1.5A Very L.D.O Voltage Regulator
LM27150/27151/27152
Capacitor Requirements
For stability and minimum output noise, a capacitor on the regulator output is necessary. The value of this
capacitor is dependent upon the output current; lower currents allow smaller capacitors. LM27150
regulators are stable with the 10uF minimum capacitor values at full load. Where the regulator is powered
from a source with a high AC impedance, a 0.1uF capacitor connected between input and GND is
recommended. This capacitor should have good characteristics to above 250kHz.
Minimum Load Current
The LM27150 regulators are specified between finite loads. If the output is too small, leakage currents is too
small, leakage currents dominate and the output voltage rises. The 5mA minimum load current swamps any
expected leakage current across the operating temperature range.
Adjustable Regulator Design
The adjustable regulator versions, LM27152 allows programming the output voltage anywhere between
1.25V and the 25V maximum operating rating of the family.
Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the very high input impedance
and low bias current of the sense comparator: The resistor values are calculated by:
R1=R2(
V
OUT
‐
1)
V
REF
Where V
OUT
is desired output voltage, Figure 2 shows component definition. Applications with widely
varying load currents may scale the resistors to draw the minimum load current required for proper
operation.
V
IN
+
C
IN
VIN
EN
GND
OUT
R1
V
OUT
+
C
OUT
R2
ADJ
V
OUT
= 1.240 x [1 + (R1/R2)]
Figure 2. Adjustable Regulator with Resistors
Error Flag
LM27151 versions feature and Error Flag, which looks at the output voltage and signals and error condition
when this voltage and signals an error condition when this voltage drops 5% below its expected value. The
error flag is an open-collector output that pulls low under fault conditions. It may sink 10mA. Low output
voltage signifies a number of possible problems, including an over-current fault (the device is in current
limit) and low input voltage. The flag output is inoperative during over temperature shutdown conditions.
Dec. 2011 – Rev.1.3.1
-
10
-
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
