Datasheet LND3845A, LND3844B, LND3844A, LND3843B, LND3843A Datasheet (Linear Dimensions)

LND3842A/43A/44A/45A

DATA SHEET

LND3842B/43B/44B/45B

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.

Current Mode PWM Controller

FEATURES

• Low start-up and operating Current

• High Current Totem Pole Output

• Undervoltage Lockout with Hysterisis

• Operating Frequency up to 500KHZ

PIN CONFIGURATION

The LND384XB has Start-Up current of .45mA(typ).
The LND384XA has Start-Up current of .17mA(typ).

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COMP

I

SENSE

R

T

V

/ C

FB

T

1

2

3

45

8

7

6

V

REF

V

CC

OUT

GND

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LND3842/43/44/45

ABSOLUTE MAXIMUM RATINGS

Characteristic Symbol Value Units

Supply voltage (low impedance source) Vcc 30 V

Output Current I

Input Voltage (Analog Inputs pins 2,3) V

Error Amp Output Sink Current I

Power Dissipation (T

A =

25°C)

Storage Temperature Range T

Lead Temperature ( soldering 5 sec.) T

BLOCK DIAGRAM

V

8

V

2

COMP

1

CURRENT
SENSE

3

4

REF

FB

R/ C

TT

INTERNAL
BIAS

1/2 V

REF

5V V

+

ERR
AMP

-

SET/

REF

RESET

OSCILLATOR

V

REF

LOGIC

2R

R

UVLO

1V

O

I

SINK(E.A)

P

O

stg

L

C.S.
COMP

±1

-0.3 to 5.5 V

10 mA

1W

-65 to 150

260

R

PWM
LATCH

S

T

A

°C

°C

36V

POWER V

V

CC

GND

REF

OUT

POWER GND

7

5

7

6

5

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LND3842/43/44/45

ELECTRICAL CHARACTERISTICS

(*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 V
Line Regulation
Load Regulation
Short Circuit Output

Current

∆V
∆ V

I

SC

REF

Oscillator Section

Oscillation Frequency f
Frequency change with
Voltage
Oscillator Amplitude V

∆f/∆V

(OSC)

Error Amplitude Section

Input Bias Current I
Input Voltage V
Open Loop Voltage Gain A
Power Supply Rejection
ratio
Output Sink Current I

Output Source current I

High Output Voltage V

Low Output Voltage V

BIAS

I(E,A)

VOL

PSRR

SINK

SOURCE

OH

OL

Current Sense Section

Gain G
Maximum Input Signal V

V

I(MAX)

Supply Voltage rejection SVR
Input Bias Current I

BIAS

Output Section

Low Output Voltage V

High Output Voltage V

Rise Time t

Fall time t

OL

OH

R

F

Undervoltage Lockout Section

Start Threshold V

Min. Operating Voltage
(After Turn on)

TH(ST)

V

OPR(MIN)

PWM Section

Max. Duty Cycle D

Min. Duty cycle D

(MAX)

(MAX)

Total Standby Current

Start-Up current I

Operating Supply Current I
Zener Voltage V

ST

CC(OPR)

Z

REF

REF

TJ =25°C, I
12V≤V
1mA≤ I

CC

REF

REF

≤25V

≤20mA

=1mA

TA=25°C

=25°C

T

J

cc

12V≤V

CC

≤25V

(Peak to Peak) 1.6 V

VFB=3V -0.1 -2
V

=2.5V 2.5 2.58 V

pin1

2V≤V

≤4V

O

12V≤V

V

V

V

≤25V

CC

=2.7V, Vpin1=1.1V 2 7 mA

pin2

=2.3V, V

pin2

=2.3V,RL=15kΩ to

pin2

=5V -0.5 -1.0 mA

pin1

GND
V

=2.7V,RL=15kΩ t o

pin2

PIN 8

(Note 1& 2) 2.85 3.0 3.15 V/V
V

=5V(note 1) 0.9 1.0 1.1 V

pin1

12V≤V

≤25V(note 1)

cc

Vpin3= 3V -3.0 -10

I

=20mA 0.08 0.4

sink

I

=200mA 1.4 2.2

sink

I

=20mA 13 13.5

sink

I

=200mA 12 13.0

sink

TJ=25°C, CL =1nF(note

3)
TJ=25°C, CL =1nF(note

3)

LND3842A,B/44A,B 14.5 16.0 17.5
LND3842A,B/45A,B 7.8 8.4 9.0
LND3842A,B/44A,B 8.5 10 11.5
LND3842A,B/45A,B 7.0 7.6 8.2

LND3842A,B/43A,B 95 97 100
LND3842A,B/45A,B 47 48 50

LND3842A/43A/44A/45A 0.17 0.3
LND3842B/43B/44B/45B 0.45 1
V

PIN3=VPIN2

=0V 13 17 mA

ICC=25mA 30 38 V

4.9 5.0 5.1 V

6.0 20

6.0 25

mV

100 180 mA

47 52 57 KHz

0.05 1.0 %

µA

65 90

60 70

dB

5.0 6.0
V

0.8 1.1

70 dB

µA

V

45 150 nS

35 150 nS

V

V

%

0

mA

*Adjust VCC above the start threshold before setting it to 15V.

