LIN D
O C
#:
1431
LX1431
P
ROGRAMMABLE
R
EFERENCE
T
H E
I
N F I N I T E
P
O W E R
O F
I
N N O VA T I O N
P
R O D U C T I O N
D
A T A
S
H E E T
DESCRIPTION
The LX1431 is an adjustable shunt voltage
regulator featuring 100mA sink capability, a
0.4% initial reference voltage tolerance and
a 0.3% typical temperature stability. This
product, which is ideal for use in Pentium
®
applications, is equipped with on-chip di-
vider resistors, enabling it to be configured
as a 5V shunt regulator. In this configura-
tion, the LX1431 has an initial voltage toler-
ance of
only
1% and requires no additional
exter nal components. The Linfinity
LX1431EB evaluation board and design kit
is available to assist engineers in quickly
configuring the most efficient, cost-effective
Pentium designs.
The output voltage of the LX1431 may be
set to any value between 2.5V and 36V
through the addition of two external resis-
tors, which is of particular importance in the
design of both adjustable and switching
power supplies. In addition, the nominal
internal current limit of 100mA may be de-
creased with the addition of a single exter-
nal resistor.
For applications requiring an adjustable
reference, the Linfinity LX6431CLP, a simpli-
fied three-pin programmable reference, may
be used. Because the LX6431 is pin-for-pin
compatible with Linfinity's earlier TL431, use
of this product provides designers a simple
migration path to the more robust LX6431.
A separate LX6431 data sheet is available
which details the specifics of this product.
In addition, Pentium designers may use
Linfinity's LX8585/8585A 4.6A or LX8584/
8584A 7A Low Dropout Regulators to achieve
the most optimum motherboard configura-
tion.
K E Y F E AT U R E S
p
GUARANTEED 0.4% INITIAL VOLTAGE
TOLERANCE
p
0.1Ω TYPICAL DYNAMIC OUTPUT
IMPEDANCE
p
FAST TURN-ON
p
SINK CURRENT CAPABILITY, 1mA TO 100mA
p
LOW REFERENCE PIN CURRENT
A P P L I C AT I O N S
s
s
s
s
LINEAR REGULATORS
ADJUSTABLE POWER SUPPLIES
SWITCHING POWER SUPPLIES
LX1431EB EVALUATION BOARD FOR
PENTIUM APPLICATIONS AVAILABLE.
CONSULT FACTORY.
PRODUCT HIGHLIGHT
T
HE
LX8584A
5V
3
AND
LX1431
V
OUT
2
IN
75
AND
166MH
Z
P54C P
R O C E S S O R
A
P P L I C ATIONS
U
S I N G
3.3V C
ACHE
V
O
7A
(See Table Below)
PLACE IN µP SOCKET CAVITY
V
IN
LX8584A
1kW
ADJ
1
250pF
2
220µF
10V
Low ESR
from
Sanyo
0.1µF
50V
3
V
+
1
COL
REF
8
2.84kW
0.1%
1kW
0.01µF
3x
330µF, 6.3V
Low ESR
Oscon Type
from Sanyo
100µF x 6
10V
AVX TYPE
TPS
1k
0.1%
µP
Load
LX1431
SGND
5
FGND
6
21k
1%
JP1
1µF x 10
SMD
V
O
3.50
3.38
JP1
Short
Open
TYPICAL APPLICATION
120/166MHz, VRE, 3.3V Cache
75/90/100/133MHz, STND, 3.3V Cache
Thick traces represent high current traces which
must be low resistance / low inductance traces in
order to achieve good transient response.
PA C K A G E O R D E R I N F O R M AT I O N
T
A
(°C)
0 to 70
-40 to 85
M
Plastic DIP
8-pin
LX1431CM
LX1431IM
DM
Plastic SOIC
8-pin
LX1431CDM
LX1431IDM
Note: All surface mount packages are available in Tape & Reel.
Append the letter "T" to part number (i.e. LX1431CDMT).
F O R F U R T H E R I N F O R M AT I O N C A L L ( 7 1 4 ) 8 9 8 - 8 1 2 1
Copyright © 1997
Rev. 1.2 4/97
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841
1
PRODUCT DATABOOK 1996/1997
LX1431
P
ROGRAMMABLE
R
EFERENCE
P
R O D U C T I O N
D
A T A
S
H E E T
A B S O L U T E M A X I M U M R AT I N G S
(Note 1)
PACKAGE PIN OUTS
V
+
, V
COLLECTOR
................................................................................................................. 36V
V
COMP
, R
TOP
, R
MID
, V
REF
...................................................................................................... 6V
GND-F to GND-S ........................................................................................................ 0.7V
Operating Junction Temperature
Plastic (M, DM Packages) ..................................................................................... 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature ..................................................................................................... 300°C
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect
to Ground. Currents are positive into, negative out of the specified terminal.
COLLECTOR
COMP
V
+
R
TOP
1
2
3
4
8
7
6
5
REF
R
MID
GND-F
GND-S
M PACKAGE
(Top View)
T H ER MAL DATA
M PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
DM PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
165°C/W
95°C/W
COLLECTOR
COMP
V
+
R
TOP
1
2
3
4
8
7
6
5
REF
R
MID
GND-F
GND-S
DM PACKAGE
(Top View)
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
θ
JA
).
