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L4916
VOLTAGE REGULATOR PLUS FILTER
. . . . . . . .
PRELIMINARY DATA
FIXED OUTPUT VOLTAGE 8.5 V 250 mA OUTPUT CURRENT HIGH RIPPLE REJECTION HIGH LOAD REGULATION HIGH LINE REGULATION SHORT CIRCUIT PROTECTION THERMAL SHUT DOWN WITH HYSTERESIS DUMP PROTECTION
DESCRIPTION This circuit combines both a filter and a voltage regulator 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 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
October 1988
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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 R th j-amb R th j-pins Parameter Thermal Resistance Junction-ambient 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, test circuit of fig. 1, unless otherwise specified)
Symbol Vi VO VI/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 µs toff = 1 ms Vi = 8.5 V IO = 5 to 150 mA ton = 30 µs 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 capacitor.
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 regulator built 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 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.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 usual voltage 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, wheneverthe input voltagedecreases 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 jwCFT 10-6 (1 + R1 R2 )
Where: gm = 2 . 10-5 -1 = OTA'S typical transconductance value on linear region R1 = fixed ratio R2 = value of capacitor in µF CFT 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 ofthe dropout till 1.2 V, the OTA works in a higher transconductancecondition [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 reaches a small value allowing a betterripple 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.
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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 : Supply Voltage 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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MINIDIP 4+4 PACKAGE MECHANICAL DATA
DIM. 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 mm 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.
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Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics 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 SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously 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.
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