UNISONIC TECHNOLOGIES CO., LTD
UC3863
LOW COST POWER-SAVING
MODE PWM CONTROLLER
FOR FLYBACK CONVERTERS
DESCRIPTION
LINEAR INTEGRATED CIRCUIT
The
UC3863
is a high performance current mode PWM
controller ideally suited for low standby power. The PWM switching
frequency is programmable externally at normal operation. Low
V
DD
startup current make the power reliable on startup design and
a large value resistor could be used in the startup circuit to
minimize the standby power. At no load condition, the IC operates
in power-saving mode for lower standby power, decreasing
frequency for Higher conversion efficiency at light load condition.
The
UC3863
contains protection with automatic recovery
including OLP (over load protection), OTP (over temperature
protection), OVP (over voltage protection), UVLO (V
DD
over voltage clamp and under voltage lockout).To protect
the power MOSFET, Gate-drive output is fixed up to 15V max. The
UC3863
contains protection OCP (cycle-by-cycle
current limiting).
The internal slope compensation improves system stability at high PWM duty cycle output. Leading-edge
blanking on current sense input removes the signal glitch, which offering minimal external component count in the
design. Excellent EMI performance is achieved with UTC proprietary frequency hopping technique
(ZL201020615247.1) together with soft driver control. Audio noise is eliminated due to switch frequency more than
20kHz during operation.
The
UC3863
has such applications as: battery charger, power adaptor, set-top box power supplies, ink jet
printers, open-frame SMPS
FEATURES
* Programmable PWM Frequency
* Gate output voltage clamped at 15V
* Low start-up current
* Cycle-by-cycle Current Limiting
* Under voltage lockout (UVLO)
* Few external components required
* UTC proprietary frequency hopping technology for Improved EMI
performance.
* Power-saving mode for high light-load and standby efficiency
* Dynamic peak current limiting for constant output power
* Built-in synchronized slope compensation
* OTP,OLP,OVP and V
DD
clamp for higher security
ORDERING INFORMATION
Ordering Number
Lead Free
Halogen Free
UC3863L-AG6-R
UC3863G-AG6-R
UC3863L-S08-T
UC3863G-S08-T
UC3863L-S08-R
UC3863G-S08-R
xx: Output Voltage, refer to Marking Information.
Package
SOT-26
SOP-8
SOP-8
Packing
Tape Reel
Tube
Tape Reel
Note:
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Copyright © 2013 Unisonic Technologies Co., Ltd
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QW-R103-058, C
UC3863
MARKING INFORMATION(For SOT-26)
LINEAR INTEGRATED CIRCUIT
PIN CONFIGURATION
SOT-26
SOP-8
PIN DESCRIPTION
PIN NAME
GND
FB
RI
SENSE
V
DD
GATE
NC
PIN TYPE
P
I
I
I
P
O
-
DESCRIPTION
Ground.
Feedback input pin. The PWM duty cycle is determined by
voltage level into this pin and SENSE pin input.
A resistor connected between RI and GND sets switching
frequency. A 100kΩ resistor R
I
results in a 65KHz switching
frequency.
Current sense input pin. Connected to MOSFET current sensing
resistor node.
Power supply.
The totem-pole output driver for driving the power MOSFET.
No Connection
PIN NO.
SOT-26
SOP-8
1
8
2
3
4
5
6
-
7
5
4
2
1
3, 6
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QW-R103-058, C
UC3863
BLOCK DIAGRAM
V
DD
5/2
Frequency
Hopping
UVLO
Reference voltage
RI
3/5
Oscillator
LINEAR INTEGRATED CIRCUIT
OVP
Latch
Logic
Control
OTP
FB 2/7
Slope Compensation
Burstmode
S
R
Q
Q
Driver
6/1 GATE
PWM COMP
Constant Power Limit
OCP
LEB
4/4 SENSE
1/8
GND
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QW-R103-058, C
UC3863
PARAMETER
LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATINGS
(T
A
=25°C, V
DD
=15V, unless otherwise specified)
SYMBOL
RATINGS
UNIT
Supply Voltage
V
DD
30
V
Input Voltage to FB Pin
V
FB
-0.3 ~ 7
V
Input Voltage to CS Pin
V
SENSE
-0.3 ~ 7
V
Junction Temperature
T
J
+150
C
Operating Temperature
T
OPR
-40 ~ +125
°C
Storage Temperature
T
STG
-50 ~ +150
C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
OPERATING RANGE
PARAMETER
SYMBOL
V
DD
RATINGS
10 ~ 26
UNIT
V
Supply Voltage
ELECTRICAL CHARACTERISTICS
(T
A
=25°C, V
DD
=15V, R
I
=100KΩ，unless otherwise specified)
SYMBOL
I
STR
I
OP
I
CLAMP
V
THD(ON)
V
DD(MIN)
V
FB-OPEN
A
VCS
V
FB(OUT)
V
FB(END)
V
FB(IN)
F
SW
D
