UC3843B

Part: UC3842B, UC3843B series

Type: Fixed Frequency Current Mode Controller

Description: High performance fixed frequency current mode controller operating up to 500 kHz with a 1.0 A totem pole output, designed for Off-Line and DC-DC converter applications.

Operating Conditions:

• Supply voltage: 7.6–30 V (depending on variant)
• Operating temperature: -40 to +105 °C (for UC3842BV, UC3843BV variants)
• Current mode operation frequency: up to 500 kHz

Absolute Maximum Ratings:

• Max supply voltage: 30 V (V CC, V C)
• Max continuous current: 1.0 A (Output Current, Source or Sink)
• Max junction temperature: +150 °C

Key Specs:

• Reference Output Voltage: 5.0 V (typ, I O = 1.0 mA, T J = 25 ° C)
• Oscillator Frequency: 250 kHz (typ, R T = 6.2 k, C T = 1.0 nF, T J = 25 ° C)
• Error Amp Open Loop Voltage Gain: 90 dB (typ)
• Error Amp Unity Gain Bandwidth: 1.0 MHz (typ, T J = 25 ° C)
• Maximum Current Sense Input Threshold: 1.0 V (typ)
• Output Voltage Low State: 0.1 V (typ, I Sink = 20 mA)
• Startup Threshold (V CC ): 16 V (typ, UCX842B); 8.4 V (typ, UCX843B)
• Power Supply Current (Operating): 12 mA (typ)

Features:

• Oscillator Frequency Guaranteed at 250 kHz
• Trimmed Oscillator for Precise Frequency Control
• Current Mode Operation to 500 kHz
• Latching PWM for Cycle-By-Cycle Current Limiting
• Automatic Feed Forward Compensation
• Internally Trimmed Reference with Undervoltage Lockout
• Undervoltage Lockout with Hysteresis
• High Current Totem Pole Output
• Low Startup and Operating Current
• Pb-Free and Halide-Free Device

Applications:

• Off-Line converters
• DC-DC converter applications

Package:

• PDIP-8
• SOIC-8
• SOIC-14

• Oscillator Frequency Guaranteed at 250 kHz
• Trimmed Oscillator for Precise Frequency Control
• Current Mode Operation to 500 kHz
• Latching PWM for Cycle -By -Cycle Current Limiting
• Automatic Feed Forward Compensation
• Internally Trimmed Reference with Undervoltage Lockout
• Undervoltage Lockout with Hysteresis
• High Current Totem Pole Output
• Low Startup and Operating Current
• This is a Pb -Free and Halide -Free Device

Pin numbers in parenthesis are for the D suffix SOIC -14 package.

Figure 1. Simplified Block Diagram

PDIP -8 N SUFFIX CASE 626

SOIC -14 D SUFFIX CASE 751A

SOIC -8 D1 SUFFIX CASE 751

1

8 - Pin	14 - Pin	Function	Description
1	1	Compensation	This pin is the Error Amplifier output and is made available for loop compensation.
2	3	Voltage Feedback	This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider.
3	5	Current Sense	A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction.
4	7	R T /C T	The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor R T to V ref and capacitor C T to ground. Operation to 500 kHz is possible.
5		GND	This pin is the combined control circuitry and power ground.
6	10	Output	This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced and sunk by this pin.
7	12	V CC	This pin is the positive supply of the control IC.
8	14	V ref	This is the reference output. It provides charging current for capacitor C T through resistor R T .
	8	Power Ground	This pin is a separate power ground return that is connected back to the power source. It is used to reduce the effects of switching transient noise on the control circuitry.
	11	V C	The Output high state (V OH ) is set by the voltage applied to this pin. With a separate power source connection, it can reduce the effects of switching transient noise on the control circuitry.
	9	GND	This pin is the control circuitry ground return and is connected back to the power source ground.
	2,4,6,1 3	NC	No connection. These pins are not internally connected.

