EUP7907
where VREF is the internal reference voltage, which is
0.8V in EUP7907.
Function Description
The EUP7907 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
2.2uF ceramic capacitor can make the device stable over
the whole load range.
As shown in the function block diagram, the EUP7907
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.
Figure 4. Output Voltage Select Circuit
Current Limit
The EUP7907 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 keep the current flowing to the
output. The typical value is 0.9A.
Thermal Shutdown
The EUP7907 monitor its temperature automatically.
When the operation junction temperature exceeds 170℃,
the OTP circuit starts the thermal shutdown function to
turn the pass transistor off until it cooled down by 30℃
then the pass transistor turned on again. For continue
operation, do not exceed absolute maximum operation
junction temperature. The circuit is a non-latched
protection.
Supply Input Power on Reset
The input voltage supplies current to the output and the
operation voltage of the internal circuit. The input
voltage is monitored for power on reset (POR) to ensure
the regulator is disabled when the input voltage is not
high enough for normal operation. The POR threshold
voltage is 2.1V at VIN rising typically.
Enable/Shutdown
The EUP7907 is disabled when the EN pin is connected
to ground or the voltage less than 0.4V, reducing the
quiescent current to less than 1uA. In the shutdown
mode the error amplifier, the reference voltage, the
driver and the pass transistor are all disabled. Make this
pin higher than 1.5V to enable the device.
Soft Stop
When the regulator is disabled, an internal 400Ω resistor
is connected between VOUT and GND. This is intended to
discharge COUT. The internal resistor is not used when
the device turns on.
Adjustable Output Voltage
EUP7907 has a wide output voltage range. The output
voltage is programmed using an external resistor divider
as shown in Figure 4. The output voltage can be
calculated by the following equation:
R
R2
VOUT = (1+ 1 )× VREF
(EQ. 1)
DS7907 Ver 1.1 Oct . 2008
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
