UNITRODE UCC1890, UCC2890, UCC3890 Technical data

UCC1890

UCC2890

UCC3890

Off-Line Battery Charger Circuit

FEATURES

∙Transformerless Off-Line Operation

∙Low Voltage Operation to 0.8V

∙Ideal for Battery Trickle Charger Applications

∙Current Mode Operation With 100mV Shunt

∙Voltage Mode Operation With Fixed 1.25V Output or Resistor Adjustable Output

∙Efficient BiCMOS Design

∙Inherent Short Circuit Protection

DESCRIPTION

The UCC3890 controller is optimized for use as an off-line, low power, low voltage, regulated current supply, ideally suited for battery trickle charger applications. The unique circuit topology used in this device can be visualized as two cascaded flyback converters; each operating in the discontinuous mode, and both driven from a single external power switch. The significant benefit of this approach is the ability to charge low voltage batteries in off-line applications with no transformer, and low internal losses.

The control algorithm used by the UCC3890 forces a switch on time inversely proportional to the input line voltage, while the switch off time is inversely proportional to the output voltage. This action is automatically controlled by an internal feedback loop and reference. The cascaded configuration allows a large voltage conversion ratio with reasonable switch duty cycle.

While the UCC3890 is ideally suited for control of constant current battery chargers, provision is also made to operate as a fixed 1.25V regulated supply, or to use a resistor voltage divider to obtain output voltages higher than 1.25V.

BLOCK DIAGRAM

Note: This device incorporates patented technology used under license from Lambda Electronics, Inc.

UDG-96052

3/97

ABSOLUTE MAXIMUM RATINGS

IDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5mA Current into TON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5mA

Voltage on VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20V

Current into TOFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250μA Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . –55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C

Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages.

UCC1890

UCC2890

UCC3890

CONNECTION DIAGRAMS

DIL-8, SOIC-8 (Top View)

J, N, or D Packages

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = –55°C to 125°C for UCC1890, –40°C to 85°C for the UCC2890, and 0°C to 70°C for the UCC3890. No load at DRIVE pin (C LOAD = 0), TA = TJ.

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNITS
General
VDD Zener Voltage	IDD = 4.75mA,ITON = 0mA	8.3	9.0	9.4	V
Minimum Operating Current ITON	IDD = –1mA, F = 150kHz		1.65	2.0	mA
Undervoltage Lockout
Minimum Voltage to Start	FB = 0	7.8	8.6	9.2	V
Minimum Voltage after Start	FB = 0	5.75	6.3	6.65	V
Hysteresis	FB = 0	1.8	2.3	2.6	V
VDD – VSTART	FB = 0	0.2	0.4	0.7	V
Oscillator
Amplitude	ITON = 3mA; ITOFF = 50μA; VFB = 0V CT = 100pF	3.1	3.4	3.7	V
CT to DRIVE High Delay	Overdrive = 200mV		80	200	ns
CT to DRIVE Low Delay	Overdrive = 200mV		50	100	ns
Charge Coefficient ICT/ITON	ITON = 3mA; VCT = 3.0V	0.135	0.15	0.165	μA/μA
Discharge Coefficent ICT/ITOFF	ITOFF = 50μA; VCT = 3.0V	0.95	1.00	1.05	μA/μA
Driver
VOL	I = 100mA (Note 1)		0.7	1.8	V
VOH	I = –100mA referred to VDD (Note 1)	–2.9	–1.5		V
Rise Time	CL = 1nF		35	70	ns
Fall Time	CL = 1nF		30	60	ns
Line Voltage Detection
Minimum ITON for Fault		1.0	1.5	2.0	mA
ITON Detector Hysteresis			110		μA
On Time During Fault			0.5		μs
VOUT Error Amplifier
Reference Level	ITOFF = 50μA, ICT = 25μA, TJ = 25°C	1.20	1.25	1.30	V
	ITOFF = 50μA, ICT = 25μA, Over Temperature	1.15	1.25	1.35	V
Voltage at TOFF	ITOFF = 50μA	0.3	0.4	0.5	V
Regulation gm	ITOFF = 50μA (Note 2)	2.0	4.0	7.7	mA/V
Current Sense Amplifier
Gain	VCS = 90 – 110mV	11.8	12.5	13.0	V/V
Input Offset Voltage	VCS = 90 – 110mV	–5	0	5	mV
Input Voltage for CS Amplifier Enabled	ITON = 3mA, Referred to VDD	–1.5	–0.8		V
Input Voltage for CS Amplifier Disabled	ITON = 3mA, Referred to VDD		–0.8	–0.3	V

Note 1: VDD forced to 100mV below VDD Zener Voltage

Note 2: gm is defined as ICT for the values of VFB where the error amp is in regulation. The two points used to calculate gm

VFB

are for ICT at 65% amd 35% of its maximum value.

PIN DESCRIPTIONS

CS: The high side of the current sense shunt is connected to this pin. Short CS to VDD for voltage feedback operation.

CT: Oscillator timing capacitor is connected to this pin.

DRIVE: Gate drive to external power switch.

FB: Output of current sense amplifier. This pin can be used for direct output voltage feedback if the current sense amp input pin CS is shorted to the VDD pin.

GND: Ground pin.

UCC1890

UCC2890

UCC3890

TOFF: Resistor ROFF connects from voltage output to this pin to provide a maximum capacitor discharge current proportional to output voltage.

TON: Resistor RON connects from line input to this pin to provide capacitor charge current proportional to line voltage. The current in RON also provides power for the 9V shunt regulator at VDD.

VDD: Output of 9V shunt regulator.

APPLICATION INFORMATION

UDG-96053

Figure 1. Typical Voltage Mode Application

OPERATION (VOLTAGE OUTPUT)

Figure 1 shows a typical voltage mode application. When input voltage is first applied, all of the current through RDD and 80% of the current through RON, charge the external capacitor C3 connected to VDD. As the voltage builds on VDD, undervoltage lockout holds the circuit off and the output DRIVE low until VDD reaches 8.4V. At this time, DRIVE goes high, turning on the external power switch Q1, and 15% of the current into TON is directed to the timing capacitor CT. The voltage at TON is fixed at approximately 11V, so CT charges to a fixed threshold with current

= ∙ VIN – 11V

I 0.2

RON

Since the input line is much greater than 11V, the charge current is approximately proportional to the input line voltage. DRIVE is only high while CT is charging, so

the power switch on time is inversely proportional to line voltage. This provides a constant line voltage-switch on time product.

At the end of the switch on time, Q1 is turned off, and the 15% of the RON current which was charging CT is diverted to ground. The power switch off time is controlled by discharge of CT, which is determined by the outut voltage as described here:

UDG-96054

+ 5 hidden pages