Motorola UC3845N, UC3845DR2, UC3845D, UC3844N, UC3844DR2 Datasheet

High Performance

Current Mode Controllers

The UC3844, UC3845 series are high performance fixed frequency current mode controllers. They are specifically designed for Off±Line and dc±to±dc converter applications offering the designer a cost effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.

Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle±by±cycle current limiting, a latch for single pulse metering, and a flip±flop which blanks the output off every other oscillator cycle, allowing output deadtimes to be programmed for 50% to 70%.

These devices are available in an 8±pin dual±in±line plastic package as well as the 14±pin plastic surface mount (SO±14). The SO±14 package has separate power and ground pins for the totem pole output stage.

The UCX844 has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off±line converters. The UCX845 is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

•Current Mode Operation to 500 kHz Output Switching Frequency

•Output Deadtime Adjustable from 50% to 70%

•Automatic Feed Forward Compensation

•Latching PWM for Cycle±By±Cycle Current Limiting

•Internally Trimmed Reference with Undervoltage Lockout

•High Current Totem Pole Output

•Input Undervoltage Lockout with Hysteresis

•Low Startup and Operating Current

•Direct Interface with Motorola SENSEFET Products

Simplified Block Diagram

			VCC 7(12)
Vref		5.0V	VCC
8(14)		Reference	Undervoltage
R			Lockout
R	Vref		VC
	Undervoltage		7(11)
	Lockout

	RTCT	Oscillator	Flip	Output
	4(7)			6(10)
			Flop
	Voltage		&	PWR GND
			Latching
	Feedback	+		5(8)
			PWM
	2(3)	±		Current
		Error
				Sense
	1(1)	Amplifier		3(5)
	Output
	Comp.	Gnd	5(9)

Pin numbers in parenthesis are for the D suffix SO±14 package.

Order this document by UC3844/D

UC3844, 45

UC2844, 45

HIGH PERFORMANCE

CURRENT MODE

CONTROLLERS

N SUFFIX

PLASTIC PACKAGE

CASE 626

	8
D SUFFIX	1
PLASTIC PACKAGE
CASE 751A	14
(SO±14)	1

PIN CONNECTIONS

Compensation			1				8		Vref
Voltage Feedback			2				7		VCC
Current Sense			3				6		Output
	RT/CT		4				5		Gnd
					(Top View)
Compensation		1					14		Vref
	NC	2					13		NC
Voltage Feedback		3					12		VCC
	NC	4					11		VC
Current Sense		5					10		Output
	NC	6					9		Gnd
	RT/CT								Power Ground
		7					8
					(Top View)
ORDERING INFORMATION
		Operating
Device	Temperature Range								Package
UC3844D									SO±14
UC3845D	TA = 0° to +70°C								SO±14
UC3844N									Plastic
UC3845N									Plastic
UC2844D									SO±14
UC2845D	TA = ± 25° to +85°C								SO±14
UC2844N									Plastic
UC2845N									Plastic

Motorola, Inc. 1996

Rev 1

UC3844, 45 UC2844, 45

MAXIMUM RATINGS

Rating

Symbol

Value

Unit

Total Power Supply and Zener Current

(ICC + IZ)

30

mA

Output Current, Source or Sink (Note 1)

IO

1.0

A

Output Energy (Capacitive Load per Cycle)

W

5.0

μJ

Current Sense and Voltage Feedback Inputs

Vin

± 0.3 to + 5.5

V

Error Amp Output Sink Current

IO

10

mA

Power Dissipation and Thermal Characteristics

D Suffix, Plastic Package, Case 751A

Maximum Power Dissipation @ TA = 25°C

PD

862

mW

Thermal Resistance Junction±to±Air

RθJA

145

°C/W

N Suffix, Plastic Package, Case 626

Maximum Power Dissipation @ TA = 25°C

PD

1.25

W

Thermal Resistance Junction±to±Air

RθJA

100

°C/W

Operating Junction Temperature

TJ

+ 150

°C

Operating Ambient Temperature

TA

°C

UC3844, UC3845

0 to + 70

UC2844, UC2845

± 25 to + 85

Storage Temperature Range

Tstg

± 65 to + 150

°C

ELECTRICAL CHARACTERISTICS (VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3],

unless otherwise noted.)

