STMICROELECTRONICS L4915

L4915
ADJUSTABLE VOLTAGE REGULATOR PLUS FILTER
.
..
..
..
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PRELIMINARY DATA
OUTPUT VOLTAGE ADJUSTABLE FROM
4 TO 11V
HIGH OUTPUT CURRENT (up to 250mA)
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 wide input voltage range.
A supervisor low-pass loop of the element prevents
the output transistor from saturation at low input
voltage.
The non linear behaviour of this control circuitry
allows a fast settling of the filter.
POWER MINIDIP
ORDERING NUMBER : L4915
PIN CONNECTION
June1993
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L4915
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Symbol
Vi
Vi
IO
Ptot
Tstg
Parameter
Peak Input Voltage (300 ms)
DC Input Voltage
Output Current
Power Dissipation
Storage and Junction Temperature
Value
40
28
Internally Limited
Internally Limited
– 40 to 150
Unit
V
V
Value
80
20
Unit
°C/W
°C/W
°C
THERMAL DATA
Symbol
Rth j-amb
R th j-pins
Parameter
Thermal Resistance Junction-ambient
Thermal Resistance Junction-pins
Max.
Max.
ELECTRICAL CHARACTERISTICS
(Tamb = 25oC; Vi = 13.5 V, VO = 8.5V, circuit of Fig. 1, unless otherwise specified)
Symbol
Vi
Vo
∆VI/O
∆VO
∆Vo
2/7
Parameter
Input Voltage
Output Voltage
Controlled Input-output Dropout Voltage
Line Regulation
Load Regulation
∆Vo
Load Regulation (filter mode)
Vref
Iq
∆Iq
IAD
Internal Voltage Reference
Quiescent Current
Quiescent Current Change
Adjust Input Current
Test Conditions
Vi = 6 to 18V, Io = 5 to 150mA
Io = 5 to 150mA, Vi = 6 to 10V
Vi = 12 to 18V, Io = 10mA
Io = 5 to 250mA,
ton = 30µs, toff = ≥ 1ms
Vi = 8.5V, Io = 5 to 150mA
ton = 30µs, toff =≥ 1ms
Io = 5 mA
Vi = 6 to 18V, Io = 5 to 150mA
Min.
Typ.
1.6
1
50
Max.
20
11
2.1
20
100
Unit
V
V
V
mV
mV
150
250
mV
4
2.5
1
0.05
40
2
V
mA
mA
nA
L4915
ELECTRICAL CHARACTERISTICS (continued)
(Tamb = 25oC; Vi = 13.5 V, VO = 8.5V, circuit of Fig. 1, unless otherwise specified)
Symbol
∆VO
∆T
SVR
ISC
Ton
Tj
Parameter
Test Conditions
Output Voltage Drift
Io = 10mA
Supply Voltage Rejection
Viac = 1VRMS, f = 100Hz, Io = 150mA
Regulator
Filter Mode
Short Circuit Current
Switch On Time
Min.
1.2
Max.
Unit
mV/°C
dB
250
Io = 150mA
Regulator
Filter Mode
Thermal Shutdown Junction
Temperature
Typ.
71
35(*)
300
300
500(*)
145
mA
ms
°C
(*) Depending of the CFT capacitor
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 around the OP1 of
the block diagram.
The series pass element uses 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 Figure 1).
Figure 1 :
Nonliner Transfer Characteristic of
the Drop Control Unit
the contrary, a control loop on the L4915 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 1.6 V. 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 (jΩ) 
10−6

SVR (jΩ) = 
=1+

R1  
 gm 
 VOUT (jΩ) 
1
+


 jw C
R2  
FT 

Where:
gm = 2 ⋅ 10-5 Ω-1
= OTA’S typical transconductance value on
linear region
R1 = fixed ratio
R2
CFT = value of capacitor in µF
The output voltage is fixed to its nominal value :
R1 


R1 
VOUT NOM = VREF  1 +
 = VCFT  1 + R2 
R2




The ripple rejection is quite high (70dB) and independent to CFT value.
On the usual voltage regulators, when the input
vol-tage goes below the nominal value, the regulation transistors (series element) saturate bringing
the system out of regulation and making it very
sensible to every variation of the input voltage. On
The reaction time of the supervisor loop is given by
the transconductanceof the OTAand 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 1.2V, the OTA
works in a higher transconductance condition
[range (3) of the characteristic] and discharges 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 better ripple
rejection ; the device’s again working as a filter (fast
transient range).
With CFT = 10µF; f = 100Hz; Vo = 8.5V a SVR of 35
is obtained.
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L4915
Figure 2 :
Supply Voltage Rejection versus
Input Voltage
Figure 3 :
Supply Voltage Rejection versus
Frequency
Figure 4 :
VO versus Supply Voltage (VO = 8.5V)
Figure 5 :
Quiescent Current versus
Input Voltage (VO = 8.5V)
Figure 6 :
Dropout versus Load Current
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L4915
APPLICATION CIRCUIT
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L4915
MINIDIP 4+4 PACKAGE MECHANICAL DATA
mm
DIM.
MIN.
A
TYP.
MAX.
MIN.
3.3
TYP.
MAX.
0.130
a1
0.7
B
1.39
1.65
0.055
0.065
B1
0.91
1.04
0.036
0.041
b
b1
0.028
0.5
0.38
0.020
0.5
D
0.015
0.020
9.8
0.386
E
8.8
0.346
e
2.54
0.100
e3
7.62
0.300
e4
7.62
0.300
F
7.1
0.280
I
4.8
0.189
L
Z
6/7
inch
3.3
0.44
0.130
1.6
0.017
0.063
L4915
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 inlife support devices or systems without express
written approval of SGS-THOMSON Microelectronics.
 1994 SGS-THOMSON Microelectronics - All Rights Reserved
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