ETC UCC3889N

UCC1889
UCC2889
UCC3889
Off-line Power Supply Controller
FEATURES
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DESCRIPTION
Transformerless Off-line
Applications
The UCC1889 controller is optimized for use as an off-line, low power, low voltage,
regulated bias supply. The unique circuit topology utilized in this device can be
visualized as two cascaded flyback converters, each operating in the discontinuIdeal Primary-side Bias Supply
ous mode, and both driven from a single external power switch. The significant
Efficient BiCMOS Design
benefit of this approach is the ability to achieve voltage conversion ratios of 400V
to 12V with no transformer and low internal losses.
Wide Input Range
The control algorithm utilized by the UCC1889 is to force the switch on time to be
Fixed or Adjustable
inversely proportional to the input line voltage while the switch off time is made inLow Voltage Output
versely proportional to the output voltage. This action is automatically controlled by
Uses Low Cost SMD Inductors an internal feedback loop and reference. The cascaded configuration allows a voltage conversion from 400V to 12V to be achieved with a switch duty cycle greater
Short Circuit Protected
than 10%. This topology also offers inherent short circuit protection since as the
output voltage falls to zero, the switch off time approaches infinity.
Optional Isolation Capability
The output voltage can be easily set to 12V or 18V. Moreover, it can be programmed for other output voltages less than 18V with a few additional components. An isolated version can be achieved with this topology as described further
in Unitrode Application Note U-149.
OPERATION
With reference to the application diagram below, when input voltage is first applied,
the RON current into TON is directed to VCC where it charges the external capacitor,
C3, connected to VCC. As voltage builds on VCC, an internal undervoltage lockout
holds the circuit off and the output at DRIVE low until VCC reaches 8.4V. At this
time, DRIVE goes high turning on the power switch, Q1, and redirecting the current
into TON to the timing capacitor, CT. CT charges to a fixed threshold with a current
ICHG=0.8 • (VIN - 4.5V)/RON. Since DRIVE will only be high for as long as CT
charges, the power switch on time will be inversely proportional to line voltage.
This provides a constant line voltage-switch on time product.
TYPICAL APPLICATION
Note: This device incorporates patented technology used under license from Lambda Electronics, Inc.
2/95
UDG-93060-1
UCC1889
UCC2889
UCC3889
OPERATION (cont.)
At the end of the on time, Q1 is turned off and the RON
current into TON is again diverted to VCC. Thus the current through RON, which charges CT during the on time,
contributes to supplying control power during the off time.
IDCHG = (VOUT - 0.7V) / ROFF
As VOUT increases, IDCHG increases resulting in the
reduction of off time. The frequency of operation increases and VOUT rises quickly to its regulated value.
The power switch off time is controlled by the discharge
of CT which, in turn, is programmed by the regulated output voltage. The relationship between CT discharge current, IDCHG, and output voltage is illustrated as follows:
3. In this region, a transconductance amplifier reduces
IDCHG in order to maintain VOUT in regulation.
4. If VOUT should rise above its regulation range, IDCHG
falls to zero and the circuit returns to the minimum frequency established by RS and CT.
The range of switching frequencies is established by
RON, ROFF, RS, and CT as follows:
Frequency = 1/(TON + TOFF)
TON = RON • CT • 4.6 V/(VIN - 4.5V)
TOFF (max) = 1.4 • RS • CT
Regions 1 and 4
TOFF = ROFF • CT • 3.7V /(VOUT - 0.7V)
Region 2, excluding the effects of RS
which have a minimal impact on TOFF.
1. When VOUT = 0, the off time is infinite. This feature
provides inherent short circuit protection. However, to
ensure output voltage startup when the output is not a
short, a high value resistor, RS, is placed in parallel
with CT to establish a minimum switching frequency.
The above equations assume that VCC equals 9V. The
voltage at TON increases from approximately 2.5V to
6.5V while CT is charging. To take this into account, VIN
is adjusted by 4.5V in the calculation of TON. The voltage
at TOFF is approximately 0.7V.
2. As VOUT rises above approximately 0.7V to its regulated value, IDCHG is defined by ROFF, and therefore is
equal to:
DESIGN EXAMPLE
The UCC3889 regulates a 12 volt, 1 Watt nonisolated DC output from AC inputs between 80 and 265 volts. In this example, the IC is programmed to deliver a maximum on time gate drive pulse width of 2.4 microseconds which occurs
at 80 VAC. The corresponding switching frequency is approximately 100kHz at low line, and overall efficiency is approximately 50%. Additional design information is available in Unitrode Application Note U-149.
UDG-93062-3
2
UCC1889
UCC2889
UCC3889
ABSOLUTE MAXIMUM RATINGS
CONNECTION DIAGRAM
ICC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA
Current into TON Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5mA
Voltage on VOUT Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20V
Current into TOFF Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250µA
Storage Temperature . . . . . . . . . . . . . . . . . . . . -65°C to +150°C
Note: Unless otherwise indicated, voltages are referenced to
ground and currents are positive into, negative out of, the specified terminals.
DIL-8, SOIC-8 (Top View)
N or J, D Package
ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications hold for TA = 0°C to 70°C for the
UCC3889, -40°C to +85°C for the UCC2889, and -55°C to +125°C for the UCC1889.
