简介

Description

The 3842/43/44/45 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 3842 and 3844 have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843/

45 are 8.4V (on) and 7.6V (off). The 3842) and 3843 can operate within 100% duty cycle. The 3844 and 3845 can operate within 50% duty cycle.

The 384X has Start-Up Current 0.5mA (typ).

Features

• Low Start-Up and Operating Current

• High Current Totem Pole Output

• Undervoltage Lockout With Hysteresis

• Operating Frequency Up To 500KHz

Pin Connection

Top view

Block diagram

(toggle flip flop used only in 3844, 3845)

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
Tstg	Storage Temperature Range		-65 to150	oC
TL	Lead Temperature (soldering 5 sec.)		260	oC
TA	Operating Ambient Temperature		0 to 70	oC

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Electrical characteristics

(*VCC=15V, RT=10kΩ, CT=3.3nF, TA=0℃to +70℃, 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
Oscillation Frequency	f	TJ = 25°C	384X	47	50	57	KHz -
			384X	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	V
		ISINK = 200 mA			1.4	2.2
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)	3842/44		14.5	16.0	17.5	V -
		3843/45		7.8	8.4	9.0
Min. Operating Voltage (After Turn On)	VOPR(min)	3842/44		8.5	10	11.5	V -
		3843/45		7.0	7.6	8.2
PWM Section
Max. Duty Cycle	D(MAX)	3842/43		95	97	100	%
		3844/45		47	48	50
Min. Duty Cycle	D(MAX)					0
Total Standby Current
Start-Up Current	IST	384X			0.05		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.

UMW

UMW UC3842/43/44/45

Pinfunctions

完整版