UNITRODE UCC1857, UCC2857, UCC3857 Technical data

UCC1857

UCC1857

UCC2857

UCC3857

Isolated Boost PFC Preregulator Controller

PRELIMINARY

FEATURES

∙PFC With Isolation, VO < VIN

∙Single Power Stage

∙Zero Current Switched IGBT

∙Programmable ZCS Time

∙Corrects PF to >0.99

∙Fixed Frequency, Average Current Control

∙Improved RMS Feedforward

∙Soft Start

∙9V to 18V Supply V Range

∙20-Pin DW, N, J, and L Packages

TYPICAL APPLICATION CIRCUIT

DESCRIPTION

The UCC3857 provides all of the control functions necessary for an Isolated Boost PFC Converter. These converters have the advantage of transformer isolation between primary and secondary, as well as an output bus voltage that is lower than the input voltage. By providing both power factor correction and down conversion in a single power processing stage, the UCC3857 is ideal for applications which require high efficiency, integration, and performance.

The UCC3857 brings together the control functions and drivers necessary to generate overlapping drive signals for external IGBT switches, and provides a separate output to drive an external power MOSFET which provides zero current switching (ZCS) for both the IGBTs. Full programmability is provided for the MOSFET driver delay time with an external RC network. ZCS for the IGBT switches alleviates the undesirable turn off losses typically associated with these devices. This allows for higher switching frequencies, smaller magnetic components and higher efficiency. The power factor correction (PFC) portion of the UCC3857 employs the familiar average current control scheme used in previous Unitrode controllers. Internal circuitry changes, however, have simplified the design of the PFC section and improved performance.

(continued)

RECTIFIED

AC INPUT

REF

RAC

ZV

			T1	+
				CF
BIAS	QA	Q1	Q2	VOUT
SUPPLY				–
RS
ZC				FEEDBACK
				CKT
				OPTO

			13					3								7						8			4						15
PKLMT MOUT															CA–						CAO				VIN						VD

1 IAC

MOSDRV 14

2

CRMS IGDRV1 16 UCC3857

10 VA–

IGDRV2 18

11 VAO

DELAY 12

REF

REF

5 VREF

SS						RT						CT					PGND					AGND
20						19						20						17						6

UDG-98065

02/99

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage (VIN, VD) . . . . . . . . . . . . . . . . . . . . . . 18V General Analog/Logic Inputs

(CRMS, MOUT, CA–, VA–, CT, RT, PKLMT)

(Maximum Forced Voltage). . . . . . . . . . . . . . . . –0.3V to 5V IAC (Maximum Forced Current) . . . . . . . . . . . . . . . . . . . 300μA Reference Output Current . . . . . . . . . . . . . . . Internally Limited Output Current (MOSDRV, IGDRV1, IGDRV2)

Pulsed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200mA Storage Temperature . . . . . . . . . . . . . . . . . . . −65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . −55°C to +150°C Lead Temperature (Soldering, 10 Sec.). . . . . . . . . . . . . +300°C

Unless otherwise indicated, voltages are reference to ground and currents are positive into, negative out of the specified terminal. Pulsed is defined as a less than 10% duty cycle with a maximum duration of 500 s. Consult Packaging Section of Databook for thermal limitations and considerations of packages.

UCC1857

UCC2857

UCC3857

DESCRIPTION (continued)

Controller improvements include an internal 6 bit A-D converter for RMS input line voltage detection, a zero load power circuit, and significantly lower quiescent operating current. The A-D converter eliminates an external 2 pole low pass filter for RMS detection.

This simplifies the converter design, eliminates 2nd harmonic ripple from the feedforward component, and provides an approximate 6 times improvement in input line transient response. The zero load power comparator prevents energy transfer during open load conditions without compromising power factor at light loads. Low startup and operating currents which are achieved through the use of Unitrode's BCDMOS process simplify the auxiliary bootstrap supply design.

Additional features include: under voltage lockout for reliable off-line startup, a programmable over current shutdown, an auxiliary shutdown port, a precision 7.5V reference, a high amplitude oscillator ramp for improved noise immunity, softstart, and a low offset analog square, multiple and divide circuit. Like previous Unitrode PFC controllers, worldwide operation without range switches is easily implemented.

