LND3842A/43A/44A/45A
LND3842B/43B/44B/45B
DATA SHEET
GENERAL DESCRIPTION
Low start-up and operating Current
High Current Totem Pole Output
Undervoltage Lockout with Hysterisis
Operating Frequency up to 500KHZ
FEATURES
The LND3842B/43B/44B/45B and LND3842A
/43A/44A/45A are fixed frequency current mode
PWM controllers. They are specially designed for
OFF-line and DC to DC converter applications with
a minimal of external components. Internally
implemented circuits include a trimmed oscillator for
precise duty cycle control, a temperature
compensated reference, high gain error amplifier,
current sensing comparator. Protection circuitry
includes undervoltage lockout and current limiting.
The LND3843B, A and LND3844B, A have UVLO
thresholds of 16V(on) and 10 V (off). The
corresponding thresholds for the LND3843B, A/
45B,A are 8.4 V (on) and 7.6(off). The LND3842B,
A and LND3843B, A can operate within 100% duty
cycle. The LND3844B, A and LND3845B, A can
operate within 50% duty cycle.
The LND384XB has Start-Up current of .45mA(typ).
The LND384XA has Start-Up current of .17mA(typ).
PIN CONFIGURATION
3
4
5
6
7
8
COMP
V
GND
OUT
FB
I
SENSE
R
T
/ C
T
V
REF
V
CC
1
2
Current Mode PWM Controller
Linear Dimensions, Inc. 445 East Ohio Street, Chicago IL 60611 USA tel 312.321.1810 fax 312.321.1830
www.lineardimensions.com
Characteristic
Symbol
Value
Units
Supply voltage (low impedance source)
Vcc
30
V
Output Current
I
O
1
A
Input Voltage (Analog Inputs pins 2,3)
V
I
-0.3 to 5.5
V
Error Amp Output Sink Current
I
SINK(E.A)
10
mA
Power Dissipation (T
A =
25
C)
P
O
1
W
Storage Temperature Range
T
stg
-65 to 150
C
Lead Temperature ( soldering 5 sec.)
T
L
260
C
ABSOLUTE MAXIMUM RATINGS
LND3842/43/44/45
BLOCK DIAGRAM
C.S.
COMP
ERR
AMP
PWM
LATCH
R
S
T
+
-
OSCILLATOR
INTERNAL
BIAS
REF
SET/
RESET
V
REF
LOGIC
8
2
1
3
4
5
6
7
5
7
5V V
REF
FB
T
T
REF
CC
V
GND
POWER V
OUT
POWER GND
V
V
R / C
CURRENT
SENSE
COMP
1/2 V
REF
UVLO
1V
R
2R
36V
Linear Dimensions, Inc. 445 East Ohio Street, Chicago IL 60611 USA tel 312.321.1810 fax 312.321.1830
www.lineardimensions.com
(*Vcc =15 V, R
T
=10k
,C
T
=3.3nF, T
A
=0 to 70
C, unless otherwise specified )
Characteristics
Symbol
Test Conditions
Min
Typ
Max
Unit
Reference Section
Reference Output Voltage
V
REF
T
J
=25
C, I
REF
=1mA
4.9
5.0
5.1
V
Line Regulation
V
REF
12V
V
CC
25V
6.0
20
Load Regulation
V
REF
1mA
I
REF
20mA
6.0
25
mV
Short Circuit Output
Current
I
SC
T
A
=25
C
100
180
mA
Oscillator Section
Oscillation Frequency
f
T
J
=25
C
47
52
57
KHz
Frequency change with
Voltage
f/V
cc
12V
V
CC
25V
0.05
1.0
%
Oscillator Amplitude
V
(OSC)
(Peak to Peak)
1.6
V
Error Amplitude Section
Input Bias Current
I
BIAS
V
FB
=3V
-0.1
-2
A
Input Voltage
V
I(E,A)
V
pin1
=2.5V
2.5
2.58
V
Open Loop Voltage Gain
A
VOL
2V
V
O
4V
65
90
Power Supply Rejection
ratio
PSRR
12V
V
CC
25V
60
70
dB
Output Sink Current
I
SINK
V
pin2
=2.7V, Vpin1=1.1V
2
7
mA
Output Source current
I
SOURCE
V
pin2
=2.3V, V
pin1
=5V
-0.5
-1.0
mA
High Output Voltage
V
OH
V
pin2
=2.3V,R
L
=15k
to
GND
5.0
6.0
Low Output Voltage
V
OL
V
pin2
=2.7V,R
L
=15k
t o
PIN 8
0.8
1.1
V
Current Sense Section
Gain
G
V
(Note 1& 2)
2.85
3.0
