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LT1431 Programmable Reference
U
5V V + RTOP REF - RMID 2.5V LT1431 GND-S
LT1431 * TA01
FEATURES
s s s s s
DESCRIPTIO
Guaranteed 0.4% Initial Voltage Tolerance 0.1 Typical Dynamic Output Impedance Fast Turn-On Sink Current Capability, 1mA to 100mA Low Reference Pin Current
APPLICATI
s s s
S
Linear Regulators Adjustable Power Supplies Switching Power Supplies
The LT1431 is an adjustable shunt voltage regulator with 100mA sink capability, 0.4% initial reference voltage tolerance, and 0.3% typical temperature stability. On-chip divider resistors allow the LT1431 to be configured as a 5V shunt regulator, with 1% initial voltage tolerance and requiring no additional external components. By adding two external resistors, the output voltage may be set to any value between 2.5V and 36V. The nominal internal current limit of 100mA may be decreased by including one external resistor. A simplified three pin version, the LT1431Z/IZ, is available for applications as an adjustable reference and is pin compatible with the TL431.
TYPICAL APPLICATI
+
VIN
SWITCHING REGULATOR + gm = 4mA/V
-
UO
UO
Isolated 5V Regulator
+
COLL
COMP
GND-F
1
LT1431 ABSOLUTE AXI U RATI GS
JunctionTemperature Range LT1431M ........................................ - 55C to 150C LT1431I .......................................... - 40C to 100C LT1431C ............................................. 0C to 100C Storage Temperature Range ................ -65C to 150C Lead Temperature (Soldering, 10 sec)................ 300C
V+, VCOLLECTOR ....................................................... 36V VCOMP, RTOP,RMID,VREF ............................................ 6V GND-F to GND-S .................................................... 0.7V Ambient Temperature Range LT1431M ........................................ - 55C to 125C LT1431I ............................................ - 40C to 85C LT1431C .............................................. 0C TO 70C
PACKAGE/ORDER I FOR ATIO
TOP VIEW COLLECTOR 1 COMP 2 V+ 3 RTOP 4 J8 PACKAGE 8-LEAD CERAMIC DIP 8 7 6 5 REF RMID GND-F GND-S
ORDER PART NUMBER
COLLECTOR 1
LT1431MJ8 LT1431CN8 LT1431IN8
COMP 2 V+ 3 RTOP 4
N8 PACKAGE 8-LEAD PLASTIC DIP
S8 PACKAGE 8-LEAD PLASTIC SOIC
TJ MAX = 150C, JA = 100C/W (J) TJ MAX = 100C, JA = 130C/W (N)
TJ MAX = 100C, JA = 170C/W
ELECTRICAL CHARACTERISTICS TA = 25C, IK = 10mA, unless otherwise specified (Note 1).
SYMBOL
VREF VREF/T
PARAMETER
Reference Voltage Reference Drift
CONDITIONS
VKA = 5V, IK = 2mA, (Note 2)
q
VKA = 5V, IK = 2mA IK = 2mA, VKA = 3V to 36V VKA = 5V, TA = 25C
VREF/VKA Voltage Ratio, Reference to Cathode (Open-Loop Gain) |IREF| IMIN |IOFF| |ILEAK| |ZKA| ILIM Reference Input Current Minimum Operating Current Off-State Cathode Current Off-State Collector Leakage Current Dynamic Impedance Collector Current Limit 5V Reference Output
VKA = VREF to 36V VKA = 36V, VREF = 0V
q
VCOLL = 36V, V + = 5V, VREF = 2.4V
q
VKA = VREF, IK = 1mA to 100mA, f 1kHz VKA = VREF + 50mV Internal Divider Used, IK = 2mA
q
The q denotes specifications which apply over the operating temperature range. Note 1: VKA is the cathode voltage of the LT1431CZ/IZ and corresponds to V + of the LT1431CN8/MJ8. IK is the cathode current of the LT1431CZ/IZ and corresponds to I(V +) + ICOLLECTOR of the LT1431CN8/MJ8/IN8.
