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
45
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 IO±1A
Input Voltage (Analog Inputs pins 2,3) VI-0.3 to 5.5 V
Error Amp Output Sink Current ISINK(E.A) 10 mA
Power Dissipation (TA =25°C) PO1W
Storage Temperature Range Tstg -65 to 150 °C
Lead Temperature ( soldering 5 sec.) TL260 °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
TT
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, RT=10kΩ ,CT=3.3nF, TA=0 to 70° C, unless otherwise specified )
Characteristics Symbol Test Conditions Min Typ Max Unit
Reference Section
Reference Output Voltage VREF TJ =25°C, IREF=1mA 4.9 5.0 5.1 V
Line Regulation ∆VREF 12V≤VCC≤25V 6.0 20
Load Regulation ∆ VREF 1mA≤ IREF≤20mA 6.0 25 mV
Short Circuit Output
Current ISC TA=25°C100 180 mA
Oscillator Section
Oscillation Frequency f TJ=25°C47 52 57 KHz
Frequency change with
Voltage ∆f/∆Vcc 12V≤VCC≤25V 0.05 1.0 %
Oscillator Amplitude V(OSC) (Peak to Peak) 1.6 V
Error Amplitude Section
Input Bias Current IBIAS VFB=3V -0.1 -2 µA
Input Voltage VI(E,A) Vpin1=2.5V 2.5 2.58 V
Open Loop Voltage Gain AVOL 2V≤VO≤4V 65 90
Power Supply Rejection
ratio PSRR 12V≤VCC≤25V 60 70 dB
Output Sink Current ISINK Vpin2 =2.7V, Vpin1=1.1V 2 7 mA
Output Source current ISOURCE Vpin2=2.3V, Vpin1=5V -0.5 -1.0 mA
High Output Voltage VOH Vpin2=2.3V,RL=15kΩ to
GND 5.0 6.0
Low Output Voltage VOL Vpin2=2.7V,RL=15kΩ t o
PIN 8 0.8 1.1
V
Current Sense Section
Gain GV(Note 1& 2) 2.85 3.0 3.15 V/V
Maximum Input Signal VI(MAX) Vpin1 =5V(note 1) 0.9 1.0 1.1 V
Supply Voltage rejection SVR 12V≤Vcc≤25V(note 1) 70 dB
Input Bias Current IBIAS Vpin3= 3V -3.0 -10 µA
Output Section
Isink=20mA 0.08 0.4
Low Output Voltage VOL Isink=200mA 1.4 2.2
Isink=20mA 13 13.5
High Output Voltage VOH Isink=200mA 12 13.0
V
Rise Time tRTJ=25°C, CL =1nF(note
3) 45 150 nS
Fall time tFTJ=25°C, CL =1nF(note
3) 35 150 nS
Undervoltage Lockout Section
LND3842A,B/44A,B 14.5 16.0 17.5
Start Threshold VTH(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) VOPR(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 IST LND3842B/43B/44B/45B 0.45 1 mA
Operating Supply Current ICC(OPR) VPIN3=VPIN2 =0V 13 17 mA
Zener Voltage VZICC=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 VCC above the start threshold before setting it to 15V.
Note 1: Parameter measured at trip point of latch with Vpin2=0
Note 2: Gain defined as A=∆Vpin1/=∆Vpin3 : 0≤ Vpin3≤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
2V
FB
This is the inverting input of the Error Amplifier. It is normally connected to
the switching power supply output through a resistor divider.
3I
SENSE
A voltage proportional to inductor current is connected to this input. The
PWM uses this information to terminate the output switch conduction.
4R
T/CT
The oscillator frequency and maximum Output duty cycle are programmed
by connecting resistor RT to Vref and capacitor CT to ground.
5 GROUND This pin is the combined control circuitry and power ground
6OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to
1A are sourced and sinked by this pin.
7V
CC This pin is the positive supply of the integrated circuit.
8V
REF
This is the reference output. It provides charging current for capacitor CT
through resistor RT.
