KSI-L006-000
1
S3842P
Current Mode PWM Controller
Descriptions
The S3842, high performance current mode controller, Provides the necessary features to
off-line and DC-DC fixed frequency current control applications offering the designer a cost
effective solution with minimal external components. Internally protection circuity includes
built-in input and reference under-voltage lockout and current limiting with hysteresis.
Also other characteristics of internal circuit provide improved line regulation, enhanced load
response, trimmed oscillation for precise duty cycle control, a temperature compensated
reference, high gain error amplifier, current sensing comparator and totempole output
designed to source and sink high peak current from a capacitive load such as the gate of a
power MOSFET.
Features
Optimized for off-line control Current mode operation to 500
Low start up and operating current Under voltage lockout with 6V hysteresis
Pulse by pulse current limiting
Internally trimmed bandgap reference about 5V
Enhanced load response characteristic Automatic feed forward compensation
Ordering
Information
Type NO. Marking Package Code
S3842P S3842P DIP-8
Outline Dimensions unit :
mm
S
S
e
e
m
m
i
i
c
c
o
o
n
n
d
d
u
u
c
c
t
t
o
o
r
r
PIN Connections
1. Output / Compensation
2. Voltage feedback. Input
3. Current sense Input
4. Rt/Ct
5. GND
6. Output
7. Vcc
8. Vref
KSI-L006-000
2
S3842P
Absolute Maximum Ratings
Ta=25
C
Characteristic Symbol
Ratings
Unit
Supply voltage
V
cc
30 V
Current Sense and V
fb
Input
V
IN
-0.3 to V
cc
V
Total Power Supply and Zener Current
I
CC
+ I
Z
30 mA
Output Sink of Source Current
I
o
1 A
Error AMP Output Sink Current
I
eo
10
mA
Operating Ambient Temperature
T
a
0 to 70
C
Storage Temperature Range
T
stg
-65 to 150
C
Power Dissipation at T
a
50C
P
d
1 W
note) All voltages are with respect to PIN5, and current are positive into the specified pin.
PIN Description
PIN NO
Function
Description
1
Compensation Error amplifier output and is made available for loop compensation.
2
Voltage
feedback
Inverting input of error amplifier, normally connected to the switching
power supply output through a resistor driver.
3 Current
sense
A voltage proportional to inductor current is connected to this input.
The PWM uses this information to terminate the output.
4 R
t
/C
t
The oscillator frequency and maximum output duty cycle are
programmed by connecting resistor R
t
to Vref 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 current
up to 1.0A are sourced and sinked by this pin.
7 V
CC
This pin is the positive supply of the control IC.
8 Vref
This is the reference output. it provides charging current for capacitor
C
t
through resistor R
t
.
Block Diagram
KSI-L006-000
3
S3842P
Electrical Characteristics
(Unless otherwise stated, these specifications apply for 0
Ta
70
C;
V
CC
=15V
(Note.4),
R
L
=10 , C
L
=3.3nF
)
Characteristic Symbol
Test
Condition Min.
Typ.
Max.
Unit
1. Reference Section
Output Voltage
Vref
Ta
=25
C,
I
O
=1mA
4.90 5.00 5.10
V
Line Regulation
Vref
12V V
CC
25V
- 6 20 mV
Load Regulation
Vref
1mA I
O
20mA
- 6 25 mV
Temperature Stability
V
T
/V
T
(Note 1)
-
0.2
0.4
mV/
C
Output Noise Voltage
V
n
10Hz f 10KHz,T
a
=25
C(Note
1)
- 50 - uV
Long Term Stability
S
T
a
=125
C, 1000Hrs (Note 1)
- 5 - mV
Output Short Circuit
I
SC
-
-30
-100
-180 mA
2. Oscillator Section
Initial Accuracy
f
SC
T
a
=25
C
47 52 57 KHz
Voltage Stability
f /V
12 V
a
25V
- 0.05 1.0 %
Temperature Stability
f /T
T
min
T
a
T
max
(Note 1)
- 5 - %
Amplitude V
4
V
PIN4
Peak to Peak
-
1.7
-
V
3. Error Amp Section
Input Voltage
V
2
V
PIN1