2
U
U
W
WW
U
W
TOP VIEW 8 7 6 5 REF RMID GND-F GND-S
ORDER PART NUMBER LT1431CS8 LT1431IS8 PART MARKING LT1431 LT1431I
BOTTOM VIEW 3 2 1
ORDER PART NUMBER LT1431CZ LT1431IZ
REF ANODE CATHODE
Z PACKAGE 3-LEAD TO-92 PLASTIC
TJ MAX = 100C, JA = 160C/W
LT1431M/I MIN TYP MAX
LT1431C MIN TYP MAX UNITS
V V ppm/C 0.5 1.0 1.2 1.0 1 2 1 2 0.2 100 260 mV/V A A mA A A A A mA V
2.490 2.500 2.510 2.490 2.500 2.510 2.465 2.535 2.480 2.520 50 0.2 0.2 0.5 1.0 1.5 1.0 1 15 1 5 0.2 80 360 30 0.2 0.2 0.6
q q
q
0.6
4.950 5.000 5.050 4.950 5.000 5.050
Note 2: The LT1431 has bias current cancellation which is effective only for VKA 3V. A slight (2mV) shift in reference voltage occurs when VKA drops below 3V. For this reason, these tests are not performed at VKA = VREF.
LT1431
TYPICAL PERFOR A CE CHARACTERISTICS
2.5V Reference IK vs VKA
1000 900 800 700 IMIN 2.505 2.504 2.503 2.502
VREF (V)
IK (A)
600 500 400 300 200 100 0 0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VKA (V)
LT1431 * TPC01
VREF and IREF vs V +
2.505 2.504 2.503 2.502 3.5 3.0 2.5 2.0
VREF (V)
2.5000 2.4975 2.5025
VREF (V)
2.501 2.500 2.499 2.498 2.497 2.496 2.495 0 4 8 12 16 20 24 28 32 36 40 V + (V)
LT1431 * TPC03
ILIMIT vs Temperature with External Resistor
1.250 ILIMIT = 1.125
ILIMIT (NORMALIZED)
0.7 AT 25C RLIM + 3.6
ICOLL = 100mA 1.000
VSAT (V)
PROPAGATION DELAY (s)
0.875 0.750 0.625 0.500 -50 -25
50 25 75 0 TEMPERATURE (C)
UW
IREF
100
VREF and IREF vs V +
3.5 3.0 2.5 2.0 VREF 1.5 1.0 0.5 0 -0.5 -1.0
2.501 2.500 2.499 2.498 2.497 2.496
IREF (A)
IREF
-1.5 2.495 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 + (V) V
LT1431 * TPC02
VREF and IREF vs Temperature
1.00 VREF 0.66 0.33
1.5 VREF 1.0 0.5 0 -0.5 -1.0 -1.5
COLLECTOR VSAT vs Temperature vs Current
1.20 1.00 0.80 0.60 ICOLL = 50mA 0.40 0.20 0 -50 -25 ICOLL = 20mA ICOLL = 10mA 50 25 75 0 TEMPERATURE (C) 100 125
150 135 120 105 90 75 60 45 30 15 0
IREF (A)
IREF (A)
2.4950 2.4925 2.4900 2.4875 -50 -25
IREF
0
-0.33 -0.66 -1.00 125
50 25 75 0 TEMPERATURE (C)
100
LT1027 * TPC04
Propagation Delay vs Overdrive
5V 1k 3 VREF OVERDRIVE LT1431 5 6 1 OUTPUT
OUTPUT HIGH-TO-LOW OUTPUT LOW-TO-HIGH
125
0
50
150 100 OVERDRIVE (mV)
200
250
LT1431 * TPC05
LT1431 * TPC06
LT1431 * TPC07
3
LT1431
TYPICAL PERFOR A CE CHARACTERISTICS
Voltage Gain and Phase vs Frequency
140 120
REF-TO-COLL 1k LOAD AV (dB)
PHASE AV
REF-TO-COLL gm (m )
100 80 60 40 20 0 -20 100
1k
10k 100k FREQUENCY (Hz)
Transconductance and Phase vs Frequency (Ref to Comp)
104 PHASE gm 0 -20 -40 103 -60 -80 3 x 102
1.2 1.0
REF-TO-COLL gm ( )
3 x 103
ZKA ()
0.8 0.6 0.4 0.2 0 100
VCOMP (V)
0.1 100
1k
10k 100k FREQUENCY (Hz)
ICOMP vs VCOMP vs VREF
600 500 VREF = 5V ICOMP (A) VREF = 4V VREF = 3V 200 VREF = 2.53V 100 0 0 0.5 1.0 1.5 2.0 VCOMP (V) 2.5 3.0 3.5
0 NOISE (nV/Hz) 1000
400 300
500
1
10
100 1k FREQUENCY (Hz)
10k
100k
NOISE VOLTAGE (50V/DIV)
4
UW
1M
Transconductance and Phase vs Frequency (REF to COLL)
180 135 90 45 0 -45 -90 -135 1M -180 10M
PHASE (DEG)
1010 10
9
180 135 PHASE 90 gm 45 0 -45 -90 -135 1k 10k 100k FREQUENCY (Hz) 1M -180 10M
108 107 106 105 104 103 102 100
PHASE (DEG)
LT1431 * TPC08
LT1431 * TPC09
Dynamic Impedance vs Frequency
20
1.4 IK 100mA
2.5 2.0 1.5 1.0 0.5 3.0
VCOMP vs Temperature vs ICOLL
-100 -120 -140 10M
PHASE (DEG)
ICOLL = 100mA ICOLL = 10mA
1k 10k FREQUENCY (Hz)
100k
LT1431 * TPC11
0 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
LT1431 * TPC10
LT1431 * TPC12
Noise vs Frequency
0.1Hz to 10Hz Noise
0
1
4 3 2 TIME (MINUTES)
5
6
LT1431 * TPC13
LT1431 * G14
LT1431 * TPC15
LT1431
PI FU CTIO S