MAX
F
J(SW)
F
DV
F
DT
R
I
R
FB
V
OVP
V
OLP
T
Delay
T
(THR)
V
CS
T
LEB
V
OL
V
OH
t
R
t
F
TEST CONDITIONS
V
DD
= V
DD(ON)
-0.1V
V
FB
=3.5V
V
DD
>V
OVP
13
7.5
MIN
TYP
5
1.5
15
14
MAX
20
5
UNIT
μA
mA
mA
V
V
V
V/V
V
V
V
KHz
KHz
%
%
%
%
KΩ
KΩ
V
V
mS
°C
V
ns
V
V
ns
ns
PARAMETER
SUPPLY SECTION
Start Up Current
IC Operating current
VDD Zener Clamp current
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold Voltage
Min. Operating Voltage
CONTROL SECTION
V
FB
Open Loop Voltage Level
PWM Input Gain
Burst-Mode Out FB Voltage
Reduce-Frequency end FB Voltage
Burst-Mode Enter FB Voltage
Normal
Switch Frequency
Power-Saving
Duty Cycle
Frequency Hopping
Frequency VDD Stability
Frequency Temperature Stability
RI Resistor Value Range
Feedback Resistor
PROTECTION SECTION
VCC Over Voltage Protection Threshold
FB PIN Over Load Protection Threshold
Over Load Protection Delay-Time
OTP threshold
CURRENT LIMITING SECTION
Over Current Flat Threshold Voltage
Lead Edge Blanking Time
DRIVER OUTPUT SECTION
Output Voltage Low State
Output Voltage High State
Output Voltage Rise Time
Output Voltage Fall Time
15
12
∆V
FB
/∆V
CS
V
SENSE
=0
V
SENSE
=0
V
SENSE
=0
V
FB
=3.5V, RI=100KΩ
Before enter burst mode
V
FB
=3.5V, V
SENSE
=0
V
DD
=12V~20V
T=-20~100°C
60
5
3
1.1
1.8
0.9
65
22
75
70
-4
1.5
100
11
26
4.8
55
135
0.65
400
50
+4
5
5
150
V
FB
=4.2V
4.5
V
FB
=4.2V
V
FB
=4.2V
0.6
5.2
0.7
V
DD
=16,I
O
=-20mA
V
DD
=16,I
O
= 20mA
C
L
=1.0nF
C
L
=1.0nF
0.8
11
100
60
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QW-R103-058, C
UC3863
OPERATION DESCRIPTION
LINEAR INTEGRATED CIRCUIT
The
UC3863
devices integrate many useful designs into one controller for low-power switch-mode power
supplies. The following descriptions highlight some of the features of the
UC3863
series.
Start-up Current
The start-up current is only 5μA. Low start-up current allows a start-up resistor with a high resistance and a
low-wattage to supply the start-up power for the controller. For AC/DC adaptor with universal input range design, a
2.5~3MΩ, 1/8W startup resistor could be used together with a V
DD
capacitor to provide a fast startup and low power
dissipation solution.
Power-Saving Mode Operation
The proprietary Power-Saving Mode function provides linearly decreasing the switching frequency under
light-load conditions for higher efficiency. The feedback voltage, which is sampled from the voltage feedback loop, is
taken as the reference. Once the feedback voltage dropped below the threshold voltage, the switching frequency
starts to decrease. This Power-Saving Mode function dramatically reduces power consumption under light-load
conditions. The 22KHz minimum frequency control also eliminates the audio noise at any loading conditions.
At zero load condition, the magnitude of power loss is in proportion to the number of switching events within a
fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the
energy. The
UC3863
enter burst mode at standby condition to minimize the switching loss and reduces the standby
power consumption. Power supplies using the
UC3863
can easily meet even the strictest regulations regarding
standby power consumption.
Switch Frequency Set
The maximum switch frequency is set through the 100KΩ RI-pin resistor to 65KHz. Switch frequency is
modulated by output power P
OUT
during IC operating. At no load or light load condition, most of the power dissipation
in a switching mode power supply is from switching loss on the MOSFET transistor, the core loss of the transformer
and the loss on the snubber circuit. The magnitude of power loss is in proportion to the number of switching events
within a fixed period of time. So lower switch frequency at lower load, which more and more improve IC’s efficiency
at light load. At from no load to light load condition, The IC will operate at from Burst mode to Reducing Frequency
Mode. The relation curve between f
SW
and P
OUT
/P
OUT (MAX)
as followed Fig.1. The maximum switch frequency is set
through the RI-pin resistor RI: F
SW
=6500/RI (KΩ) KHz.
Fig.1 The relation curve between f
SW
and relative output power P
OUT
/ P
OUT (MAX)
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QW-R103-058, C
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