Not Recommended For new Design
LX1570 / LX1571
P
HASE
M
ODULATED
AC S
YNCHRONOUS
-S
IDE
C
ONTROLLER
T
H E
I
N F I N I T E
P
O W E R
O F
I
N N O V A T I O N
P
R E L I M I N A R Y
D
A T A
S
H E E T
DESCRIPTION
The LX1570/71 series of controller ICs are only approach a certain maximum duty cycle,
designed to provide all control functions in a limited by the minimum delay and the magnetic
secondary-side regulator for isolated auxiliary or BH loop characteristic of the Mag Amp core.
secondary power supplies. Auxiliary or This forces an increase in the size of the main
secondary-side controllers are used in a variety transformer as well as the output inductor,
of applications including multiple output off-line resulting in higher overall system cost.
The
power supplies, commonly found in desktop
LX1570/71 eliminates all the disadvantages of
computers, as well as telecommunications
the Mag Amp approach as well as improving
applications. Although they can be used in all
system performance and reducing overall
secondary
output
applications
requiring
system cost.
The LX1570/71 is a current mode
precision regulation, they are mainly optimized controller IC that controls the duty cycle of a
for outputs delivering more than 3A current switch in series with the secondary AC output of
where standard three-terminal regulators lack the the power transformer in buck-derived
desired efficiency. For these applications, the applications, such as forward or bridge
Mag Amp regulators have traditionally been topologies. It offers features such as 100% duty
used. However, Mag Amps have several cycle operation for maximum energy transfer,
disadvantages. First, because they have to pulse-by-pulse and hiccup current limiting with
withstand the maximum input voltage during a long off-time between the cycles for reduced
short-circuit condition, they are "over designed", power dissipation, high-frequency operation for
typically by 2 times, increasing the cost and size smaller magnetics, soft start, and current mode
of the power supply. Second, Mag Amps are control for excellent dynamic response.
inherently leading edge modulators, so they can
IMPORTANT:
For the most current data, consult
MICROSEMI’s
website:
http://www.microsemi.com
KEY FEATURES
REPLACES COSTLY MAG-AMP
CORES WITH A LOW ON-
RESISTANCE MOSFET
LOOK-AHEAD SWITCHINGTM
ENSURES SWITCH TURN ON
BEFORE THE AC INPUT TO
ACHIEVE 100% ENERGY
TRANSFER
LOWER OVERALL SYSTEM
COST
LOWER PEAK CURRENT
STRESS ON THE PRIMARY
SWITCH
ALLOWS HIGHER OPERATING
FREQUENCY AND SMALLER
OUTPUT INDUCTOR
EASY SHORT-CIRCUIT
PROTECTION
CURRENT MODE APPROACH
ACHIEVES EXCELLENT
DYNAMIC RESPONSE
APPLICATIONS
SECONDARY-SIDE
REGULATOR IN OFF-LINE
POWER SUPPLIES
COMPUTER POWER
SUPPLIES, 3.3V OUTPUT FOR
NEW LOW-VOLTAGE
PROCESSORS AND
MEMORIES
TELECOMMUNICATION AND
MILITARY DC/DC
CONVERTERS
PRODUCT HIGHLIGHT
Aux Output
12V/8A
Available Options Per Part#
Part #
OUT
DRV
C.S.
V
FB
C.L.
Threshold
C.S.
Option
Resistive
Application
V
CC
LX1570
-0.2V
Sensing
Current
Trans-
former
LX1571
COMP
C
T
GND
S.S.
Output
Current
<4A
Output
Current
>4A
LX1571
1V
Sensing
T
A
(°C)
0 to 70
-40 to 85
-55 to 125
M
PACKAGE ORDER INFO
Plastic DIP
Plastic SOIC
DM
8-Pin
8-Pin
RoHS Compliant / Pb-free
Transition DC: 0440
Y
Ceramic DIP
8-Pin
-
-
LX157xMY
RoHS Compliant / Pb-free
Transition DC: 0503
LX157xCM
LX157xIM
-
LX157xCDM
LX157xIDM
-
Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1570CDM-TR).
Copyright
©
1997
Rev. 0.9.3b,2005-03-09
L
IN
F
INITY
M
ICROELECTRONICS
I
NC
.
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841, 714-898-8121, F
AX
: 714-893-2570
1
PRODUCT DATABOOK 1996/1997
LX1570/1571
P
HASE
M
ODULATED
AC S
YNCHRONOUS
S
ECONDARY
-S
IDE
C
ONTROLLER
P
R E L I M I N A R Y
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
S.S.
V
FB
COMP
C.S.
1
2
3
4
8
7
6
5
Supply Voltage (V
CC
) .................................................................................................... 40V
Digital Inputs ....................................................................................................... -0.3 to 7V
Output Peak Current Source (500nS) ........................................................................... 1A
Output Peak Current Sink (500nS) ................................................................................ 1A
Pb-free / RoHS Peak Package Solder Reflow Temp. (40 second max. exposure)............... 260°C (+0, -5)
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.
