Datasheet

UNISONIC TECHNOLOGIES CO., LTD
UC1108
Preliminary
CMOS IC
LOW-POWER OFF-LINE
PRIMARY SIDE REGULATION
CONTROLLER

DESCRIPTION
The UTC UC1108 is a primary control unit for switch mode charger
and adapter applications. The controlled variable is transferred by an
auxiliary winding from the secondary to the primary side. The device
uses Pulse Frequency Modulation (PFM) method to build
discontinuous conduction mode (DCM) flyback power supplies.
The UTC UC1108 operates in primary-side sensing and regulation.
Opto-coupler and TL431 could be eliminated. It also eliminates the
need of loop compensation circuitry while maintaining stability. The
UC1108 achieves excellent regulation and high average efficiency, yet
meets the requirement for no-load consumption less than 30mW.
The UTC UC1108 has the built-in programmable cable voltage
drop compensation function, which make it flexible to accommodate
various cables with different gauges and lengths
The UTC UC1108 achieves high precision CV/CC regulation and
high power efficiency. It offers comprehensive protection coverage
with auto-recovery features including Cycle-by-cycle current limiting,
output over voltage protection, feedback loop open protection, short
circuit protection, leading edge blanking, VCC under voltage lockout,
etc.

SOP-8
FEATURES
* 30mW No-load Input Power
* Primary side control for eliminating opto-coupler and secondary
CV/CC control circuitry
* Proprietary CC tightening technique to achieve vertical CC profile
* Programmable output cable voltage drop compensation
* Compensation for external component temperature variations
* Random frequency adjustment to reduce system EMI
* Flyback topology in DCM operation
* Built-in soft start
* Over voltage protection
* Short circuit protection

ORDERING INFORMATION
Ordering Number
UC1108G-S08-R
UC1108G-S08-R
Package
SOP-8
(1)Packing Type
(1) R: Tape Reel
(2)Package Type
(2) S08: SOP-8
(3)Green Package
(3) G: Halogen Free and Lead Free
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Copyright © 2015 Unisonic Technologies Co., Ltd
Packing
Tape Reel
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UC1108
Preliminary

MARKING

PIN CONFIGURATION

PIN DESCRIPTION
PIN NO.
1
2
3
4
5
6
7
8

PIN NAME
CS
VCC
OUT
GND
CPC
FB
CPR
BIAS
CMOS IC
DESCRIPTION
The primary current sense
Supply voltage
This pin drives the base of external power NPN switch
Ground
This pin connects a capacitor for output cable compensation
The voltage feedback from the auxiliary winding
Connects a resistor to FB pin for adjustable output cable compensation
This pin sets the bias current inside UC1108 with an external resistor to GND
BLOCK DIAGRAM
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UC1108

Preliminary
CMOS IC
ABSOLUTE MAXIMUM RATING
PARAMETER
SYMBOL
RATINGS
UNIT
Voltage at VCC Pin to GND
-0.3~36
V
Voltage at CS, OUT to GND
-0.3~7
V
FB Input
-40~10
V
Output Current at OUT
Internally limited
A
Operating Junction Temperature
TOPR
150
°C
Storage Temperature
TSTG
-65~150
°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.

THERMAL RESISTANCES CHARACTERISTICS
PARAMETER
Junction to Ambient

SYMBOL
θJA
RATING
190
UNIT
°C/W
ELECTRICAL CHARACTERISTICS (VCC=15V, TA=25°C, unless otherwise specified.)
PARAMETER
UVLO SECTION
Start-Up Threshold
Minimal Operating Voltage
Reference Voltage
BIAS Pin Voltage
STANDBY CURRENT SECTION
Start-Up Current
SYMBOL
TEST CONDITIONS
VTH (ST)
VOPR(min)
VBIAS
IST
RBIAS=200kΩ, After Turn On
TYP
MAX
UNIT
17
8.2
18.5
9.2
21
10.2
V
V
1.0
1.1
1.2
V
0.6
µA
390
480
µA
28
36
44
mA
490
390
513
413
500
535
435
mV
mV
ns
1.8
3.97
-2.0
2.4
4.03
-1.7
3.0
4.09
-1.4
µA
V
V
3.5
200
V
µA
9
V
VCC=VTH (ST)-0.5V,
RBIAS=200kΩ,Before Start-Up
RBIAS=200kΩ
Operating Current
ICC(OPR)
DRIVE OUTPUT SECTION
OUT Maximum Current Source
IOUT
RBIAS=200kΩ
CURRENT SENSE SECTION
Current Sense Threshold
VCS
Pre-Current Sense
VCS(PRE)
Leading Edge Blanking
FEEDBACK INPUT SECTION
Feedback Pin Input Leakage Current
IFB
VFB=4V
Feedback Threshold
VFB
Enable Turn-on Voltage
VFB(EN)
OUTPUT VOLTAGE COMPENSATION SECTION
CPR Voltage
VCPR Dons (Tons/T): From 55% to 0.02%
CPR Sink Current
ICPR
PROTECTION SECTION
Over Voltage Protection
VFB(OVP)
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MIN
1.5
7
8
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UC1108

