Description

The 3842A(AM)/43A(AM)/44A(AM)/45A(AM) are fixed frequency current mode PWM controller. They are specially designed for
OFF−Line and DC to DC converter applications with a minimal 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,
and a high current totempole output ideally suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout
and current limiting. The 3842A(AM) and 3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding
thresholds for the 3843A(AM)/45A(AM) are 8.4V (on) and 7.6V (off). The MIK3842A(AM) and MIK3843A(AM) can operate within 100% duty
cycle. The 3844A(AM) and UC3845A(AM) can operate within 50% duty cycle.
The 384XA(AM) has Start-Up Current 0.17mA (typ).

Features Pin Connection

• Low Start-Up and Operating Current
• High Current Totem Pole Output
• Undervoltage Lockout With Hysteresis
•Operating Frequency Up To 300KHz (384XA)
500KHz (384XAM)

Top view
Block diagram
(toggle flip flop used only in MIK3844, MIK3845)

7
36V
5V SET/ GND
V VREF RESET
8 5
UVLO

VRE GOOD
F
LOGIC
INTERNAL
BIAS
POWER VCC
7
1/2 VREF

+ 2R

2 VFB ERR C.S.

COMP
1V R
OUT
R PWM
COMP LATCH 6
1
CURRENT S
SENSE
3
T
R /C 5
T OSCILLATOR
POWER GND

Absolute Maximum Ratings

Symbol Parameter Maximum Units

VCC Supply Voltage (low impedance source) 30 V

IO Output Current ±1 A
VI Input Voltage (Analog Inputs pins 2,3) −0.3 to 5.5 V
ISINK (E.A) Error Amp Output Sink Current 10 mA
Po Power Dissipation (TA=250C) 1 W
o
Tstg Storage Temperature Range -65 to150 C
TL Lead Temperature (soldering 5 sec.) 260 o
C

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1
Electrical characteristics
(*VCC=15V, RT=10kΩ, CT=3.3nF, TA=00C to +700C, unless otherwise specified)
Characteristics Symbol Test Conditions Min Typ Max Units
Reference Section
Reference Output Voltage VREF TJ = 25°C, IREF = 1 mA 4.9 5.0 5.1 V
Line Regulation ∆VREF 12V ≤ VCC ≤ 25 V 6.0 20 mV
Load Regulation ∆VREF 1 mA ≤ IREF ≤ 20mA 6.0 25
Short Circuit Output Current ISC TA = 25°C -100 -180 mA
Oscillator Section
f TJ = 25°C MIK384XA 47 50 57
Oscillation Frequency KHz
MIK384XAM 47 52 57
Frequency Change with Voltage ∆f/∆VCC 12V ≤ VCC ≤ 25 V 0.05 1.0 %
Oscillator Amplitude V(OSC) (peak to peak) 1.6 V
Error Amplifier Section
Input Bias Current IBIAS VFB=3V -0.1 -2 µA
Input Voltage VI(E.A) Vpin1 = 2.5V 2.42 2.5 2.58 V
Open Loop Voltage Gain AVOL 2V ≤ V0 ≤ 4V 65 90
dB
Power Supply Rejection Ratio PSRR 12V ≤ VCC ≤ 25 V 60 70
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
V
Low Output Voltage VOL Vpin2 = 2.7V, RL = 15KΩ to PIN 8 0.8 1.1
Current Sense Section
Gain GV (Note 1 & 2) 2.85 3.0 3.15 V/V
Maximum Input Signal VI(MAX) V pin1 = 5V (Note1) 0.9 1.0 1.1 V
Supply Voltage Rejection SVR 12V ≤ VCC ≤ 25 V (Note 1) 70 dB
Input Bias Current IBIAS Vpin3 = 3V -3.0 -10 µA
Output Section
Low Output Voltage VOL ISINK = 20 mA 0.08 0.4
ISINK = 200 mA 1.4 2.2
V
High Output Voltage VOH ISINK = 20 mA 13 13.5
ISINK = 200 mA 12 13.0
Rise Time tR TJ = 25°C, CL = 1nF (Note 3) 45 150
nS
Fall Time tF TJ = 25°C, CL = 1nF (Note 3) 35 150
Undervoltage Lockout Section
Start Theshold VTH(ST) MIK3842A(AM)/44A(AM) 14.5 16.0 17.5
V
MIK3843A(AM)/45A(AM) 7.8 8.4 9.0
Min. Operating Voltage VOPR(min) MIK3842A(AM)/44A(AM) 8.5 10 11.5
V
(After Turn On) MIK3843A(AM)/45A(AM) 7.0 7.6 8.2
PWM Section
Max. Duty Cycle D(MAX) MIK3842A(AM)/43A(AM) 95 97 100
MIK3844A(AM)/45A(AM) 47 48 50 %
Min. Duty Cycle D(MAX) 0
Total Standby Current
Start−Up Current IST MIK384XA(AM) 0.17 0.3
mA
Operating Supply Current ICC (OPR) Vpin3 = Vpin2 = 0V 13 17
Zener Voltage VZ ICC=25 mA 30 38 V
* - 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.