C
T
V
CC
OUT DRV
GND
M & Y PACKAGE
(Top View)
T H E R M A L D ATA
M PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
DM PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
Y PACKAGE:
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
θ
JA
130°C/W
165°C/W
95°C/W
S.S.
V
FB
COMP
C.S.
1
2
3
4
8
7
6
5
C
T
V
CC
OUT DRV
GND
DM PACKAGE
(Top View)
RoHS / Pb-free 100% Matte Tin Lean Finish
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.
LX1571 BLOCK DIAGRAM
2.5V
0.25V
Minimum
Current Comp
PWM Latch
R
S.S.
1
V
FB
2
COMP
3
C.S.
4
0.5V
Voltage Hiccup
Comp.
Voltage Mode Hiccup
5V
Internal
Bias
CHG
CONTROL
QUICK
CHG
CONTROL
Q
Error Amp
2R
1V
R
Current Mode
Hiccup Comp
C.S. Comp
S
6
OUT DRV
1.5V
2.5V
2.5V
REF
LATCH RESET
CONTROL
7
V
CC
C
T
8
Timing / Duty Cycle
Control
DISCH
CONTROL
VALLEY
THRESHOLD
CONTROL
LATCH
SET CONTROL
6V
16V
5
GND
Q
Q
R
S
Hiccup
Latch
2
Copyright © 1997
Rev. 0.9.3a
9/15/2004
PRODUCT DATABOOK 1996/1997
LX1570/1571
P
HASE
M
ODULATED
AC S
YNCHRONOUS
S
ECONDARY
-S
IDE
C
ONTROLLER
P
R E L I M I N A R Y
D
A T A
S
H E E T
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the ranges T
A
= -55 to 125ºC for the LX1570M/1571M, T
A
= -40 to 85ºC for the
LX1570I/1571I, and T
A
= 0 to 70ºC for LX1570C/1571C. V
CC
= 15V. Typ. number represents T
A
= 25ºC value.)
Parameter
Reference Section
Initial Accuracy
Line Regulation
Temp Stability
Symbol
Test Conditions
LX1570/1571
Min. Typ.
Max.
2.475
2.500
2.525
±1
±1.5
110
115
±1
Units
V
RI
∆V
RL
∆V
RT
f
O
∆f
OL
I
CHG
I
DISCH
I
LK
V
RPP
T
A
= 25ºC, measured at F.B pin
11V < V
CC
< 25
Note 2
C
T
= , T
J
= 25°C, measured at pin 6
Over Temp, measured at pin 6
V
%
%
kHz
kHz
%
mA
mA
µA
V
V
µΩ
µA
dB
µA
µA
V
V
V/µSec
ms/µF
mA
V
V
µA
µA
V/V
V/V
mV
mV
ns
V
V
V
V
V
Timing Section
Initial Accuracy
Line Voltage Stability
Charging Current
Discharging Current
Leakage Current
Ramp PK to PK
90
85
100
100
3
3.5
4
0.6
6
0.005
0.1
70
400
400
5.1
1
35
50
TBD
65
C.S.
INPUT
= 1.5V
C.S.
INPUT
= 0V
C.S.
INPUT
= 1.5V (1571), C.S.
INPUT
= -0.4V (1570)
Error Amp / Soft Start Comp Section
Transconductance
Input Bias Current
Open Loop Gain
Output Sink Current
Output Source Current
Output HI Voltage
Output LO Voltage
Slew Rate
g
m
I
B
A
VOL
I
EA(SINK)
I
EA(SOURCE)
V
COMP-HI
V
COMP-LO
S
K
SS
I
SS-DIS
LX1570
LX1571
LX1570
LX1571
LX1570
LX1571
LX1570
LX1571
LX1570
LX1571
LX1570
LX1571
V
CSI
-0.3
I
CSB
A
CS
V
CSMIN
10% Overdrive
V
CLP
V
CLH
V
HCCP
-0.18
0.9
-13.5
2.7
-15
3
-50
250
100
-0.2
1
-0.3
1.5
2
V
FB
= 2.6V
V
FB
= 2.4V
1
60
200
200
0.8
Soft-Start Section
Soft Start Timing Factor
Soft Start Discharge Current
Current Sense Section
Input Range
Input Current
C.S. Amplifier Gain
Minimum Current Threshold Voltage
C.S. Delay to Driver Output
C.L. Pulse-By-Pulse Threshold Voltage
C.L. Hiccup Threshold Voltage
Voltage Hiccup Threshold
-0.8
6
25
1
-16.5
3.3
200
-0.22
1.1
Note 2. Although this parameter is guaranteed, it is not 100% tested in production.