COLL (Pin 1): Open collector of the output transistor. The maximum pin voltage is 26V. The saturation voltage at 100mA is approximately 1V. COMP (Pin 2): Base of the driver for the output transistor. This pin allows additional compensation for complex feedback systems and shutdown of the regulator. It must be left open if unused. V + (Pin 3): Bias voltage for the entire shunt regulator. The maximum input voltage is 36V and the minimum to operate is equal to VREF (2.5V). The quiescent current is typically 0.6mA. RTOP (Pin 4): Top of the on-chip 5k-5k resistive divider that guarantees 1% accuracy of operation as a 5V shunt regulator with no external trim. The pin is tied to COLL for self-contained 5V operation. It may be left open if unused. See note on parasitic diodes below. GND-S (Pin 5): Ground reference for the on-chip resistive divider and shunt regulator circuitry except for the output transistor. This pin allows external current limit of the output transistor with one resistor between GND-F (force) and GND-S (sense). GND-F (Pin 6): Emitter of the output transistor and substrate connection for the die. RMID (Pin 7): Middle of the on-chip resistive divider string between RTOP and GND-S. The pin is tied to REF for selfcontained 5V operation. It may be left open if unused. REF (Pin 8): Control pin of the shunt regulator with a 2.5V threshold. If V + > 3V, input bias current cancellation reduces IB to 0.2A typical. COMP, RTOP, RMID, and REF have static discharge protection circuits that must not be activated on a continuous basis. Therefore, the absolute maximum DC voltage on these pins is 6V, well beyond the normal operating conditions. As with all bipolar ICs, the LT1431 contains parasitic diodes which must not be forward biased or else anomalous behavior will result. Pin conditions to be avoided are RTOP below RMID in voltage and any pin below GND-F in voltage (except for GND-S). The following pin definitions apply to the Z package. CATHODE (Pin 1): Corresponds to COLL and V + tied together. ANODE (Pin 2): Corresponds to GND-S and GND-F tied together. REF (Pin 3): Corresponds to REF.
BLOCK DIAGRA
W
U
U
U
RTOP 4
V
+ 3
COMP 2
COLLECTOR 1
5k REF 8 + gm = 4mA/V -
RMID
7
5k
2.5V
5 GND-SENSE
6 GND-FORCE
LT1431 * BD01
5
LT1431
APPLICATIO S I FOR ATIO
Frequency Compensation
As a shunt regulator, the LT1431 is stable for all capacitive loads on the COLL pin. Capacitive loading between 0.01F and 18F causes reduced phase margin with some ringing under transient conditions. Output capacitors should not be used arbitrarily because output noise is not necessarily reduced. Excess capacitance on the REF pin can introduce enough phase shift to induce oscillation when configured as a reference >2.5V. This can be compensated with capacitance between COLL and REF (phase lead). More complicated feedback loops may require shaping of the frequency response of the LT1431 with dominant pole or
TYPICAL APPLICATIO S
2.5V Reference 3-Pin Package
RL VIN CATHODE REF LT1431Z ANODE
LT1431 * TA02
2.5V
VIN V+ LT1431 GND-S GND-F
LT1431 * TA03
Increasing 5V Reference
RL VIN R V+ RTOP LT1431 RMID GND-S GND-F
LT1431 * TA05
5V + COLL REF
= R x (0.5mA) 25% PROCESS TOLERANCE 500mV
6
U
pole-zero compensation. This can be accomplished with a capacitor or series resistor and capacitor between COLL and COMP. The compensation schemes mentioned above use voltage feedback to stabilize the circuits. There must be voltage gain at the COLL pin for them to be effective, so the COLL pin must see a reasonable AC impedance. Capacitive loading of the COLL pin reduces the AC impedance, voltage gain, and frequency response, thereby decreasing the effectiveness of the compensation schemes, but also decreasing their necessity.