=2.5V
2.42 2.50 2.58
V
Input Bias Current
I
b
-
- -0.3
-2.0
Open Loop Voltage Gain
A
VO1
2V V
O
4V
65 90 -
Supply Voltage Rejection
SVR
12V V
a
25V
60 70 -
Output Sink Current
I
O
V
PIN2
=2.7V, V
PIN1
=1.1V 2
6
-
mA
Output Source Current
I
O
V
PIN2
=2.3V, V
PIN1
=5V -0.5
-0.8
-
mA
V
OUT
High V
ch
V
PIN2
=2.3V, R
L
=15 to Ground
5 6 - V
V
OUT
Low V
c1
V
PIN2
=2.7V, R
L
=15 Pin8
- 0.7 1.1 V
4. Current Sense Section
Gain G
V
(Note 2 & 3)
2.8
3.0
3.2
V/V
Maximum Input Signal
V
3
V
PIN 1
=5V (Note 2)
0.9
1.0
1.1
V
Supply Volt Rejection
SVR
12 V
a
25V (Note 2)
- 70 -
Input Bias Current
I
b
-
- -2
-10
5.Output Section
I
SINK
=20mA -
0.1
0.4
V
Output Low Level
V
Ol
I
SINK
=200mA -
1.5
2.2
V
I
SOURCE
=20mA 13.0
13.5
-
V
Output High Level
V
Oh
I
SOURCE
=200mA 12.0
13.5
-
V
Rise time
t
r
T
a
=25
C, C
l
=1nF (Note 1)
- 50
150 ns
Fall time
t
f
T
a
=25
C, C
l
=1nF (Note 1)
- 50
150 ns
KSI-L006-000
4
S3842P
Electrical Characteristics(continued)
Characteristic Symbol
Test
Condition Min.
Typ.
Max.
Unit
6. Under-Voltage Lockout Section
Start Threshold
V
th
V
PIN7
where
V
PIN8
4.9V
14.5 16.0 17.5
V
Min. Operation Voltage
After Turn-On
V
CC(min)
V
PIN7
where
V
PIN8
1V
8.5 10.0 11.5 V
7. PWM Section
Maximum Duty Cycle
DC
max
-
93 97 100 ns
8. Total Standby Section
Start-Up Current
I
st
V
CC
= 15V before turn on
-
0.4
0.7
mA
Operating Supply Current
I
CC
V
PIN2
=
V
PIN3
= 0V
- 11 20 mA
Zener Voltage
V
Z
I
CC
=
25mA
- 36 - V
NOTE: 1.Thes parameters, although guaranteed.are not 100% tested in production
2.Parameter measured at trip piont of latch with V
pin2
=0
3.Gain defined as : A =V
PIN1
/V
PIN3
; 0 V
PIN3
0.8V
4.Adjust V
CC
above the start threshold before setting at 15V
Information in Using IC
1. Under voltage Lockout
To prevent erratic output behavior which activating
the power switch with extraneous leakage currents,
during under voltage lockout. Output(pin6) should be
shunted to ground with a bleeder resister.
The Vcc comparator upper and lower threshold are
16V/10V. The large hysteresis and low start up
currents makes it ideally suited in off-line converter
application where efficient bootstrap start-up
techniques are required.
O N /O F F C O M M A N D
T O R E S E T O F I C
V c c
V o n - 1 6 V
V o f f - 1 0 V
7
V cc
Icc
<17mA
<1mA
10V
16V
KSI-L006-000
5
2. Oscillator Waveforms and Maximum Duty Cycle
The oscillator frequency is programmed by the values
selected for the timing components Rt and Ct. Ct is
charged from 5V, Vref, through resistor Rt
to
approximately 2.8V and discharged to 1.2V by an
internal current sink.
During the discharge of Ct, the oscillator generates an
internal blanking pulse and the center input NOR gate high.
This makes output to be in a low state and control the
amount of output dead time.
3. Error AMP Configuration
Error amp output(Pin1) is provided for external loop
Compensation and error amp can source or sink up to 0.5mA.
The non-inverting input is internally biased at 2.5V and is
not pinned out. The converter output voltage is typically
divided down and monitored by the inverting input(pin2).
4. Current Sense Circuit
A normal operating conditions occurs when the power supply output is overloaded or if output voltage to 1.0V
Therefore the maximum peak switch current is lpk(max)=1.0V/R
s
, and under the normal operating conditions the
COMP
ERROR
AMP
1
3
5
GND
CURRENT
SENSE
Rs
R
C
2R
R
IV
I
Ipeak =
R(V pin1 - 2V be)
3R x Rs
0.5mA
2
+
-
1
Zf
Zt
2.50V
V in
COMP
S3842P
8
Rt
Ct
4
5
LARGE Rt
SMALL Ct
SMALL Rt
LARGE Ct
Vpin4
INTERNAL
CLOCK
INTERNAL
CLOCK
Vpin4
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