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
RC
S
CURRENT
SENSE
FB
V
COMP
GND
I
S
Peak current is determined by I
S max
y
1.0V
RS
Figure 3. Current Sense Circuit
LND3842
LND3844
16V 8.4V
10V 7.6V
V
V
ON
OFF
CC
V7
ON/OFF COMMAND
TO S/R OF IC
CC
CC
OFF ON
VVV
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 •
LND3842/43/44/45
LND3842
8
4
3
5
V
R
R
R
R
R
REF
T
T
S
SSLOPE
1
/ C
T
I
GND
I
SENSE
LND3842
8
4
3
5
V
R
R
R
R
R
REF
T
T
S
SSLOPE
1
/ C
T
I
GND
I
SENSE
Figure 4. Slope Compensation Techniques
+
BIAS
1mA
2R
+
-
ERROR
AMP
8
2
1
5
SCR must be selected for a holding current of less than 0.5 mA.
A simple two transistor circuit can be used in place of the SCR
as shown.
Figure 5. Latched Shutdown
R
R
R
• 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
+
+
2R
1mA
+
-
2
1
2.5V
ERROR
AMP
5
FB
f
f
i
d
V
R
R
R
C
From V
O
Error Amp compensation circuit f or stabilizing any current-mode topology except
f or boost and f ly back conv erters operating with continuous inductor current.
2
-
1mA
1
+
2R
2.5V
ERROR
AMP
5
FB
f
f
i
d
V
R
R
R
C
From V
O
COMP
COMP
R
C
p
p
Error Amp compensation circuit f or stabilizing current-mode and f ly back
topologies operating with continuous inductor current.
Figure 6. Error Amplifier Compensation
R
R
• 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
+
5
BIAS
2R
1mA
+
-
ERROR
AMP
8
2
1
OSC
.01
µ
F47
C
/ C
R
T
T
T
T
4
V
REF
EXTERNAL
SYNC INPUT
Figure 7. External Clock Synchronization
R
R
R
R
+
5
1
2R
-
1mA
2
ERROR
AMP
+
8
BIAS
OSC
4
+
-
+
-
5Vref
S
R
1M
C
Figure 8. Soft-Start Circuit
R
R
R
• 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
TYPICAL PERFORMANCE CHARACTERISTICS
40
50
60
70
80
90
123456 10 100 1K 10K 100K 1M
f (Hz)
-20
0
20
40
60
80
(dB)
V = 15V
V = 2V to 4V
R = 100K
T = 25 C
cc
O
L
A
o
Figure 4. Error Amp Open-Loop Gain vs. FrequencyFigure 3. Maximum Output Duty Cycle vs. Timing Resistor
10 20 30 50 100 200 300 500
f
OSC
(KHz)
1
2
5
10
20
50
R
T
(K )
Ω
10 20 30 50 100 200 300 500
f
OSC
(KHz)
1
2
5
10
20
50
%
C = 100pFC = 200pF
C = 500pF
C = 1nF
C = 2nF
C = 5nF
C = 10nF
TT
T
T
T
TT
V =15V
T =25 C
cc
A
o
V =15V
cc
T =25 C
A
o
C =100pF
C =200pF
C =500pF
C =1nF
C =2nF
C =5nF
C =10nF
T
T
T
T
T
T
T
Figure 1. Timing Resistor vs. Oscillator Frequency Figure 2. Output Dead-Time vs. Oscillator Frequency
• 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
50
60
70
80
90
100
025 50 75 100
T ( C)
A
o
I
(mA)
SC
Figure 6. Reference Short Circuit Current vs. Temperature
0.2
0.4
0.6
0.8
1.0
1 234567
Figure 5. Current Sense Input Threshold vs. Output
V (V)
O
T = 25 C
T = 125 C
A
A
o
o
V
(V)
TH
OSCILLATOR
PWM
5V REG
OUTPUT
6
7
8
4
5
I
D
GND
C
/ C
R
R
T
TT
T
REF
V
CLOCK
LARGE R / SMALL C
OUTPUT
/ C
R
TT
/ C
R
TT
OUTPUT
TT
SMALL R / Large C
TT
Figure 7. Oscillator and Output Waveforms
• Linear Dimensions, Inc. • 445 East Ohio Street, Chicago IL 60611 USA • tel 312.321.1810 • fax 312.321.1830 • www.lineardimensions.com •