UC284X

UC384X

Characteristics

Symbol

Min

Typ

Max

Min

Typ

Max

Unit

REFERENCE SECTION

Reference Output Voltage (IO = 1.0 mA, TJ = 25°C)

Vref

4.95

5.0

5.05

4.9

5.0

5.1

V

Line Regulation (VCC = 12 V to 25 V)

Regline

±

2.0

20

±

2.0

20

mV

Load Regulation (IO = 1.0 mA to 20 mA)

Regload

±

3.0

25

±

3.0

25

mV

Temperature Stability

TS

±

0.2

±

±

0.2

±

mV/°C

Total Output Variation over Line, Load, Temperature

Vref

4.9

±

5.1

4.82

±

5.18

V

Output Noise Voltage (f = 10 Hz to kHz, TJ = 25°C)

Vn

±

50

±

±

50

±

μV

Long Term Stability (TA = 125°C for 1000 Hours)

S

±

5.0

±

±

5.0

±

mV

Output Short Circuit Current

ISC

± 30

± 85

± 180

± 30

± 85

± 180

mA

OSCILLATOR SECTION

Frequency

fosc

kHz

TJ = 25°C

47

52

57

47

52

57

TA = Tlow to Thigh

46

±

60

46

±

60

Frequency Change with Voltage (VCC = 12 V to 25 V)

fosc/

V

±

0.2

1.0

±

0.2

1.0

%

Frequency Change with Temperature

fosc/

T

±

5.0

±

±

5.0

±

%

TA = Tlow to Thigh

Oscillator Voltage Swing (Peak±to±Peak)

Vosc

±

1.6

±

±

1.6

±

V

Discharge Current (Vosc = 2.0 V, TJ = 25°C)

Idischg

±

10.8

±

±

10.8

±

mA

NOTES: 1. Maximum Package power dissipation limits must be observed.

2.Adjust VCC above the Startup threshold before setting to 15 V.

3.Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible

Tlow = 0°C for UC3844, UC3845	Thigh = +70°C for UC3844, UC3845
±25°C for UC2844, UC2845	+85°C for UC2844, UC2845

2	MOTOROLA ANALOG IC DEVICE DATA

5. Comparator gain is defined as: AV

UC3844, 45 UC2844, 45

ELECTRICAL CHARACTERISTICS (VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3], unless otherwise noted,)

				UC284X			UC384X
	Characteristics	Symbol	Min	Typ	Max	Min	Typ	Max	Unit
ERROR AMPLIFIER SECTION
Voltage Feedback Input (VO = 2.5 V)		VFB	2.45	2.5	2.55	2.42	2.5	2.58	V
Input Bias Current (VFB = 2.7 V)		IIB	±	±0.1	±1.0	±	±0.1	±2.0	μA
Open Loop Voltage Gain (VO = 2.0 V to 4.0 V)		AVOL	65	90	±	65	90	±	dB
Unity Gain Bandwidth (TJ = 25°C)		BW	0.7	1.0	±	0.7	1.0	±	MHz
Power Supply Rejection Ratio (VCC = 12 V to 25 V)		PSRR	60	70	±	60	70	±	dB
Output Current									mA
Sink (VO = 1.1 V, VFB = 2.7 V)		ISink	2.0	12	±	2.0	12	±
Source (VO = 5.0 V, VFB = 2.3 V)		ISource	±0.5	±1.0	±	±0.5	±1.0	±
Output Voltage Swing									V
High State (RL = 15 k to ground, VFB = 2.3 V)		VOH	5.0	6.2	±	5.0	6.2	±
Low State (RL = 15 k to Vref, VFB = 2.7 V)		VOL	±	0.8	1.1	±	0.8	1.1
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)		AV	2.85	3.0	3.15	2.85	3.0	3.15	V/V
Maximum Current Sense Input Threshold (Note 4)		Vth	0.9	1.0	1.1	0.9	1.0	1.1	V
Power Supply Rejection Ratio		PSRR							dB
VCC = 12 V to 25 V (Note 4)			±	70	±	±	70	±
Input Bias Current		IIB	±	±2.0	±10	±	±2.0	±10	μA
Propagation Delay (Current Sense Input to Output)		tPLH(IN/OUT)	±	150	300	±	150	300	ns
OUTPUT SECTION
Output Voltage									V
Low State	(ISink = 20 mA)	VOL	±	0.1	0.4	±	0.1	0.4
	(ISink = 200 mA)		±	1.6	2.2	±	1.6	2.2
High State	(ISink = 20 mA)	VOH	12	13.5	±	13	13.5	±
	(ISink = 200 mA)		12	13.4	±	12	13.4	±
Output Voltage with UVLO Activated		VOL(UVLO)							V
VCC = 6.0 V, ISink = 1.0 mA			±	0.1	1.1	±	0.1	1.1
Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C)		tr	±	50	150	±	50	150	ns
Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C)		tf	±	50	150	±	50	150	ns
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold		Vth							V
UCX844			15	16	17	14.5	16	17.5
UCX845			7.8	8.4	9.0	7.8	8.4	9.0
Minimum Operating Voltage After Turn±On		VCC(min)							V
UCX844			9.0	10	11	8.5	10	11.5
UCX845			7.0	7.6	8.2	7.0	7.6	8.2
PWM SECTION
Duty Cycle									%
Maximum		DCmax	46	48	50	47	48	50
Minimum		DCmin	±	±	0	±	±	0
TOTAL DEVICE
Power Supply Current (Note 2)		ICC							mA
Startup:
(VCC = 6.5 V for UCX845A,			±	0.5	1.0	±	0.5	1.0
14 V for UCX844) Operating			±	12	17	±	12	17
Power Supply Zener Voltage (ICC = 25 mA)		VZ	30	36	±	30	36	±	V

NOTES: 2. Adjust VCC above the Startup threshold before setting to 15 V.