CONNECTION DIAGRAMS

DIL-20, SOIC20 (Top View)										PLCC-20 (Top View)
J, N and DW Packages										L Package
IAC								CT		IAC
	1						20
										CRMS																																						CT
CRMS	2						19	RT		MOUT																																						RT
MOUT	3						18	IGDRV2									3						2			1						20								19
										VIN			4																											18								IGDRV2
VIN	4						17	PGND
										VREF			5																											17								PGND
VREF	5						16	IGDRV1
										AGND			6																											16								IGDRV1
AGND	6						15	VD		CA–			7																											15								VD
CA–	7						14	MOSDRV		CAO			8																											14								MOSDRV
CAO	8						13	PKLMT					9									10				11						12								13
										SS																																						PKLMT
SS	9						12	DELAY
										VA–																																						DELAY
VA–	10						11	VAO																																								VAO

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UCC1857

UCC2857

UCC3857

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = 0°C to 70°C for the UCC3857, –40°C to +85°C for the UCC2857, and –55°C to +125°C for the UCC1857, V VIN, VVD = 12V, RT = 19.2K, CT = 680pF. TA = TJ.

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNITS
Input Supply
Supply Current, Active	No Load on Outputs, VVD = VVIN		3.5	5	mA
Supply Current, Startup	No Load on Outputs, VVD = VVIN		60	TBD	μA
VIN UVLO Threshold			13.75	15.5	V
UVLO Threshold Hysteresis		3	3.75	TBD	V
Reference
Output Voltage (VVREF)	TJ = 25°C, I REF = 1mA	7.387	7.5	7.613	V
	Over Temperature, UCC3857	7.368	7.5	7.631	V
	Over Temperature, UCC1857, UCC2857	7.313	7.5	7.687	V
Load Regulation	IREF = 1mA to 10mA		2	10	mV
Line Regulation	VVIN = VVD = 12V to 16V		2	15	mV
Short Circuit Current	VVREF = 0V		–55	–30	mA
Current Amplifier
Input Offset Voltage	(Note 1)	–3	0	3	mV
Input Bias Current	(Note 1)		–50		nA
Input Offset Current	(Note 1)		25		nA
CMRR	VCM = 0V to 1.5V, VCAO = 3V		80		dB
AVOL	VCM = 0V, VCAO = 2V to 5V	65	85		dB
VOH	Load on CAO = 50μA, VMOUT = 1V, VCA– = 0V	6	7		V
VOL	Load on CAO = 50μA, VMOUT = 0V, VCA– = 1V		0.2		V
Maximum Output Current	Source : VCA– = 0V, VMOUT = 1V, VCAO = 3V		–150		μA
	Sink : VCA– = 1V, VMOUT = 0V, VCAO = 3V	5	30	50	mA
Gain Bandwidth Product	fIN = 100kHz, 10mV p – p	3	5		MHz
Voltage Amplifier
Input Voltage	Measured on VVA–, VVAO = 3V	2.9	3	3.1	V
Input Bias Current	Measured on VVA–, VVAO = 3V		–50		nA
AVOL	VVAO = 1V to 5V		75		dB
VOH	Load on VVAO= –50μA, VVA–= 2.8V	5.3	5.55	5.7	V
VOL	Load on VVAO= 50μA, VVA–= 3.2V		0.1	0.45	V
Maximum Output Current	Source: VVA– = 2.8V, VVAO = 3V	–20	–12	–5	mA
	Sink: VVA– = 3.2V, VVAO= 3V	5	20	30	mA
Oscillator
Initial Accuracy	TJ = 25°C	42.5	50	57.5	kHz
		40	50	60	kHz
Voltage Stability	VVIN = 12V to 18V		1		%
CT Ramp Peak-Valley Amplitude		4	4.5	5	V
CT Ramp Valley Voltage			1.5		V
Output Drivers
VOH	IL = –100mA	9	10		V
VOL	IL = 100mA		0.1	0.5	V
Rise Time	CLOAD = 1nF		25	TBD	ns
Fall Time	CLOAD = 1nF		10	TBD	ns
Trailing Edge Delay
Delay Time	RD = 12k, CD = 200pF, VVAO = 4V	1.6	2	2.4	μs

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