2.5V Reference 8-Pin Package
RL 2.5V COLL REF
W
U
UU
5V Reference
RL VIN V+ RTOP LT1431 RMID GND-S GND-F
LT1431 * TA04
5V COLL REF
Programmable Reference with Adjustable Current Limit
RL VIN V+ LT1431 GND-S RLIM GND-F ILIMIT = 0.7 AT 25C RLIM + 3.6
LT1431 * TA06
VOUT = 1 + R1 VREF R2 COLL REF R2 R1
()
LT1431
TYPICAL APPLICATIO S
PNP Low Dropout 5V Regulator*
VIN 0.1F 20** 2W 1k 2N2219 0.015F 150 2 COMP V+ LT1431 RTOP GND-S 5 RMID GND-F 6 5V MEASURED DROPOUT VOLTAGE 420mV AT 4A 190mV AT 2A 95mV AT 1A 60mV AT 0.5A *NO SHORT-CIRCUIT PROTECTION **MAY BE INCREASED AT LOWER WATTAGE FOR LOWER OUTPUT CURRENTS 1 COLL REF 47 MJE2955
VIN 5.2V
Measured Dropout Voltages
ILOAD 2A 1A 0.5A MTP50N05EL 47mV 22mV 11.5mV MTM25N05L 145mV 73mV 37mV
U
3 4
8 7
+
330F
LT1431 * TA07
FET Low Dropout 5V Regulator with Current Limit
12V MTP50N05EL MTM25N05L 0.002* 5V, 2.5A 2 3
+
47F
D G
S
+
4 47F
-
1.5V 7 LT1006
+
5
1N4148 1 COLL 3 4 V+ LT1431 RTOP GND-S 5 RMID GND-F 6 REF 8 7
6
LT1431 * TA08
*1.5" #23 SOLID COPPER WIRE ~0.002 3A LIMIT
7
LT1431
TYPICAL APPLICATIO S
12V to 5V Buck Converter with Foldback Current Limit*
PULSE ENGINEERING #PE-51515 VIN VIN VOUT LT1089 HI-SIDE SWITCH GND MBR735
80 VIN = 9V 70
LOGIC IN
EFFICIENCY (%)
5k
1500pF 2 COMP 1 COLL REF LT1431 RMID GND-F 6
3 4
V+ RTOP GND-S 5
8 7
30 0 1 2 3 4 ILOAD (A)
LT1431 * TA10
*CONTACT LTC FOR HIGH EFFICIENCY SWITCHING REGULATORS
Isolated 5V to 15V Flyback Converter
COILTRONICS CTX02-11934 4.5V TO 5.5V 0.47F 3k 6, 7 9 MUR105 -15V, 70mA C* 15k
MUR105
*
4, 5
*
2 10
+
50F
VIN LT1172 OR LT1072 GND
VOUT
VC 1
*
MUR105
1.5k 4N36 MEASURED EFFICIENCY LT117267.8% AT 2.2W OUT LT107268.6% AT 2.2W OUT LT107161.1% AT 4.4W OUT 0.68F 0.1F 2.4k 1 20k 2 3 V+ 8 REF LT1431 COMP GND-S 5 GND-F 6
LT1431 * TA11
8
+
U
Buck Converter Efficiency
100 0.5W
VIN = 12V
60 VIN = 15V 50
40
5
6
7
8
+
5V, 7A 3300F
LT1431 * TA09
Fully Loaded Output Ripple vs Filtering
C* LT1172 LT1072
+
210F 30mVP-P 40mVP-P
L*
+
100F
+
100F
6mVP-P
8mVP-P
*L BELL INDUSTRIES J.W. MILLER DIVISION 9310-36 10H, 450mA
LT1431 * TA12
+
C*
15V, 70mA
13.3k
COLL
2.7k
LT1431
TYPICAL APPLICATIO S
5V Power Supply Monitor with 500mV Window and 50mV Hysteresis
6
1k
6k* 1N4148
COLL REF LT1431 5k
COLL REF LT1431 5k
VOUT
V+
V+
GND-S
GND-F
GND-S
10**
VIN
1
+
C1 220F 35V
D1 BAT85 5 VIN LT1170 GND 3 VC FB 1 R2 1k C3 0.1F C4 0.033F D3 MBR330 2 VSW 4 C5 0.047F
R1 470k
+
C2 4.7F 35V TANTALUM
OFF
1
RUN = 0 SHUTDOWN > 3V
R3 10k
RTN
2 NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTANCES ARE IN , 0.25W, 5% 2. ALL CAPACITANCES ARE IN F, 50V, 10% 3. SHUTDOWN LOGIC STATE MUST BE DEFINED BY A LOGIC GATE OR BY TYING TO GND
U
Transfer Function
1k
4k* "HIGH" FOR OVER VOLTAGE OR UNDER VOLTAGE
5 4 3 2 1
GND-F 10** *DETERMINES WINDOW SIZE V = (R - 5)(0.5mA) **SETS HYSTERESIS