3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible

Tlow = 0°C for UC3844, UC3845	Thigh = +70°C for UC3844, UC3845
±25°C for UC2844, UC2845	+85°C for UC2844, UC2845

4. This parameter is measured at the latch trip point with VFB = 0 V. V Output Compensation

V Current Sense Input

MOTOROLA ANALOG IC DEVICE DATA	3

UC3844, 45 UC2844, 45

Figure 1. Timing Resistor versus	Figure 2. Output Deadtime versus
Oscillator Frequency	Oscillator Frequency

	100						VCC = 15 V
)(kRESISTORΩ								DEADTIMEOUTPUT
	50						TA = 25°C
	20
T	10							PERCENT
TIMING,	5.0
R	2.0	NOTE: Output switches						DT,
		at one±half the oscillator						%
		frequency.
	1.0
	10 k		20 k	50 k	100 k	200 k	500 k	1.0 M

75
70													1.0	nF
											2.0	nF
65									5.0 nF
					CT = 10	nF
60
55
													100	pF
										500 pF			200 pF
50

10 k 20 k 50 k 100 k 200 k 500 k 1.0 M

fosc, OSCILLATOR FREQUENCY (Hz)

fosc, OSCILLATOR FREQUENCY (Hz)

Figure 3. Error Amp Small Signal

Transient Response

VCC = 15 V

2.55 V AV = ±1.0

TA = 25°C

2.5V

2.45V

0.5 μs/DIV

20 mV/DIV

Figure 4. Error Amp Large Signal

Transient Response

VCC = 15 V

3.0 V AV = ±1.0

TA = 25°C

2.5 V

2.0 V

1.0 μs/DIV

200 mV/DIV

Figure 5. Error Amp Open Loop Gain and	Figure 6. Current Sense Input Threshold
Phase versus Frequency	versus Error Amp Output Voltage

(dB)	100						0		(V)	1.2
					VCC = 15 V			PHASEEXCESS,φ (DEGREES)	SENSECURRENTINPUT THRESHOLD		VCC = 15 V
VOL					VO = 2.0 V to 4.0 V
GAIN	80		Gain		RL = 100 K		30			1.0
VOLTAGE	60				TA = 25°C		60			0.8
											TA = 25°C
LOOP	40						90			0.6	TA = 125°C
						Phase
, OPEN	20						120			0.4		TA = ±55°C
	0						150			0.2
A	± 20						180		,
									th	0
	10	100	1.0 k	10 k	100 k	1.0 M	10 M		V		2.0	4.0	6.0	8.0
										0
			f, FREQUENCY (Hz)								VO, ERROR AMP OUTPUT VOLTAGE (V)

4	MOTOROLA ANALOG IC DEVICE DATA

UC3844, 45 UC2844, 45

Figure 7. Reference Voltage Change

versus Source Current

(mV)	0
CHANGE						VCC = 15 V
	±4.0
VOLTAGE	±8.0
	±12
, REFERENCE
	±16		TA = 125°C		TA = ±55°C
	±20			TA = 25°C
ref
V	±24
	0	20	40	60	80	100	120
		Iref, REFERENCE SOURCE CURRENT (mA)

			Figure 8. Reference Short Circuit Current
	(mA)			versus Temperature
		110
	CURRENT
								VCC = 15 V
								RL ≤ 0.1 Ω
	SHORT CIRCUIT	90
		70
	, REFERENCE
		50
	SC
		±55	±25	0	25	50	75	100	125
	I
				TA, AMBIENT TEMPERATURE (°C)

OUTPUT, CHANGEVOLTAGE mV/DIV)(2.0

O V

Figure 9. Reference Load Regulation

VCC = 15 V

IO = 1.0 mA to 20 mA

TA = 25°C

2.0 ms/DIV

OUTPUT, CHANGEVOLTAGE mV/DIV)(2.0

O V

Figure 10. Reference Line Regulation

VCC = 12 V to 25 V

TA = 25°C

2.0 ms/DIV

Figure 11. Output Saturation Voltage

versus Load Current

(V)	0	VCC	Source Saturation	VCC = 15 V
VOLTAGE
	±1.0	TA = 25°C	(Load to Ground)	80 μs Pulsed Load
				120 Hz Rate
	±2.0
SATURATION			TA = ±55°C
	3.0
		TA = ±55°C
, OUTPUT	2.0
				TA = 25°C
	1.0
sat			Sink Saturation
				Gnd
			(Load to VCC)
V
	0
	0	200	400	600	800

IO, OUTPUT LOAD CURRENT (mA)

Figure 12. Output Waveform

VCC = 15 V

CL = 1.0 nF

90% ° TA = 25 C

10%

50 ns/DIV

MOTOROLA ANALOG IC DEVICE DATA	5