DATA SHEET
LND3842A/43A/44A/45A
LND3842B/43B/44B/45B
Current Mode PWM Controller
GENERAL DESCRIPTION
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).
FEATURES
•
•
•
•
Low start-up and operating Current
High Current Totem Pole Output
Undervoltage Lockout with Hysterisis
Operating Frequency up to 500KHZ
PIN CONFIGURATION
COMP
V
I
FB
1
2
3
4
8
7
6
5
V
V
REF
CC
SENSE
T
OUT
GND
R /C
T
•
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
ABSOLUTE MAXIMUM RATINGS
Characteristic
Supply voltage (low impedance source)
Output Current
Input Voltage (Analog Inputs pins 2,3)
Error Amp Output Sink Current
Power Dissipation (T
A =
25°C)
Storage Temperature Range
Lead Temperature ( soldering 5 sec.)
Symbol
Vcc
I
O
V
I
I
SINK(E.A)
P
O
T
stg
T
L
Value
30
±1
-0.3 to 5.5
10
1
-65 to 150
260
Units
V
A
V
mA
W
°C
°C
BLOCK DIAGRAM
V
CC
UVLO
SET/
5V V
REF
RESET
7
8
V
REF
36V
GND
5
V
REF
LOGIC
INTERNAL
BIAS
1/2 V
REF
+
POWER V
REF
-
ERR
AMP
2R
C.S.
COMP
R
PWM
LATCH
7
2
V
FB
R
1V
OUT
1
COMP
S
6
3
4
CURRENT
SENSE
T
R
T
/ C
T
OSCILLATOR
5
POWER GND
•
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
ELECTRICAL CHARACTERISTICS
(*Vcc =15 V, R
T
=10kΩ ,C
T
=3.3nF, T
A
=0 to 70° C, unless otherwise specified )
Characteristics
Reference Section
Reference Output Voltage
Line Regulation
Load Regulation
Short Circuit Output
Current
Oscillator Section
Oscillation Frequency
Frequency change with
Voltage
Oscillator Amplitude
Error Amplitude Section
Input Bias Current
Input Voltage
Open Loop Voltage Gain
Power Supply Rejection
ratio
Output Sink Current
Output Source current
High Output Voltage
Low Output Voltage
Current Sense Section
Gain
Maximum Input Signal
Supply Voltage rejection
Input Bias Current
Output Section
Low Output Voltage
High Output Voltage
Rise Time
Fall time
Symbol
V
REF
∆V
REF
∆
V
REF
I
SC
f
∆f/∆V
cc
V
(OSC)
I
BIAS
V
I(E,A)
A
VOL
PSRR
I
SINK
I
SOURCE
V
OH
V
OL
G
V
V
I(MAX)
SVR
I
BIAS
V
OL
V
OH
t
R
t
F
V
TH(ST)
V
OPR(MIN)
D
(MAX)
D
(MAX)
I
ST
I
CC(OPR)
V
Z
LND3842A/43A/44A/45A
LND3842B/43B/44B/45B
V
PIN3
=V
PIN2
=0V
I
CC
=25mA
0.17
0.45
13
38
Test Conditions
T
J
=25°C, I
REF
=1mA
12V≤V
CC
≤25V
1mA≤ I
REF
≤20mA
T
A
=25°C
T
J
=25°C
12V≤V
CC
≤25V
(Peak to Peak)
V
FB
=3V
V
pin1
=2.5V
2V≤V
O
≤4V
12V≤V
CC
≤25V
V
pin2
=2.7V, Vpin1=1.1V
V
pin2
=2.3V, V
pin1
=5V
V
pin2
=2.3V,R
L
=15kΩ to
GND
V
pin2
=2.7V,R
L
=15kΩ t o
PIN 8
(Note 1& 2)
V
pin1
=5V(note 1)
12V≤V
cc
≤25V(note
1)
Vpin3= 3V
I
sink
=20mA
I
sink
=200mA
I
sink
=20mA
I
sink
=200mA
T
J
=25°C, C
L
=1nF(note
3)
T
J
=25°C, C
L
=1nF(note
3)
LND3842A,B/44A,B
LND3842A,B/45A,B
LND3842A,B/44A,B
LND3842A,B/45A,B
LND3842A,B/43A,B
LND3842A,B/45A,B
47
Min
4.9
Typ
5.0
6.0
6.0
100
52
0.05
1.6
-0.1
2.5
90
70
7
-1.0
6.0
V
0.8
2.85
0.9
3.0
1.0
70
-3.0
0.08
1.4
13.5
13.0
45
35
14.5
7.8
8.5
7.0
95
47
16.0
8.4
10
7.6
97
48
1.1
3.15
1.1
-10
0.4
2.2
V/V
V
dB
µA
-2
2.58
Max
5.1
20
25
180
57
1.0
Unit
V
mV
mA
KHz
%
V
µA
V
dB
mA
mA
65
60
2
-0.5
5.0
13
12
V
150
150
17.5
9.0
11.5
8.2
100
50
0
0.3
1
17
nS
nS
Undervoltage Lockout Section
Start Threshold
Min. Operating Voltage
(After Turn on)
PWM Section
Max. Duty Cycle
Min. Duty cycle
Total Standby Current
Start-Up current
Operating Supply Current
Zener Voltage
V
V
%
mA
mA
V
30
*Adjust V
CC
above the start threshold before setting it to 15V.
•
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
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.
PIN DESCRIPTION
No
1
2
3
4
5
6
7
8
FUNCTION
COMP
V
FB
I
SENSE
R
T
/C
T
GROUND
OUTPUT
V
CC
V
REF
DESCRIPTION
This pin is the Error Amplifier output and is made for loop compensation
This is the inverting input of the Error Amplifier. It is normally connected to
the switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The
PWM uses this information to terminate the output switch conduction.
The oscillator frequency and maximum Output duty cycle are programmed
by connecting resistor R
T
to V
ref
and capacitor C
T
to ground.
This pin is the combined control circuitry and power ground
This output directly drives the gate of a power MOSFET. Peak currents up to
1A are sourced and sinked by this pin.
This pin is the positive supply of the integrated circuit.
This is the reference output. It provides charging current for capacitor C
T
through resistor R
T
.
TYPICAL APPLICATIONS
2.5V
1mA
+
2
1
-
Figure 1. Error Amp Configuration
•
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
V
CC
7
ON/OFF COMMAND
TO S/R OF IC
I
CC
13mA
LND3842
LND3844
LND3843
LND3845
V
ON
V
OFF
16V
10V
8.4V
7.6V
.2mA
V
CC
V
ON
During UVLO, the Output is low
V
OFF
Figure 2. Undervoltage Lockout
+
ERROR
AMP
2R
R
1V
V
I
S
R
R
S
C
FB
2
1
3
-
COMP
CURRENT
SENSE
CURRENT
SENSE
COMPARATOR
5
GND
y
Peak current is determined by I
S max
1.0V
RS
Figure 3. Current Sense Circuit
•
Linear Dimensions, Inc.
•
445 East Ohio Street, Chicago IL 60611 USA
•
tel 312.321.1810
•
fax 312.321.1830
•
www.lineardimensions.com
•