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LND3842/43/44/45

Note 1: Parameter measured at trip point of latch with V
Note 2: Gain defined as A=∆V
Note 3: These parameters, although guaranteed, are not 100% tested in production.

pin1

/=∆V

pin3

: 0≤ V

pin3

pin2=0

≤0.8V.

PIN DESCRIPTION

No FUNCTION DESCRIPTION

1 COMP This pin is the Error Amplifier output and is made for loop compensation

2V

3I

4R

FB

SENSE

T/CT

5 GROUND This pin is the combined control circuitry and power ground

6OUTPUT

7V

8V

CC

REF

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

to V

T

and capacitor CT to ground.

ref

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
through resistor RT.

T

TYPICAL APPLICATIONS

2.5V

+

2

-

1

Figure 1. Error Amp Configuration

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1mA

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LND3842/43/44/45

13mA

I

CC

V

CC

7

ON/OFF COMMAND
TO S/R OF IC

LND3 842
LND3 844

V

V

ON

OFF

16V 8.4V

10V 7.6V

LND3 843
LND3 845

.2mA

V

V

OFF

V

ON

CC

During UVLO, the Output is low

Figure 2. Undervoltage Lockout

+

FB

2

-

1

3

5

V

I

S

R

C

R

S

COMP

CURRENT
SENSE

ERROR
AMP

2R

R

1V

CURRENT
SENSE
COMP ARATOR

GND

y

Peak current is determined by I

Figure 3. Current Sens e Circuit

S max

1.0V
R

S

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LND3842/43/44/45

V

REF

8

R

T

/ C

R

I

R

S

SLOPE

R

1

R

S

T

I

SENSE

T

LND3842

4

3

5

GND

Figure 4. Slope Compensation Techniques

8

R

2

R

+

-

I

S

R

ERROR
AMP

R

S

BIAS

SLOPE

R

1

+

1mA

V

REF

/ C

SENSE

T

2R

8

LND3842

4

3

R

5

GND

R

T

R

T

I

1

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

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LND3842/43/44/45

From V

From V

R

p

C

2.5V

O

+

R

i

V

FB

2

ERROR
AMP

+

1mA

-

R

d

R

C

f

f

1

COMP

Error Amp com pens ation circuit f or st abilizing any current -mode topology ex cept
f or boost and f ly back conv erters operat ing with cont inuous inductor current.

2.5V

O

+

+

1mA

ERROR

R

i

V

FB

2

AMP

-

p

R

d

R

C

f

f

1

2R

R

5

2R

R

COMP

Error Amp com pens ation circuit f or st abilizing c urrent -mode and f ly back
topologies operating with continuous inductor current.

Figure 6. Error Amplifier Compensation

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LND3842/43/44/45

R

47

8

R

T

4

2

R

+

-

OSC

ERROR
AMP

BIAS

+

1mA

2R

R

V

REF

R

/ C

T

T

EXTERNAL
SYN C INPUT

.01µF

C

T

1

5

Figure 7. External Clock Synchronization

8

R

R

BIAS

+

5Vref

-

4

+

OSC

+

1mA

ERROR

2

1M

C

1

AMP

-

Figure 8. Soft-Start Circuit

2R

+

R

S

R

-

5

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TYPICAL PERFORMANCE CHARACTERISTICS

R

T

(K )

Ω

50

20

C = 5nF

C = 10nF

T

10

T

C = 500pF

C = 2nF

T

T

C = 1nF

T

C = 100pFC = 200pF

T

T

LND3842/43/44/45

%

50

20

10

C =10nF

T

C =5nF

T

C =1nF

C =2nF

T

T

5

2

V =15V

cc

o

T =25 C

A

1

20 30 50 100 200 300 500

10

Figure 1. Timing Resistor vs. Oscillator Frequency

90

80

70

60

f

OSC

(KHz)

2

1

5

V =15V

cc

o

T =25 C

A

20 30 50 100 200 300 500

10

C =100pF

C =200pF

T

C =500pF

T

T

Figure 2. Out put Dead-Time vs. Os cill ator Frequency

(dB)

80

60

40

20

V = 15V

cc

V = 2V to 4V

O

R = 100K

L

T = 25 C

A

f

(KHz)

OSC

o

50

40

1

23

4

56

-20

0

100 1K 10K 100K 1M

10

Figure 4. Error Amp Open-Loop Gain vs. FrequencyFigure 3. Maximum Output Duty Cycle vs. Timing Resistor

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f (Hz)

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LND3842/43/44/45

V

TH

(V)

1.0

0.8

o

T = 125 C

A

0.6

0.4

0.2

1 234567

o

T = 25 C

A

Figure 5. Current Sens e Input Threshol d vs. Output

7

5V REG

R

R

/ C

TT

C

T

V

REF

8

T

4

PWM

CLOCK

OSCILLATOR

I

D

V (V)

O

I

SC

(mA)

100

90

80

70

60

50

25

0

50 75 100

T ( C)

A

Figure 6. Reference Short Circuit Current vs. Temperature

R

/ C

TT

OUTPUT

6

OUTPUT

LARGE R / SMALL C

R

/ C

TT

T

T

OUTPUT

o

5

SMALL R / Large C

GND

Figure 7. Oscillator and Output Waveforms

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T

T

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