EUP7907A
Current Limit
Function Description
The EUP7907A 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.
The EUP7907A 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
EUP7907A 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.
Thermal Shutdown
The EUP7907A 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 EUP7907A 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. If this pin
of EUP7907A is floating, the regulator on/off is unstable.
To assure proper operation the EN should be pulled
higher than the level listed in the Electrical
Characteristics section.
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.
DS7907A Ver 1.1 M ar. 2009
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
