High speed, Low dropout, ±1% High output accuracy Dual CMOS Voltage Regulator
Rev. E13-01
VRD Series
DESCRIPTION OF OPERATION
General operation
In reference to following a part of the block diagram of output voltage control of the VRD series ;
*1)
V
IN
Over-current
Protector
R
1
V
FEEDBACK
R
DIS
V
OUT
+
Voltage V
REF
Reference
R
2
Error Amp.
_
V
SS
EN
By the error amplifier, the reference voltage (V
REF
) is compared with V
FEEDBACK
which is divided by
feedback resistors R
1
and R
2
. It supplies the output transistor (see note *1) to keep a stabilized output
voltage against with any fluctuation of input voltage by negative feedback system.
Note *1)
The VRD series has P-channel MOSFET which is connected to the V
OUT
terminal as the output
transistor. To prevent the VRD series from being damaged due to inverse current from V
OUT
terminal to V
IN
terminal through a parasitic diode, V
OUT
should not be exceeded V
IN
+0.3V.
EN terminal (shutdown function) & C
L
auto-discharge
The VRD series can be shutdown through EN terminal. The P-channel MOSFET is turned off and
operation of all internal circuits stops to reduce the current consumption when the signal of EN
terminal is set to the shutdown level. In shutdown mode, the VRD series enables the electric charge at
the C
L
to be discharged via the auto-discharge resistance (R
DIS
; 160Ω), and the V
OUT
terminal can be
rapidly returned to the V
SS
level as a result.
Output capacitor (C
L
)
For phase compensation, an output capacitor (C
L
) is required to connected between V
OUT
terminal and
V
SS
terminal as close as possible. A ceramic capacitor with capacitance value of at least 1.0µF is
recommended. Of course, the suitable capacitance value should be different by the condition of each
application. In addition, an input capacitor (C
IN
) with capacitance value of at least 1.0µF is also
recommended between V
IN
terminal and V
SS
terminal for stable input power.
Over current protection and short circuit protection
Built-in over current protection circuit performs circuit protection from over current as a current limiter.
When the load current reaches the limit level, the output voltage drops and output current also
decreases accordingly. A current of typ. 40mA will flow when output terminal is shorted.
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