LT1431 * TA13
0
0
1
2
3 VIN
4
5
6
LT1431 * TA14
High Efficiency Buck Converter E = 85% to 89%
BOLD LINE INDICATES HIGH CURRENT PATHS * = 1% FILM RESISTORS C1 = NICHICON-UPL1V221MPH C6 = NICHICON-UPL1C471MPH6 D1, D2 = PHILIPS-BAT85 D3 = MOTORALA-MBR330 L1 = COILTRONICS CTX50-3-MP C3, C4, C5 = WIMA-MKS-2
D4 BAT85
L1 50H 3A
0.12m ESR
+
C6 470F 16V 5V 2.5A
D2 BAT85 Q2 2N3904 2 Q1 VN2222LL Q3 2N3904 3 COMP V+ 1 COLL REF RMID GND-F 6 8 7
R6* 23.7k
4 R4 100 R5 680 R8* 24.9k
VR2 LT1431CN8 RTOP GND-S 5
R7* 24.9k
LT1431 * TA15
9
LT1431
SCHE ATIC DIAGRA
Q5 R1 35k R2 35k 4X
Q7 3X
Q1
Q2
Q3
8 REF R6 8.5k Q4 RTOP 4 R3 5k R MID 7 Q8 10X R4 5k GND-SENSE 5 R5 5k R8 600 R7 2.5k
10
W
Q13 3 Q17 V + Q11 Q10 Q12 Q6 2X Q9 5X R11 11k C2 65pF R13 6.5k Q14 C1 22pF R12 1k R15 5k C4 1pF COMP 2 C3 6pF R17 1.5k COLLECTOR 1 Q20 2X Q22 45X R9 2.5k Q18 Q19 Q15 Q16 R16 11 R21 100k R14 11 R20 5k Q21 2.5X R10 340 R18 50k R19 3.6 6 GND-FORCE
LT1431 * SD01
W
LT1431
PACKAGE DESCRIPTIO
0.290 - 0.320 (7.366 - 8.128)
0.008 - 0.018 (0.203 - 0.460) 0.385 0.025 (9.779 0.635)
0.300 - 0.320 (7.620 - 8.128)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 +0.635 8.255 -0.381
)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights.
U
Dimensions in inches (millimeters) unless otherwise noted. J8 Package 8-Lead Ceramic DIP
0.405 (10.287) MAX 8 7 6 5
0.005 (0.127) MIN
0.025 (0.635) RAD TYP 1 0.055 (1.397) MAX 2 3
0.220 - 0.310 (5.588 - 7.874)
4
0.200 (5.080) MAX 0.015 - 0.060 (0.381 - 1.524)
0 - 15
0.038 - 0.068 (0.965 - 1.727) 0.014 - 0.026 (0.360 - 0.660)
0.125 3.175 0.100 0.010 MIN (2.540 0.254)
J8 0392
N8 Package 8-Lead Plastic DIP
0.400 (10.160) MAX 8 7 6 5
0.250 0.010 (6.350 0.254)
1
2
3
4 0.130 0.005 (3.302 0.127)
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.020 (0.508) MIN
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
N8 0392
11
LT1431
PACKAGE DESCRIPTIO U
Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic SOIC
0.189 - 0.197 (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157 (3.810 - 3.988)
1 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0.016 - 0.050 0.406 - 1.270
2
3
4
0.053 - 0.069 (1.346 - 1.752) 0.004 - 0.010 (0.101 - 0.254)
0- 8 TYP
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0392
Z Package 3-Lead TO-92
0.060 0.005 (1.524 0.127) DIA 0.180 0.005 (4.572 0.127) 0.90 (2.286) NOM
0.060 0.010 (1.524 0.254)
0.180 0.005 (4.572 0.127)
0.140 0.010 (3.556 0.127)
0.500 (12.79) MIN
0.050 (1.270) MAX UNCONTROLLED LEAD DIA 0.020 0.003 (0.508 0.076) 0.016 0.03 (0.406 0.076)
5 NOM
10 NOM
0.015 0.02 (0.381 0.051)
Z3 1191
0.050 0.005 (1.270 0.127)
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP1292 5K REV B
(c) LINEAR TECHNOLOGY CORPORATION 1992

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