L4918 ,VOLTAGE REGULATORS PLUS FILTERELECTRICAL CHARACTERISTICS (T = 25 °C; V = 13.5 V, unless otherwise specified)amb iSymbol Paramete ..
L4920 ,VERY LOWDROP ADJUSTABLE REGULATORSL4920 L4921VERY LOW DROP ADJUSTABLE REGULATORS.VERY LOW DROP VOLTAGE. ADJUSTABLE OUTPUT VOLTAGE FR ..
L4921 ,VERY LOWDROP ADJUSTABLE REGULATORSapplications where low con-The outputvoltageisadjustablethroughanexternalsumption is particularly i ..
L4922 ,VERY LOW DROP REGULATOR WITH RESETL4922 VERY LOW DROP REGULATOR WITH RESET. VERY LOW DROP (max. 0.9 V at 1 A) OVERFULL OPERATING TEM ..
L4923 ,WITH RESET AND INHIBIT 5V.1A VERY LOW DROP REGULATORELECTRICAL CHARACTERISTICS (V = 14. 4V, – 40°C ≤ T ≤ + 125°C unless otherwise specified)i JSymbol P ..
L4925PD ,VERY LOW DROP VOLTAGE REGULATORL4925®VERY LOW DROP VOLTAGE REGULATOROPERATING DC SUPPLY VOLTAGE RANGE6V TO 28VTRANSIENT SUPPLY VOL ..
LB8555D ,General-Purpose TimerElectrical Characteristics at Ta = 25''C min typ max unitSupply Current IcCI Vcc= 5V,RL= 0° 3 6 mA. ..
LB8555M ,General-Purpose TimerAbsolute Maximum Ratings at Ta = 25''C unitMaximum Supply Voltage Vcc max 18 VOutput Current IOUT 1 ..
LB8555S ,General-Purpose TimerOrdering number: EN 1077CMonolithic Digital ICLB8555D, 8555SGeneral-Purpose TimerOverviewThe LB8555 ..
LB8620M ,Low-voltage/Low-saturation Bidirectional Motor DriverAbsolute Maximum Ratings at Ta = 25˚CPl arameter Ss ymbo Cs ondition Rt ating UniMaximum supply vol ..
LB8620M ,Low-voltage/Low-saturation Bidirectional Motor DriverElectrical Characteristics at Ta = 25˚CRatingsPl arameter Ss ymbo Condition Unitmp intx y maSupply ..
LB8632 ,Low-Voltage/Low-Saturation Camera Motor DriverOrdering number : EN5161ANo. 5161AOverviewThe L88632V is a general-purpose camera motor driverIC th ..
L4918
VOLTAGE REGULATORS PLUS FILTER
L4918October 1988
VOLTAGE REGULATORS PLUS FILTER
PRELIMINARY DATA. FIXED OUTPUT VOLTAGE 8.5V. 250mA OUTPUT CURRENT. HIGH RIPPLE REJECTION. HIGH LOAD REGULATION. HIGH LINE REGULATION. SHORT CIRCUIT PROTECTION. THERMAL SHUT DOWN WITH HYSTERESIS. DUMP PROTECTION
DESCRIPTIONThe L4918 combines both a filter and a voltage regu-
lator in order to provide a high ripple rejection over a
wider input voltage range.
A supervisor low-pass loop of the element prevents
the output transistor from saturation at low input vol
tages.
The non linear behaviour of this control circuitry al-
lows a fast setting of the filter.
BLOCK DIAGRAM1/6
ABSOLUTE MAXIMUM RATINGS
PIN CONNECTION (top view)
Figure 1 : Application and Test Circuit.
THERMAL DATA
L49182/6
ELECTRICAL CHARACTERISTICS (Tamb = 25 °C; Vi = 13.5 V, unless otherwise specified)(*) Depending of the CFT capacitor
PRINCIPLE OF OPERATIONDuring normal operation (input voltage upper than
VI MIN = VOUT NOM + ΔVI/O). The device works as a
normal voltage regulator built around the OP1 of the
block diagram.
The series pass element use a PNP-NPN connec-
tion to reduce the dropout. The reference voltage of
the OP1 is derived from a REF through the OP2 and
Q3, acting as an active zener diode of value VREF.
In this condition the device works in the range (1) of
the characteristic of the non linear drop control unit
(see fig.2).
The output voltage is fixed to its nominal value: R1VOUT NOM = VREF (1 + ) = VCFT (1 + )R2 R2 = INTERNALLY FIXED RATIO = 2.4R2
The ripple rejection is quite high (71 dB) and inde-
pendent from CFT value.
On the usual voltage regulators, when the input volt-
age goes below the nominal value, the regulation
transistors (series element) saturate bringing the
system out of regulation making it very sensible to
every variation of the input voltage. Onthe contrary,
a control loop on the L4918 consents to avoid the
saturation of the series element by regulating the
value of the reference voltage (pin 2). In fact, when-
ever the input voltage decreases below VI MIN the su-
pervisor loop, utilizing a non linear OTA, forces the
reference voltage at pin 2 to decrease by discharg-
ing CFT. So, during the static mode, when the input
voltage goes below VMIN the drop out is kept fixed
to about 1.6 V. In this condition the device works as
a low pass filter in the range (2) of the OTA charac-
L49183/6
teristic. The ripple rejection is externally adjustable
acting on CFT as follows:
VI (jw) SVR (jw) = =
Vout (jw)–6
1 + R1 (1 + ) jwCFT R2
Where:
gm = 2 . 10-5 Ω-1 = OTA’S typical transconductance
value on linear region = fixed ratio
CFT = value of capacitor in μF
The reaction time of the supervisor loop is given by
the transconductance of the OTA and by CFT. When
the value of the ripple voltage is so high and its nega-
tive peak is fast/enough to determine an istantane-
ous decrease of the dropout till 1.2V, the OTA works
in a higher transconductance condition [range (3) of
the characteristic] and discharge the capacitor rapi-
dously.
If the ripple frequency is high enough the capacitor
won’t charge itself completely, and the output vol-
tage reaches a small value allowing a better ripple
rejection; the device’s again working as a filter (fast
transient range).
With CFT = 10 μF ; f = 100 Hz a SVR of 35 is obtained.
Figure 2 : Nonliner Transfer Characteristic of the
Drop Control Unit.
Figure 3 : Supply Voltage Rejection vs. Fre-
Figure 4 : Supply voltage Rejection vs. Input Volt-
age.
Figure 5 : Output Voltage vs. Input Voltage.
L49184/6
PENTAWATT PACKAGE MECHANICAL DATA
L49185/6
. However, SGS-THOMSON Microelectronics assumes no responsibility for
the or other rights of third parties which may result from its
use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifica-
tions mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information pre-
viously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or
systems without express written approval of SGS-THOMSON Microelectronics.
© 1994 SGS-THOMSON Microelectronics - All Rights Reserved
SGS-THOMSON Microelectronics GROUP OF COMPANIES
Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore -
Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.
L49186/6