No load at DRIVE pin (CLOAD=0).
PARAMETER
General
VCC Zener Voltage
Startup Current
Operating Current I(VOUT)
Under-Voltage-Lockout
Start Threshold
Minimum Operating Voltage after Start
Hysteresis
Oscillator
Amplitude
CT to DRIVE high Propagation Delay
CT to DRIVE low Propagation Delay
Driver
VOL
VOH
Rise Time
Fall Time
Line Voltage Detection
Charge Coefficient: ICHG / I(TON)
Minimum Line Voltage for Fault
Minimum Current I(TON) for Fault
On Time During Fault
Oscillator Restart Delay after Fault
VOUT Error Amp
VOUT Regulated 12V (ADJ Open)
VOUT Regulated 18V (ADJ = 0V)
Discharge Ratio: IDCHG / I(TOFF)
Voltage at TOFF
Regulation gm (Note 1)
TEST CONDITIONS
MIN
TYP
MAX UNITS
ICC < 1.5mA
VOUT = 0
VOUT = 11V, F = 150kHz
8.6
9.0
150
1.2
9.3
250
2.5
V
µA
mA
VOUT = 0
VOUT = 0
VOUT = 0
8.0
6.0
1.8
8.4
6.3
8.8
6.6
V
V
V
VCC = 9V
Overdrive = 0.2V
Overdrive = 0.2V
3.5
3.7
100
50
3.9
200
100
V
ns
ns
0.15
0.7
8.8
7.8
35
30
0.4
1.8
V
V
V
V
ns
ns
0.79
80
220
2
0.85
100
I = 20mA, VCC = 9V
I = 100mA, VCC = 9V
I = −20mA, VCC = 9V
I = −100mA, VCC = 9V
CLOAD = 1nF
CLOAD = 1nF
VCT = 3V, DRIVE = High, I(TON) = 1mA
RON = 330k
RON = 330k
CT = 150pF, VLINE = Min − 1V
8.5
6.1
0.73
60
70
60
0.5
ms
VCC = 9V, IDCHG = I(TOFF)/2
VCC = 9V, IDCHG = I(TOFF)/2
11.2
16.5
11.9
17.5
12.8
19.5
I(TOFF) = 50µA
I(TOFF) = 50µA
Max IDCHG = 50µA
Max IDCHG = 125µA
0.95
0.6
1.01
0.95
1.0
1.7
1.07
1.3
0.8
V
µA
µs
2.9
V
V
V
mA/V
mA/V
∆IDCHG
Note 1: gm is defined as
for the values of VOUT when VOUT is in regulation. The two points used to calculate gm are for
∆VOUT
IDCHG at 65% and 35% of its maximum value.
3
UCC1889
UCC2889
UCC3889
PIN DESCRIPTIONS
resistor connected between VOUT and TOFF.
ADJ: The ADJ pin is used to provide a 12V or an 18V
regulated supply without additional external components.
To select the 12V option, ADJ pin is left open. To select
the 18V option, ADJ pin must be grounded. For other output voltages less than 18V, a resistor divider between
VOUT, ADJ and GND is needed. Note, however, that for
output voltages less than VCC, the device needs additional bootstrapping to VCC from an external source such
as the line voltage. If so, precautions must be taken to
ensure that total ICC does not exceed 5mA.
TON (line voltage control): TON serves three functions.
When CT is discharging (off time), the current through
TON is routed to VCC. When CT is charging (on time), the
current through TON is split 80% to set the CT charge
time and 20% to sense minimum line voltage which occurs for a TON current of 220µA. For a minimum line voltage of 80V, RON is 330kΩ.
The CT voltage slightly affects the value of the charge
current during the on time. During this time, the voltage at
the TON pin increases from approximately 2.5V to 6.5V.
CT (timing capacitor): The signal voltage across CT has
a peak-to-peak swing of 3.7V for 9V VCC. As the voltage
on CT crosses the oscillator upper threshold, DRIVE goes
low. As the voltage on CT crosses the oscillator lower
threshold, DRIVE goes high.
VCC (chip supply voltage): The supply voltage of the
device at pin VCC is internally clamped at 9V. Normally,
VCC is not directly powered from an external voltage
source such as the line voltage. In the event that VCC is
directly connected to a voltage source for additional bootstrapping, precautions must be taken to ensure that total
ICC does not exceed 5mA.
DRIVE: This output is a CMOS stage capable of sinking
200mA peak and sourcing 150mA peak. The output voltage swing is 0 to VCC.
GND (chip ground): All voltages are measured with respect to GND.
VOUT (regulated output): The VOUT pin is directly connected to the power supply output voltage. When VOUT is
greater than VCC, VOUT bootstraps VCC.
TOFF (regulated output control): TOFF sets the discharge current of the timing capacitor through an external
BLOCK DIAGRAM
UDG-93064-2
4
UCC1889
UCC2889
UCC3889
TYPICAL WAVEFORMS
5
UCC1889
UCC2889
UCC3889
UNITRODE INTEGRATED CIRCUITS
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. 603-424-2410 • FAX 603-424-3460
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