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Pin functions
N 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 normall y 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 R T 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 sink 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 C T through resistor RT .

Application information
2.5V
1mA

VFB 2

COMP 1

Figure 1. Error Amp Configuration

VCC 7
ON/OFF COMMAND TO S/R OF IC
ICC

MIK3842 MIK3843 13mA

MIK3844 MIK3845
VON 16V 8.4V

VOFF 10V 7.6V 0.2mA

VCC
VOFF VON
During UVLO, the Output is low

Figure 2. Undervoltage Lockout

ERROR
+ AMP 2R
2
VFB _
1V CURRENT
COMP 1
R SENSE
IS COMPARATOR
R
CURRENT 3
SENSE
RS C
5
GND

1.0V
Peak current is determined by IS max
RS

Figure 3. Current Sense Circuit

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 VREF VREF
8 8
RT RT
RT /CT RT /CT
4 4
RSLOPE MIK3842 RSLOPE MIK3842
IS IS
R1 ISENSE R1 ISENSE
3 3
5 5
RS RS
GND GND

Figure 4. Slope Compensation Techniques

SCR must be selected for a holding current of less than 0.5mA.

The simple two transistor circuit can be used in place of the SCR as shown.

Figure 5. Latched Shutdown

From V0
From V0
+ +
2.5 V 2.5 V
1mA Rp 1mA
RI + 2R + 2R
VFB RI VFB
- -
2 EA 2 EA
Cp
Rd Cf Rf
Rf Cf
R R
1
COMP 1
COMP
5 5
Error Amp compensation circuit for stabilizing any current-mode topology except for Error Amp compensation circuit for stabilizing current-mode boost and flyback
boost and flyback converters operating with continuous inductor current. topologies operating with continuous inductor current.

Figure 6. Error Amplifier Compensation

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Figure 7. External Clock Synchronization

Figure 8. Soft-Start Circuit

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 Typical Performance Characteristics
RT
(K %
)Ω
50 50 2nF
C

C 1nF

C 5nF 30 C 5nF

20 20 C 500pF
C 10nF

10 10

C 200pF

5 5
C 100pF
C 10nF
3

VCC = 15 V
2 VCC = 15 2 O
O
25 T = 25
T
C
1
1
10
500
20 30 50 100 200 300
f KHz) 10 20 30 50 100 200 300
f KHz)
500
Figure 1. Timing Resistor vs. Oscillator Frequency. Figure 2. Output Dead-Time vs. Oscillator Frequenc .y
Dm ax
(%) (dB)

VCC = 15 V
90 80
VO = 2V to 4V
R 100K
=
L 25
O
C
80 60

70 40

60 20
V 15 V
=
CC 3.3nF

50 T = 25
0

40 -20
1 2 3 5 10 100 1K 10K 100K 1M
R (T f (Hz)
Figure 3. Maximum Output Duty Cycle vs. Figure 4. Error Amp Open-Loop Gain vs.
Timing Resistor (MIK3842/4 .3) Fr . quency
e
Vth ISC
(V) (mA)

VCC = 15V VCC = 15 V

1.0 100

0.8 90

T 25 C
O

0.6 80
T 125 C
O

0.4 70

0.2 60

50
O

0 2 4 V (O 0 25 50 75 100 T )

Figure 5. Current Sense Input Threshold vs. Figure 6. Reference Short Circuit Current vs.
Error Amp Output Voltage. Temperature.

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Vsat ICC
(V) (m A)
Sourse Saturation
-1 (Load to Ground)

V 15 V

-2 80 sµ Pulsed Load 120Hz 20

Rate

3 15

2 10 I 0V
=
Se nse
0V
R 10K
Sink Sa tura tion
1 5 TA = 25
(Lo a d to C
C 3.3nF

0 0
0 200 400 600 I (O m 0 10 20 30 V (CC
Figure .7 Output Saturation Voltage vs. Load Figure .8 Supply Current vs. Supply
Current T Voltag .e
25 .

VCC
7
Vref 8 R /C
T T
5V REG
OUTPUT
PWM 6
RT OUTPUT LARGE R / SMALL C
T
CLOCK

4
R C
T OSCILLATOR
R /C
T T
/
T ID
OUTPUT

SMALL RT / LARGE
5
GND
Figure 9. Oscillator and Output Waveforms

Ordering Information
O RDERI NG NUM BER P ACK AG E M AR K I NG

3842 / 43 / 44/ 45 SOP -8 / DI P - 8 KA3842/ 43 / 44/ 45

Address : 6A06--6A07
Rm 6A07,Changyin Office Building ,No.88,Yong Ding Road,Hai Dian District ,Beijing
Postalcode:100039
Tel: 86-010-58895780 / 81 / 82 / 83 / 84 Fax : 010-58895793
Http://www.estek.com.cn
Email:sales@estek.com.cn

REV No:01-060815

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