Datasheet

UNISONIC TECHNOLOGIES CO., LTD
USRB01
Preliminary
LINEAR INTEGRATED CIRCUIT
HIGH PRECISION CC/CV
PRIMARY SIDE SWITCH

DESCRIPTION
The UTC USRB01 is a primary controller for 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 USRB01 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 UTC USRB01 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, VDD over voltage
protection, feedback loop open protection, short circuit protection,
leading edge blanking, OTP, VDD under voltage lockout, etc.

FEATURES
* ±5% constant voltage regulation at universal AC input
* Primary side control without TL431 and opto-coupler
* High precision constant current regulation at universal AC
input
* Programmable CV and CC regulation
* Eliminates control loop compensation circuitry
* Flyback topology in DCM operation
* Random frequency modulation to reduce system EMI
* Built-in power NPN

SOP-8
* Programmable cable drop compensation
* Built-in leading edge blanking
* Built-in primary winding inductance compensation
* Open circuit protection
* Output over voltage protection
* VDD over voltage protection
* Short circuit protection
* Over temperature protection
ORDERING INFORMATION
Ordering Number
USRB01G-S08-R
Package
SOP-8
Packing
Tape Reel
USRB01G-S08-R

(1)Packing Type
(1) R: Tape Reel
(2)Package Type
(2) S08: SOP-8
(3)Green Package
(3) G: Halogen Free and Lead Free
MARKING
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USRB01
Preliminary

PIN CONFIGURATION

PIN DESCRIPTION
PIN NO.
1
2
3
4
5~6
7~8

PIN NAME
VCC
VC
FB
CS
C
GND
`
LINEAR INTEGRATED CIRCUIT
DESCRIPTION
Power supply
Low pass filter capacitor for cable compensation
The voltage feedback from the auxiliary winding
Current sense input
The collector of the power NPN
Ground
BLOCK DIAGRAM
VCC 1
I_ drive
Regulator
& Ref
5/6
Por
Base
drive
Logic core
FB 3
+
-
OVP
+
-
CV
controller
Tdemag
detector
+
-
+
-
Drop
comp
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4 CS
LEB
CC
controller
UNISONIC TECHNOLOGIES CO., LTD
C
2
7/8
VC
GND
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
Preliminary
`
LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATING
PARAMETER
SYMBOL
RATINGS
UNIT
VDD Voltage
-0.3~30
V
VC Voltage
-0.3~7
V
C Voltage
-0.3~700
V
CS Input Voltage
-0.3~7
V
FB Input Voltage
-0.3~7
V
Junction Temperature
TJ
-40~150
°C
Storage Temperature
TSTG
-55~150
°C
Lead Temperature (Soldering, 10 secs)
TOPR
260
°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 DATA
PARAMETER
Junction to Ambient

SYMBOL
θJC
RATINGS
150
UNIT
°C/W
ELECTRICAL CHARACTERISTICS (TA=25°C, VDD=15V, if not otherwise noted)
PARAMETER
Supply Voltage (VDD) Section
Start up Current
Static Current
Turn-off Threshold Voltage
Turn-on Threshold Voltage
VDD Over Protect Voltage
Operating Voltage
Current Sense Input Section
LEB Time
Over Current Threshold
OCP Propagation Delay
FB Input Section
Reference Voltage for Feedback
Threshold
Maximum Cable Compensation
Current
Power BJT Section
Collector-emitter breakdown voltage
Collect Peak Current
Collector-Base Breakdown Voltage
On Chip Over Temperature Section
Over Temperature Protection
SYMBOL
IST
IOP
TEST CONDITIONS
TLEB
VCS
MAX UNIT
6.0
11.5
25
1
300
6.8
12.5
27
3
400
7.6
13.5
29
25
μA
μA
V
V
V
V
470
2.5
500
520
μS
mV
From OCP Comparator to Base
Drive
200
nS
VFB
1.98
2.00
2.02
V
Icable
47
52
56
μA
VCEO
IC
VCBO
IC=10mA, IB=0
IC=10mA
T_otp
UNISONIC TECHNOLOGIES CO., LTD
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TYP
VDD=11V
VDD=15V
VTH(OFF)
VTH (ON)
VDD_OVP
TD_OC
MIN
450
0.6
V
A
V
150
°C
700
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
Preliminary
`
LINEAR INTEGRATED CIRCUIT
OPERATION DESCRIPTION
The UTC USRB01 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 VDD pin of UTC USRB01 is connected to the line input through a resistor. A large value startup resistor can be
used to minimize the power loss in application because the start current of UTC USRB01 is very low. When the VDD
voltage reaches VTH (ON), the internal startup circuit is disabled and the IC turns on.
Operating Current
The Operating current of UTC USRB01 is as low as 400μA. 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
USRB01 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.
Figure 2. 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 2V 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.
Constant Current Operation
When the sampled voltage is below 2V reference voltage and the error amplifier output reaches its maximum, thus
UTC USRB01 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.
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
Preliminary
`
LINEAR INTEGRATED CIRCUIT
OPERATION DESCRIPTION (Cont.)
Large
Rcs
Vout
Small
Rcs
Iout
Figure3. Adjustable output power by changing Rcs
Figure4. Secondary current waveform
In CC operation, the CC loop control function of UTC USRB01 will keep a fixed proportion between secondary
inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is
Tdemag 1
(2)
=
TSW
2
Thus the output current is given by:
Iout =
Tdemag 1 NP
1 NP
×
× IPK ×
= ×
×I
2 NS
TSW
4 NS PK
(3)
Programmable Cable drop Compensation
UTC USRB01 has a built-in cable voltage drop compensation to achieve good load regulation. An offset voltage is
generated at FB pin by an internal current flowing into the resistor divider. The current is inversely proportional to the
voltage of VC pin. As a result, it is inversely proportional to the output load current. The voltage drop across the
cable is compensated by this offset voltage at FB pin. It can also be programmed by adjusting the resistance of the
divider to compensate the drop for various cable lines used.
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC USRB01. 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.
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USRB01

Preliminary
`
LINEAR INTEGRATED CIRCUIT
OPERATION DESCRIPTION (Cont.)
Drive BJT
The driver is a push pull stage with the supply voltage VDD. It provides the driving current for the external power
bipolar transistor. The output signal is current-limited to IOUT(SOURCE).
Protection Control
Good power supply system reliability is achieved with its comprehensive protection features including VDD over
voltage protection, OTP, feedback loop open protection, Cycle-by-cycle current limiting, short circuit protection,
leading edge blanking and UVLO, etc.
VDD is supplied by transformer auxiliary winding output. The output of UTC USRB01 is shutdown when VDD drops
below VTH(OFF) and the power converter enters power on start-up sequence thereafter.
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www.unisonic.com.tw
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USRB01

Preliminary
`
LINEAR INTEGRATED CIRCUIT
TYPICAL APPLICATION CIRCUIT
L
Is
Vo
D1
N
NS
NP
FB
VCC
Co
NA
C
UTC USRB01
VC
GND
CS
Rcs
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.
UNISONIC TECHNOLOGIES CO., LTD
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