Figure 15. Output Waveform

Figure 17. Supply Current versus Supply Voltage

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Rating	Symbol	Value	Unit
Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec)	V CC , V C	30	V
Total Power Supply and Zener Current	(I CC + I Z )	30	mA
Output Current, Source or Sink	I O	1.0	A
Output Energy (Capacitive Load per Cycle)	W	5.0	m J
Current Sense, Voltage Feedback, V ref and Rt/Ct Inputs	V in	- 0.3 to + 5.5	V
Compensation	V comp	- 0.3 to + 7.2	V
Output	V o	- 0.3 to V CC or V C + 0.3	V
Error Amp Output Sink Current	I O	10	mA
Power Dissipation and Thermal Characteristics D Suffix, Plastic Package, SOIC - 14 Case 751A Maximum Power Dissipation@T A = 25 ° C Thermal Resistance, Junction - to - Air D1 Suffix, Plastic Package, SOIC - 8 Case 751 Maximum Power Dissipation@T A = 25 ° C Thermal Resistance, Junction - to - Air N Suffix, Plastic Package, Case 626 Maximum Power Dissipation@T A = 25 ° C Thermal Resistance, Junction - to - Air	P D R q JA P D R q JA P D R q JA	862 145 702 178 1.25 100	mW ° C/W mW ° C/W W ° C/W
Operating Junction Temperature	T J	+150	° C
Operating Ambient Temperature UC3842B, UC3843B UC2842B, UC2843B UC2843D UC3842BV, UC3843BV	T A	0 to 70 - 25 to + 85 - 40 to +85 - 40 to +105	° C
Storage Temperature Range	T stg	- 65 to +150	° C

Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected.

1. This device series contains ESD protection and exceeds the following tests: Human Body Model 4000 V per JEDEC Standard JESD22-A114B Machine Model Method 200 V per JEDEC Standard JESD22-A115-A

2. This device contains latch-up protection and exceeds 100 mA per JEDEC Standard JESD78

ELECTRICAL CHARACTERISTICS (V CC = 15 V [Note 3], R T = 10 k, C T = 3.3 nF. For typical values T A = 25 ° C, for min/max values TA is the operating ambient temperature range that applies [Note 4], unless otherwise noted.)

		UC284XB, UC2843D	UC284XB, UC2843D	UC284XB, UC2843D	UC384XB, XBV	UC384XB, XBV	UC384XB, XBV
Characteristics	Symbol	Min	Typ	Max	Min	Typ	Max
REFERENCE SECTION
Reference Output Voltage (I O = 1.0 mA, T J = 25 ° C)	V ref	4.95	5.0	5.05	4.9	5.0	5.1
Line Regulation (V CC = 12 V to 25 V)	Reg line	-	2.0	20	-	2.0	20
Load Regulation (I O = 1.0 mA to 20 mA)	Reg load	-	3.0	25	-	3.0	25
Temperature Stability	T S	-	0.2	-	-	0.2	-
Total Output Variation over Line, Load, and Temperature UC284XB UC2843D	V ref	4.9 4.82	- -	5.1 5.18	4.82	-	5.18
Output Noise Voltage (f = 10 Hz to 10 kHz, T J = 25 ° C)	V n	-	50	-	-	50	-
Long Term Stability (T A = 125 ° C for 1000 Hours)	S	-	5.0	-	-	5.0	-
Output Short Circuit Current	I SC	- 30	- 85	- 180	- 30	- 85	- 180
OSCILLATOR SECTION
Frequency T J = 25 ° C T A = T low to T high T J = 25 ° C (R T = 6.2 k, C T = 1.0 nF)	f OSC	49 48 225	52 - 250	55 56 275	49 48 225	52 - 250	55 56 275
Frequency Change with Voltage (V CC = 12 V to 25 V)	D f OSC / D V	-	0.2	1.0	-	0.2	1.0
Frequency Change with Temperature, T A = T low to T high	D f OSC / D T	-	1.0	-	-	0.5	-
Oscillator Voltage Swing (Peak - to - Peak)	V OSC	-	1.6	-	-	1.6	-
Discharge Current (V OSC = 2.0 V) T J = 25 ° C, T A = T low to T high UC284XB, UC384XB UC2843D, UC384XBV	I dischg	7.8 7.5 -	8.3 - -	8.8 8.8 -	7.8 7.6 7.2	8.3 - -	8.8 8.8 8.8
ERROR AMPLIFIER SECTION
Voltage Feedback Input (V O = 2.5 V) UC284XB UC2843D	V FB	2.45 2.42	2.5 2.5	2.55 2.58	2.42	2.5	2.58
Input Bias Current (V FB = 5.0 V)	I IB	-	- 0.1	- 1.0	-	- 0.1	- 2.0
Open Loop Voltage Gain (V O = 2.0 V to 4.0 V)	A VOL	65	90	-	65	90	-
Unity Gain Bandwidth (T J = 25 ° C)	BW	0.7	1.0	-	0.7	1.0	-
Power Supply Rejection Ratio (V CC = 12 V to 25 V)	PSRR	60	70	-	60	70	-
Output Current Sink (V O = 1.1 V, V FB = 2.7 V) Source (V O = 5.0 V, V FB = 2.3 V)	I Sink I Source	2.0 - 0.5	12 - 1.0	- -	2.0 - 0.5	12 - 1.0	- -
Output Voltage Swing High State (R L = 15 k to ground, V FB = 2.3 V) Low State (R L = 15 k to V ref , V FB = 2.7 V)	V OH V OL	5.0	6.2	-	5.0	6.2	-
UC284XB, UC384XB UC2843D, UC384XBV		- -	0.8 -	1.1 -	- -	0.8 0.8	1.1 1.2