Copyright © 1997
Rev. 0.9.3a
9/15/2004
3
PRODUCT DATABOOK 1996/1997
LX1570/1571
P
HASE
M
ODULATED
AC S
YNCHRONOUS
S
ECONDARY
-S
IDE
C
ONTROLLER
P
R E L I M I N A R Y
D
A T A
S
H E E T
ELECTRICAL CHARACTERISTICS
Parameter
PWM Section
E.A. Output to PWM Drive Offset
Fixed Duty Cycle
V
OFS
D
t
R
/ t
F
V
DH
V
DL
V
DPD
V
ST
V
OFF
V
H
I
Qd
I
ST
Out Freq = 100kHz, C
L
= 0
C
L
= 1000pF
I
SOURCE
= 200mA, V
CS
= 0V, V
FB
= 2.3V
I
SINK
= 200mA, V
CS
= 1.2V, V
FB
= 2.3V
V
CC
= 0V, I
PULL UP
= 2mA
(Con't.)
Symbol
Test Conditions
LX1570/1571
Min. Typ.
Max.
1.7
52
2.0
54
50
13.5
0.8
1
15
9
5.5
16
10
6
18
150
17
11
6.5
30
250
2.4
56
Units
V
%
ns
V
V
V
V
V
V
mA
µA
Output Drive Section
Rise / Fall Time
Output HI
Output LO
Output Pull Down
UVLO Section
Start-Up Threshold
Turn Off Threshold
Hysterises
Supply Current Section
Dynamic Operating Current
Start-Up Current
FUNCTIONAL PIN DESCRIPTION
Pin
S.S.
#
1
Description
This pin acts as the soft-start pin. A capacitor connected from this pin to GND allows slow ramp up of the NI input
resulting in output soft start during start up. This pin is clamped to the internal voltage reference during the normal
operation and sets the reference for the feedback regulator.
This pin is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output
through a resistor divider to program the power supply voltage. This pin instead of the NI pin is internally trimed to
1% tolerance to include the offset voltage error of the error amp.
This pin is the Error Amplifier output and is made available for loop compensation. Typically a series R&C network
is connected from this pin to GND.
A voltage proportional to the inductor current is sensed by an external sense resistor (1570) or current transformer (1571)
in series with the return line and is connected to this pin. The output drive is terminated and latched off when this voltage
amplified by the internal gain (see option table) exceeds the voltage set by the E.A output voltage. The maximum
allowable voltage at this pin during normal operation is -0.8V typ for LX1570 and 6V typ for LX1571.
This pin is combined control circuitry and power GND. All other pins must be positive with respect to this pin, except
for C.S pin.
This pin drives a gate drive transformer which drives the power mosfet. A Schottky diode such as 1N5817 must be
connected from this pin to GND in order to prevent the substrate diode conduction.
This pin is the positive supply voltage for the control IC. A high frequency capacitor must be closely placed and
connected from this pin to GND to provide the turn-on and turn-off peak currents required for fast switching of the power
Mosfet.
The free running oscillator frequency is programmed by connecting a capacitor from this pin to GND.
V
FB
2
COMP
C.S.
3
4
GND
OUT
DRV
V
CC
5
6
7
C
T
8
4
Copyright © 1997
Rev. 0.9.3a
9/15/2004
PRODUCT DATABOOK 1996/1997
LX1570/1571
P
HASE
M
ODULATED
AC S
YNCHRONOUS
S
ECONDARY
-S
IDE
C
ONTROLLER
P
R E L I M I N A R Y
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
R2
300, 2W
C1
0.1µF, 50V
D1 1/2
MBR2545CT
L1
10µH (PE53700)
100kHz - 150kHz
AC(+)
D8
1N4937
Q1
IRLZ44
See Note 2
V
OUT (+)
20V-30V
20-30V, 100-150kHz
Secondary Transformer
T2
See Note 1
D1 2/2
MBR2545CT
C9
1500µF
C10
1500µF
C11
1500µF
C12
1500µF
3.3V / 7A
AC(-)
R5
0.02, 5W
C2
0.1µF
V
OUT (-)
D4
1N4148
V
IN
(17 to 20V)
R15
1M
R11
1.1k
U1
LX1570
1 S.S.
2 V
FB
R4
47
R6
324, 1%
C
T
8
V
CC
7
OUT DRV 6
GND 5
0.047µF
0.56µF
R7
1k, 1%
C6
3 COMP
4 C.S.
C5
1µF
C4
0.047µF
C7
C8
1000pF
R10
5k
1%
Note 1. T2 Core = RM4Z
Np = 25T #28AWG
Ns = 25T #28AWG
2. For further information on PE53700 and PE64978,
contact Pulse Engineering at (619) 674-8100.
FIGURE 1
— THE LX1570 IN A TYPICAL 3.3V / 7A SECONDARY-SIDE POWER SUPPLY APPLICATION
Copyright © 1997
Rev. 0.9.3a
9/15/2004
5
京公网安备 11010802033920号
EEWORLD
