make
it constant over the whole load range. If the feedback
voltage is lower than the reference voltage, the pass
transistor gate is pulled low to increase its conductivity.
This allows more current to flow to the output and
increases the output voltage. If the feedback voltage is
higher than the reference voltage, the pass transistor
allows less current to flow to the output. The feedback
point is the output of the internal or external resistor
divider connected to the VOUT pin.
Enable/Shutdown
The EUP7903 is disabled when the EN pin is connected
to ground or the voltage less than 0.4V, and the
quiescent current is less than 1uA. Connect EN pin to
1.5V or higher to enable the device.
Output Soft stop
When the regulator is disabled, an internal 400Ω resistor
is connected between V
OUT
and GND. To discharge
output capacitor C
OUT
.
Adjustable Output Voltage
EUP7903 has a wide output voltage range. The output
voltage is programmed by an external resistor divider as
shown in Figure 1. The output voltage can be calculated
by the following equation:
Figure. 4 Output Voltage Select Circuit
Fixed Output Voltage
When the FB voltage is less than 220mV, EUP7903 will
operate in the fixed output mode, its output is one of
pre-set values: 1.25V~5V. There is no external
component needed to set the output voltage.
Current Limit
The EUP7903 includes a current limit circuit to monitor
the gate voltage of the pass transistor to limit the output
current. When the output current is higher than the
over-current limit, the circuit will clamp the gate voltage
of the pass transistor to limit the output current. The
typical output current limit is 500mA.
Thermal Shutdown
The EUP7903 monitors internal temperature. When the
junction temperature exceeds 155℃, the over
temperature protection (OTP) circuit turn off the pass
transistor until the device is cooled down by 30℃. Then
the pass transistor resumes. For continue operation, do
not exceed absolute maximum junctiqwk iknf on
temperature.
Application Information
Resistor Select
Choose R2=100k to optimize accuracy, power supply
rejection, noise and power consumption. And the R1 can
be chosen by:
R
1
=
R
2
(
V
OUT
=
(1
+
R
1
)
×
V
REF
R
2
V
OUT
−
1)
V
REF
(EQ.2)
(EQ.1)
Where V
REF
is the internal reference voltage, which is
1.25V in EUP7903.
where V
REF
is the internal reference voltage, which is
1.25V in EUP7903.
External Capacitor
The EUP7903 requires external capacitors for stability.
It is specifically designed to work with low-ESR
capacitors requiring minimum PCB area.
Input capacitor
A 1uF ceramic capacitor or higher is required between
the VIN pin and the GND pin. Place it as close as
possible to the device. There are no requirements for the
ESR on the input capacitor, but the tolerance and
temperature coefficient must be considered when
selecting the capacitor to ensure the capacitance is 1uF
over the whole operating temperature range.
DS7903
Ver 1.0
Nov. 2008
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