		UC284XB, UC2843D	UC284XB, UC2843D	UC284XB, UC2843D	UC384XB, XBV	UC384XB, XBV	UC384XB, XBV
Characteristics	Symbol	Min	Typ	Max	Min	Typ	Max
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 5 and 6) UC2843D, UC284XB, UC384XB UC384XBV	A V	2.85 -	3.0 -	3.15 -	2.85 2.85	3.0 3.0	3.15 3.25
Maximum Current Sense Input Threshold (Note 5) UC2843D, UC284XB, UC384XB UC384XBV	V th	0.9 -	1.0 -	1.1 -	0.9 0.85	1.0 1.0	1.1 1.1
Power Supply Rejection Ratio (V CC = 12 V to 25 V, Note 5)	PSRR	-	70	-	-	70	-
Input Bias Current	I IB	-	- 2.0	- 10	-	- 2.0	- 10
Propagation Delay (Current Sense Input to Output)	t PLH(In/Out)	-	150	300	-	150	300
OUTPUT SECTION
Output Voltage Low State (I Sink = 20 mA) (I Sink = 200 mA) UC284XB, UC384XB UC384XBV, UC2843D High State (I Source = 20 mA) UC284XB, UC384XB UC384XBV, UC2843D (I Source = 200 mA)	V OL V OH	- - - 13 - 12	0.1 1.6 - 13.5 - 13.4	0.4 2.2 - - - -	- - - 13 12.9 12	0.1 1.6 1.6 13.5 13.5 13.4	0.4 2.2 2.3 - - -
Output Voltage with UVLO Activated (V CC = 6.0 V, I Sink = 1.0 mA)	V OL(UVLO)	-	0.1	1.1	-	0.1	1.1
Output Voltage Rise Time (C L = 1.0 nF, T J = 25 ° C)	t r	-	50	150	-	50	150
Output Voltage Fall Time (C L = 1.0 nF, T J = 25 ° C)	t f	-	50	150	-	50	150
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold (V CC ) UCX842B, BV UCX843B, BV, D	V th	15 7.8	16 8.4	17 9.0	14.5 7.8	16 8.4	17.5 9.0
Minimum Operating Voltage After Turn - On (V CC ) UCX842B, BV UCX843B, BV, D	V CC(min)	9.0 7.0	10 7.6	11 8.2	8.5 7.0	10 7.6	11.5 8.2
PWM SECTION
Duty Cycle Maximum UC284XB, UC384XB, UC2843D Maximum UC384XBV Minimum	DC (max) DC (min)	94 - -	96 - -	- - 0	94 93 -	96 96 -	- - 0
TOTAL DEVICE
Power Supply Current Startup (V CC = 6.5 V for UCX843B, UC2843D Startup V CC 14 V for UCX842B, BV)	I CC + I C	-	0.3	0.5	-	0.3	0.5
(Note 7)		-	12	17	-	12	17
Power Supply Zener Voltage (I CC = 25 mA)	V Z	30	36	-	30	36	-

Figure 2. Timing Resistor versus Oscillator Frequency

Figure 2. Timing Resistor versus Oscillator Frequency

Figure 4. Oscillator Discharge Current versus Temperature

Figure 6. Error Amp Small Signal Transient Response

Figure 3. Output Deadtime versus Oscillator Frequency

Figure 5. Maximum Output Duty Cycle versus Timing Resistor

Figure 7. Error Amp Large Signal Transient Response

Figure 8. Error Amp Open Loop Gain and Phase versus Frequency

Figure 10. Reference Voltage Change versus Source Current

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Figure 12. Reference Load Regulation

Figure 9. Current Sense Input Threshold versus Error Amp Output Voltage

Figure 11. Reference Short Circuit Current versus Temperature

Figure 13. Reference Line Regulation

Figure 14. Output Saturation Voltage versus Load Current

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Figure 16. Output Cross Conduction