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(R)
L4916
VOLTAGE REGULATOR PLUS FILTER
.FI .250mAOUTPUTCURRENT .HI .HI .HI .SHORTCI .THERMALSHUTDOWNWI .DUMPPROTECTI
XED OUTPUT VOLTAGE 8.5 V GH RIPPLE REJECTION GH LOAD REGULATION GH LINE REGULATION RCUIT PROTECTION TH HYSTERESIS ON
DESCRIPTION This circuit combinesboth a filter and a voltageregulator in order to provide a high ripple rejection over a wider input voltage range. A supervisor low-pass loop of the element prevents the outputtransistor from saturationat low input voltages. The non linear behaviour of this control circuitry allows a fast settling of the filter. BLOCK DIAGRAM
POW ER MINIDIP (4 + 4)
ORDERING NUMBER : L4916
June 2000
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PIN CONNECTION (top view)
ABSOLUTE MAXIMUM RATINGS
Symbol Vi Vi IO Ptot Tstg, Tj Peak Input Voltage (300 ms) DC Input Voltage Output Current Power Dissipation Storage and Junction Temperature Parameter Value 40 28 Internally Limited Internally Limited - 40 to 150 C Unit V V
THERMAL DATA
Symbol Parameter R th j-amb Thermal Resistance Junction-ambient Rth j-pins Thermal Resistance Junction-pins Max Max Value 80 20 Unit C/W C/W
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ELECTRICAL CHARACTERISTICS (Tamb =25 C; Vi = 13.5 V, testcircuit of fig. 1, unlessotherwise specified)
Symbol Vi VO V I/O VO VO Parameter Input Voltage Output Voltage Controlled Voltage Vi = 12 to 18 V IO = 5 to 150 mA 8.1 8.5 1.6 1 50 Test Conditions Min. Typ. Max. 20 8.9 2.1 20 100 Unit V V V mV mV
Input-output Dropout Vi = 5 to 10 V IO = 5 to 150 mA Vi = 12 to 18 V IO = 10 mA IO = 5 to 250 mA ton = 30 s toff = 1 ms Vi = 8.5 V IO = 5 to 150 mA ton = 30 s toff = 1 ms IO = 5 mA Vi = 6 to 18 V IO = 5 to 150 mA IO = 10 mA Viac = 1 Vrms f = 100 Hz IO = 150 mA VIDC = 12 to 18 V VIDC = 6 to 11 V 250 IO = 150 mA Vi = 5 to 11 V Vi = 11 to 18 V Junction
Line Regulation Load Regulation
VO
Load Regulation (filter mode)
150
250
mV
Iq Iq VO T SVR
Quiescent Current Quiescent Current Change Output Voltage Drift Supply Voltage Rejection
1 0.05 1.2
2
mA mA mV/C
70 35(*) 300 500(*) 300 145
dB dB mA ms ms C
ISC Ton
Short Circuit Current Switch On Time
TJ
Thermal Shutdown Temperature
( *) D epending of the C FT capaci tor.
Figure 1 : Test and Application Circuit.
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Figure 2 : P.C. Board and Component Layout of Fig. 1 (1 : 1 scale).
PRINCIPLE OF OPERATION During normal operation (input voltage upper than VI MIN = VOUT NOM + VI/O). The device works as a normal voltage regulatorbuilt aroundthe OP1 of the block diagram. The series pass element use a PNP-NPN connection to reduce the dropout. The reference voltage of the OP1 is derived from a REF throughthe OP2and Q3, acting as an active zener diode of value VREF. In this conditionthe device works in the range (1) of the characteristic of the non linear drop control unit (see fig.3). The output voltage is fixed to its nominal value: R1 VOUT NOM = VREF (1 + )= R2 VCFT (1 + R1 ) R2 R1 = INTERNALLY FIXED RATIO = 2.4 R2 The ripple rejection is quite high (70 dB) and independent from CFT value. On the usualvoltage regulators, when the input voltage 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. On the contrary, a control loop on the L4916 consents to avoid the saturation of the series element by regulating the value of the reference voltage (pin 2). In fact, whenever the input voltage decreases below VI MIN the supervisor loop, utilizing a non linear OTA, forces the reference voltage at pin 2 to decrease by discharging CFT. So, during the static mode, when the
input voltage goes below VMIN the drop out is kept fixed to about 1.6V. In this condition the device works as a low pass filter in the range (2) of the OTA characteristic. The ripple rejection is externally adjustable acting on CFT as follows : VI (jw) SVR (jw) = = Vout (jw) 1+ gm Where: jwCFT 10-6 (1 + R1 R2 )
gm = 2 . 10-5 -1 = OTA'S typical transconductance value on linear region R1 = fixed ratio R2 CFT = value of capacitor in F The reaction time of the supervisor loop is given by the transconductanceof the OTA and by CFT. When the value of the ripple voltage is so high and its negative peak is fast enough to determine an istantaneous decrease of the dropout till 1.2 V, the OTA works in a higher transconductance condition [range (3) of the characteristic] and discharge the capacitor rapidously. If the ripple frequency is high enough the capacitor won't charge itself completely, and the output voltage reachesa small value allowinga betterripple rejection ; the device's again working as a filter (fast transient range). With CFT = 10 F; f = 100Hz a SVR of 35is obtained.
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Figure 3 : Nonliner Transfer Characteristic of the Drop Control Unit.
1) Normal operating range (high ripple rejection) 2) Drop controlled range (medium ripple rejection) 3) Fast discharge of CFT
Figure 4 : SupplyVoltage Rejection vs. Input Voltage.
Figure 5 : Supply voltage Rejection vs. Frequency.
Figure 6 : Vo vs. Supply Voltage.
Figure 7 : Quiescent Current vs. Input Voltage.
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Figure 8 : Dropout vs. Load Current.
Figure 9 : Inhibit Function Realized on CFT Pin.
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mm MIN. A a1 B B1 b b1 D E e e3 e4 F I L Z 0.44 3.3 1.6 0.017 8.8 2.54 7.62 7.62 7.1 4.8 0.130 0.063 0.38 0.7 1.39 0.91 0.5 0.5 9.8 0.346 0.100 0.300 0.300 0.280 0.189 0.015 1.65 1.04 TYP. 3.3 0.028 0.055 0.036 0.020 0.020 0.386 0.065 0.041 MAX. MIN. inch TYP. 0.130 MAX.
DIM.
OUTLINE AND MECHANICAL DATA
PowerMinidip
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Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents 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 STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c) 2000 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. http://www.st.com
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