3.15
V/V
Maximum Input Signal
V
I(MAX)
V
pin1
=5V(note 1)
0.9
1.0
1.1
V
Supply Voltage rejection
SVR
12V
V
cc
25V(note 1)
70
dB
Input Bias Current
I
BIAS
Vpin3= 3V
-3.0
-10
A
Output Section
I
sink
=20mA
0.08
0.4
Low Output Voltage
V
OL
I
sink
=200mA
1.4
2.2
I
sink
=20mA
13
13.5
High Output Voltage
V
OH
I
sink
=200mA
12
13.0
V
Rise Time
t
R
T
J
=25
C, C
L
=1nF(note
3)
45
150
nS
Fall time
t
F
T
J
=25
C, C
L
=1nF(note
3)
35
150
nS
Undervoltage Lockout Section
LND3842A,B/44A,B
14.5
16.0
17.5
Start Threshold
V
TH(ST)
LND3842A,B/45A,B
7.8
8.4
9.0
V
LND3842A,B/44A,B
8.5
10
11.5
Min. Operating Voltage
(After Turn on)
V
OPR(MIN)
LND3842A,B/45A,B
7.0
7.6
8.2
V
PWM Section
LND3842A,B/43A,B
95
97
100
Max. Duty Cycle
D
(MAX)
LND3842A,B/45A,B
47
48
50
%
Min. Duty cycle
D
(MAX)
0
Total Standby Current
LND3842A/43A/44A/45A
0.17
0.3
Start-Up current
I
ST
LND3842B/43B/44B/45B
0.45
1
mA
Operating Supply Current
I
CC(OPR)
V
PIN3
=V
PIN2
=0V
13
17
mA
Zener Voltage
V
Z
I
CC
=25mA
30
38
V
ELECTRICAL CHARACTERISTICS
LND3842/43/44/45
Linear Dimensions, Inc. 445 East Ohio Street, Chicago IL 60611 USA tel 312.321.1810 fax 312.321.1830
www.lineardimensions.com
*Adjust V
CC
above the start threshold before setting it to 15V.
Note 1: Parameter measured at trip point of latch with V
pin2=0
Note 2: Gain defined as A=
V
pin1
/=
V
pin3
: 0
V
pin3
0.8V.
Note 3: These parameters, although guaranteed, are not 100% tested in production.
No
FUNCTION
DESCRIPTION
1
COMP
This pin is the Error Amplifier output and is made for loop compensation
2
V
FB
This is the inverting input of the Error Amplifier. It is normally connected to
the switching power supply output through a resistor divider.
3
I
SENSE
A voltage proportional to inductor current is connected to this input. The
PWM uses this information to terminate the output switch conduction.
4
R
T
/C
T
The oscillator frequency and maximum Output duty cycle are programmed
by connecting resistor R
T
to V
ref
and capacitor C
T
to ground.
5
GROUND
This pin is the combined control circuitry and power ground
6
OUTPUT
This output directly drives the gate of a power MOSFET. Peak currents up to
1A are sourced and sinked by this pin.
7
V
CC
This pin is the positive supply of the integrated circuit.
8
V
REF
This is the reference output. It provides charging current for capacitor C
T
through resistor R
T
.
LND3842/43/44/45
PIN DESCRIPTION
TYPICAL APPLICATIONS
2.5V
1
2
+
-
Figure 1. Error Amp Configuration
1mA
Linear Dimensions, Inc. 445 East Ohio Street, Chicago IL 60611 USA tel 312.321.1810 fax 312.321.1830
www.lineardimensions.com
LND3842/43/44/45
+
-
ERROR
AMP
CURRENT
SENSE
COMPARATOR
R
2R
1V
2
1
3
5
R
R
C
S
CURRENT
SENSE
FB
V
COMP
GND
I
S
Peak current is determined by I
S max
y
1.0V
R S
Figure 3. Current Sense Circuit
LND3842
LND3844
16V
8.4V
10V
7.6V
V
V
ON
OFF
CC
V
7
ON/OFF COMMAND
TO S/R OF IC
CC
CC
OFF
ON
V
V
V
I
13mA
.2mA
During UVLO, the Output is low
Figure 2. Undervoltage Lockout
LND3843
LND3845
Linear Dimensions, Inc. 445 East Ohio Street, Chicago IL 60611 USA tel 312.321.1810 fax 312.321.1830
www.lineardimensions.com
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