The
θ
JA
numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
BLOC K DIAGRAM
R
TOP
4
5K
REF 8
7
V
+
3
COMP
2
COLLECTOR
1
gm=
60µA/V
R
MID
5K
2.5V
5
GND-SENSE
6
GND-FORCE
2
Copyright © 1997
Rev. 1.2 4/97
PRODUCT DATABOOK 1996/1997
LX1431
P
ROGRAMMABLE
R
EFERENCE
P
R O D U C T I O N
D
A T A
S
H E E T
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for LX1431C with 0°C
≤
T
A
≤
70°C, LX1431I with -40°C
≤
T
A
≤
85°C.)
Parameter
Reference Voltage
Reference Drift
Voltage Ratio, Reference to Cathode
(Open Loop Gain)
Reference Input Current
Minimum Operating Current
Off-State Cathode Current
Off-State Collector Leakage Current
Dynamic Impedance
Collector Current Limit
5V Reference Output
Symbol
V
REF
Test Conditions
LX1431I
LX1431C
Units
Min. Typ. Max. Min. Typ. Max.
2510 2490 2500 2510
mV
2535 2480
2520
mV
30
ppm/°C
1.0
0.2 1.0
mV/V
1
0.2
1
1.5
1.2
1
0.6
1
1
1
15
2
1
1
5
2
0.1
0.1
360 100
360
5050 4950 5000 5050
µA
µA
mA
µA
µA
µA
µA
Ω
mA
mV
V
KA
= 5V, I
K
= 2mA, T
A
= 25°C
2490 2500
V
KA
= 5V, I
K
= 2mA
2465
∆V
REF
/∆T V
KA
= 5V, I
K
= 2mA
50
0.2
∆V
REF
I
K
= 2mA, V
KA
= 3V to 36V
∆V
KA
0.2
V
KA
= 5V, T
A
= 25°C
[I
REF
]
V
KA
= 5V
0.6
V
KA
= V
REF
to 36V, T
A
= 25°C
I
MIN
V
KA
= 36V, V
REF
= 0V, T
A
= 25°C
[I
OFF
]
V
KA
= 36V, V
REF
= 0V
V
COLL
= 36V, V
+
= 5V, V
REF
= 2.4V, T
A
= 25°C
[I
LEAK
] V
+
COLL
= 36V, V = 5V, V
REF
= 2.4V
V
KA
= V
REF
, I
K
= 1mA to 100mA, f
≤
1kHz, T
A
= 25°C
[Z
KA
]
80
V
KA
= V
REF
+ 50mV
I
LIM
4950 5000
Internal Divider Used, I
K
= 2mA, T
A
= +25°C
Copyright © 1997
Rev. 1.2 4/97
3
PRODUCT DATABOOK 1996/1997
LX1431
P
ROGRAMMABLE
R
EFERENCE
P
R O D U C T I O N
D
A T A
S
H E E T
A P P L I C AT I O N I N F O R M AT I O N
PIN FUNCTIONS
Pin 1 COLL:
Open collector of the output transistor. The
maximum pin voltage is 36V. The saturation voltage at 100mA
is approximately 1V.
Pin 2 COMP:
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.
Pin 3 V
+
:
Bias voltage for the entire shunt regulator. The
maximum input voltage is 36V and the minimum to operate is
equal to V
REF
(2.5V). The quiescent current is typically 0.6mA.
Pin 4 R
TOP
:
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.
Pin 5 GND-S:
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).
Pin 6 GND-F:
Emitter of the output transistor and substrate
connection for the die.
Pin 7 R
MID
:
Middle of the on-chip resistive divider string
between R
TOP
and GND-S. The pin is tied to REF for self-
contained 5V operation. It may be left open if unused.
Pin 8 REF:
Control pin of the shunt regulator with a 2.5V
threshold.
COMP, R
TOP
, R
MID
, 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 LX1431 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).
FREQUENCY COMPENSATION
Excess capacitance on the REF pin can introduce enough
phase shift to induce oscillation when configured as a refer-
ence >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 LX1431 with dominant pole or 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.
4
Copyright © 1997
Rev. 1.2 4/97
PRODUCT DATABOOK 1996/1997
LX1431
P
ROGRAMMABLE
R
EFERENCE
P
R O D U C T I O N
D
A T A
S
H E E T
GRAPH / CURVE INDEX
Characteristic Curves
FIGURE #
1.
2.
3.
4.
5.
6.
7.
COLLECTOR V
SAT
vs. TEMPERATURE vs. CURRENT
COMPENSATION PIN VOLTAGE vs. TEMPERATURE vs. I
COLL
I
LIMIT
vs. TEMPERATURE WITH EXTERNAL RESISTOR
REFERENCE VOLTAGE and REFERENCE CURRENT vs. V+
REFERENCE VOLTAGE and REFERENCE CURRENT vs. V+
2.5V REFERENCE I
K
vs. V
KA
REFERENCE VOLTAGE and REFERENCE CURRENT vs. TEMPERATURE
Copyright © 1997
Rev. 1.2 4/97
5
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