Linear Dimensions LND3842B Current mode pwm controller Datasheet

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
FB
I
SENSE
R /C
T
T
1
8
V
2
7
V
3
6
OUT
4
5
GND
REF
CC
• 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
Symbol
Value
Units
Vcc
30
V
Output Current
IO
±1
A
Input Voltage (Analog Inputs pins 2,3)
VI
-0.3 to 5.5
V
ISINK(E.A)
10
mA
Power Dissipation (TA =25°C)
PO
1
W
Storage Temperature Range
Tstg
-65 to 150
°C
Lead Temperature ( soldering 5 sec.)
TL
260
°C
Supply voltage (low impedance source)
Error Amp Output Sink Current
BLOCK DIAGRAM
VCC
8
UVLO
VREF
7
36V
5V VREF SET/
RESET
GND
5
VREF LOGIC
INTERNAL
BIAS
1/2 VREF
POWER VREF
+
2
VFB
-
2R
ERR
AMP
C.S.
COMP
R
PWM
LATCH
1V
1
3
4
7
R
OUT
6
COMP
S
5
CURRENT
SENSE
POWER GND
T
R T / CT
OSCILLATOR
• 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, RT=10kΩ ,CT=3.3nF, TA=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
Symbol
Test Conditions
Min
Typ
Max
Unit
VREF
∆VREF
∆ VREF
TJ =25°C, IREF=1mA
12V≤VCC≤25V
1mA≤ IREF≤20mA
4.9
5.0
6.0
6.0
5.1
20
25
V
ISC
TA=25°C
100
180
mA
f
TJ=25°C
47
mV
52
57
KHz
1.0
%
∆f/∆Vcc
12V≤VCC≤25V
0.05
V(OSC)
(Peak to Peak)
1.6
IBIAS
VI(E,A)
AVOL
VFB=3V
Vpin1=2.5V
2V≤VO≤4V
65
-0.1
2.5
90
PSRR
12V≤VCC≤25V
60
70
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
5.0
6.0
Low Output Voltage
VOL
Current Sense Section
Gain
Maximum Input Signal
Supply Voltage rejection
Input Bias Current
Output Section
GV
VI(MAX)
SVR
IBIAS
Low Output Voltage
VOL
High Output Voltage
VOH
Rise Time
tR
Fall time
tF
Vpin2=2.3V,RL=15kΩ to
GND
Vpin2=2.7V,RL=15kΩ t o
PIN 8
(Note 1& 2)
Vpin1 =5V(note 1)
12V≤Vcc≤25V(note 1)
Vpin3= 3V
Isink=20mA
Isink=200mA
Isink=20mA
Isink=200mA
TJ=25°C, CL =1nF(note
3)
TJ=25°C, CL =1nF(note
3)
V
-2
2.58
µA
V
dB
V
2.85
0.9
13
12
0.8
1.1
3.0
1.0
70
-3.0
3.15
1.1
0.08
1.4
13.5
13.0
0.4
2.2
45
150
nS
35
150
nS
-10
V/V
V
dB
µA
V
Undervoltage Lockout Section
Start Threshold
Min. Operating Voltage
(After Turn on)
PWM Section
VTH(ST)
VOPR(MIN)
Max. Duty Cycle
D(MAX)
Min. Duty cycle
Total Standby Current
D(MAX)
Start-Up current
IST
Operating Supply Current
Zener Voltage
ICC(OPR)
VZ
LND3842A,B/44A,B
LND3842A,B/45A,B
LND3842A,B/44A,B
LND3842A,B/45A,B
14.5
7.8
8.5
7.0
16.0
8.4
10
7.6
17.5
9.0
11.5
8.2
LND3842A,B/43A,B
LND3842A,B/45A,B
95
47
97
48
100
50
0
0.3
1
17
30
0.17
0.45
13
38
LND3842A/43A/44A/45A
LND3842B/43B/44B/45B
VPIN3=VPIN2 =0V
ICC=25mA
V
V
%
mA
mA
V
*Adjust VCC 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 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.
PIN DESCRIPTION
No
FUNCTION
DESCRIPTION
1
COMP
This pin is the Error Amplifier output and is made for loop compensation
2
VFB
This is the inverting input of the Error Amplifier. It is normally connected to
the switching power supply output through a resistor divider.