Preliminary
CMOS IC
OPERATION DESCRIPTION
The UTC UC1108 is a primary control unit for switch mode charger and adapter applications. It operates in
primary-side sensing and regulation. Opto-coupler and TL431 could be eliminated. Proprietary built-in CV and CC
control can achieve high precision CV/CC performance. It uses Pulse Frequency Modulation (PFM) method to build
discontinuous conduction mode (DCM) flyback power supplies.
Startup control
The voltage regulator provides the internal power supply VDD. For VCC and VDD external capacitors are required.
The current biasing of UTC UC1108 is adjustable by an external resistor. Internal time constants, thresholds and the
output current depend from the value of this resistor. The startup circuit activates the IC after startup and deactivates
the IC in case of UVLO.
Operating Current
The Operating current of UTC UC1108 is as low as 400uA. Good efficiency and very low standby power can be
achieved.
Constant Voltage Operation
The output voltage is defined by the transmission ratio between the secondary and auxiliary winding. The UTC
UC1108 captures the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV) mode to
regulate the output voltage. The auxiliary voltage reflects the output voltage is given by:
N
VAUX = A × ( VO + ∆V )
(1)
NS
Where△V indicates the drop voltage of the output diode.
Figure2. Auxiliary voltage waveform
Via a resistor divider connected between the auxiliary winding and FB, the VAUX is sampled at the Tsampling end
and it is hold until the next sampling. The sampled voltage is compared with 4V reference voltage and the error is
amplified. The error amplifier output reflects the load condition and controls the Toff time to regulate the output
voltage, thus constant output voltage can be achieved.
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UC1108

Preliminary
CMOS IC
OPERATION DESCRIPTION (Cont.)
Constant Current Operation
When the sampled voltage is below 4V reference voltage and the error amplifier output reaches its maximum,
thus UTC UC1108 operates in constant-current (CC) mode. The CC point and maximum output power can be
externally adjusted by external current sense resistor Rcs. The larger Rcs, the smaller CC point is, and the smaller
output power becomes.
Figure3. Adjustable output power by changing Rcs
Figure4. Secondary current waveform
In CC operation, the CC loop control function of UTC UC1108 will keep a fixed proportion between secondary
inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is
Tdemag 4
=
Tsw
7
(2)
Thus the output current is given by:
Iout =
1 NP
Tdemag 2 NP
×
× Ipk ×
= ×
× Ipk
2 NS
Tsw
7 NS
(3)
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC UC1108. The switch current is detected by a sense resistor into
the CS pin. When the power switch is turned on, a turn-on spike will occur on this resistor. A 500ns leading-edge
blanking is built in to avoid false-termination of the switching pulse so that the external RC filtering is no longer
needed.
Drive BJT
The driver is a push pull stage with the supply voltage VCC. It provides the driving current for the external power
bipolar transistor. The output signal is current-limited to IOUT(SOURCE).
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UC1108

Preliminary
CMOS IC
OPERATION DESCRIPTION (Cont.)
Output Cable Compensation
The UTC UC1108 senses the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV)
mode to regulate the output voltage. In CV mode, FB pin voltage VFB is a constant of 4.0V. The CPR pin voltage
VCPR is generated by the internal circuit of UTC UC1108. It linearly decreases with the rise of the output load directly.
Where Dons is the duty cycle of secondary diode, and is equal to Tdemag/Tsw, which is directly proportional to the
output loading. The maximum Dtdemag is 4/7 and the minimal Dtdemag is close to zero in CV mode of UTC
UC1108.
Protection Control
Good power supply system reliability is achieved with its comprehensive protection features including output
over-voltage protection, feedback loop open protection, Cycle-by-cycle current limiting, short circuit protection,
leading edge blanking and UVLO, etc.
VCC is supplied by transformer auxiliary winding output. The output of UTC UC1108 is shutdown when VCC drops
below VTH(OFF) and the power converter enters power on start-up sequence thereafter.
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UC1108

Preliminary
CMOS IC
TYPICAL APPLICATION CIRCUIT (5V/1A)
BOM
Reference
BD1
L1
C1
C2
C3
C4
C5
C6
D1,D2
D3
R1
Component
BD 1A/600V
Inductor, com-choke
EC 4.7u F 400V 105°C
EC 4.7u F 400V 105°C
CC 2.2u F 50V 105°C
CC 0.47u F 50V 0805
CC 1n F 1000V 1206
EC 1000u F 10V 105°C
Diode UTC 1N4007
Diode UTC SB340
R 2.4KΩ 1206 ±5%
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Reference
R2
R3
R4
R5
R6
R7
R8
R9
T1
F1
Q1
Component
R 6.8MΩ 1206 ±5%
R 6.8MΩ 1206 ±5%
R 30KΩ 0805 ±1%
R 9.1KΩ 0805 ±1%
R 27KΩ 0805 ±5%
R 200KΩ 0805 ±5%
R 1.0Ω 1206 ±5%
R 200KΩ 1206 ±5%
EE-16
FUSE 1A 250VAC
NPN Transistor UTC MJE13003
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UC1108
Preliminary
CMOS IC
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
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