3
ISENSE
A voltage proportional to inductor current is connected to this input. The
PWM uses this information to terminate the output switch conduction.
4
RT/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
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
VCC
This pin is the positive supply of the integrated circuit.
8
VREF
This is the reference output. It provides charging current for capacitor CT
through resistor RT.
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
VCC
ICC
7
ON/OFF COMMAND
TO S/R OF IC
LND3842
LND3844
LND3843
LND3845
VON
16V
8.4V
VOFF
10V
7.6V
13mA
.2mA
V CC
VON
During UVLO, the Output is low
VOFF
Figure 2. Undervoltage Lockout
+
V
IS
FB
COMP
R
RS
C
2
ERROR
AMP
2R
R
-
1V
1
CURRENT
SENSE
COMPARATOR
3
CURRENT
SENSE
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 •
LND3842/43/44/45
VREF
RT
IS
RSLOPE
R1
RS
RT / CT
ISENSE
VREF
8
RT
LND3842
4
IS
RT / CT
RSLOPE
R1
3
5
ISENSE
8
LND3842
4
3
5
RS
GND
GND
Figure 4. Slope Compensation Techniques
8
R
BIAS
R
+
1mA
+
2
ERROR
AMP
2R
-
R
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
• 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
+
2.5V
From VO
Ri
Rd Cf
1mA
+
VFB
2
Rf
1
2R
ERROR
AMP
-
R
COMP
5
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.
+
2.5V
1mA
From VO
Rp
+
Ri
Cp
Rd Cf
VFB
2
Rf
1
ERROR
AMP
-
COMP
2R
R
5
Error Amp compensation circuit f or stabilizing current-mode and f ly back
topologies operating with continuous inductor current.
Figure 6. Error Amplifier Compensation
• 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
8
VREF
R
BIAS
R
RT
4
RT / CT
EXTERNAL
SYNC INPUT
.01µF
OSC
+
1mA
+
CT
2
47
2R
ERROR
AMP
-
R
1
5
Figure 7. External Clock Synchronization
8
5Vref
+
R
BIAS
R
-
4
OSC
+
1mA
+
2
1M
ERROR
AMP
-
2R
+
R
S
R
-
1
C
5
Figure 8. Soft-Start Circuit
• 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
RT
(K Ω )
%
C = 200pF CT = 100pF
T
50
50
CT =1nF
C = 500pF
T
CT =2nF
CT = 1nF
CT =5nF
20
20
CT =10nF
CT = 5nF
C = 10nF
T
CT = 2nF
10
10
5
5
CT =500pF
CT =200pF
2
2
Vcc =15V
Vcc =15V
o
TA =25 C
o
TA =25 C
1
CT =100pF
1
10
20
30
50
100
200
300
500
10
f OSC (KHz)
20
30
50
100
200
300
500
f OSC (KHz)
Figure 2. Output Dead-Time vs. Oscillator Frequency
Figure 1. Timing Resistor vs. Oscillator Frequency
(dB)
90
80
80
60
Vcc = 15V
VO = 2V to 4V
RL = 100K
TA = 25 o C
70
40
60
20
50
0
40
-20
1
2
3
4
5
6
Figure 3. Maximum Output Duty Cycle vs. Timing Resistor
10
100
1K
10K
100K
1M
f (Hz)
Figure 4. Error Amp Open-Loop Gain vs. 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
ISC
(mA)
VTH
(V)
1.0
100
0.8
90
TA = 125o C
80
0.6
70
0.4
TA = 25o C
0.2
60
50
1
2
3
4
5
6
7
Figure 5. Current Sense Input Threshold vs. Output
VREF
PWM
CT
4
25
50
75
100
TA ( o C)
Figure 6. Reference Short Circuit Current vs. Temperature
5V REG
RT / CT
6
CLOCK
RT / CT
0
7
8
RT
VO (V)
OSCILLATOR
ID
OUTPUT
OUTPUT
LARGE R T / SMALL CT
RT / C T
OUTPUT
SMALL RT / Large CT
5
GND
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 •
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