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BL8835A
QR/PSR CV/CC Controller
GENERAL DESCRIPTION
FEATURES
BL8835A is a high performance, highly integrated
QR (Quasi Resonant Mode) and Primary Side
Regulation (PSR) controller for offline small power
converter applications.
BL8835A has proprietary QR/PSR control for high
efficiency and low EMI. The IC also has built-in
cable drop compensation function, which can
provide excellent CV performance.
BL8835A integrates functions and protections of
Under Voltage Lockout (UVLO), VDD Over Voltage
Protection (VDD OVP), Output Over Voltage
Protection (Output OVP), Soft Start, Cycle-by-cycle
Current Limiting (OCP), Pin Floating Protection,
VDD Clamping.
◆ Proprietary QR/PSR (Quasi-Resonant & Primary
Side Regulation) Control for High Efficiency and
Low EMI
◆ Less than 100mW Standby Power
◆ ±5% CC and CV Precision
◆ Proprietary Cable Drop Compensation
◆ Cycle-by-Cycle Current Limiting
◆ Built-in Leading Edge Blanking (LEB)
◆ Pin Floating Protection
◆ Built-in Soft Start
◆ Output Over Voltage Protection
◆ VDD OVP & Clamp
◆ VDD Under Voltage Lockout (UVLO)
BL8835A is offered in SOP8 package.
APPLICATIONS
Low Power AC/DC offline SMPS for
■ Cell Phone Charger
■ Digital Cameras Charger
■ Small Power Adapter
■ Auxiliary Power for PC, TV etc.
■ Linear Regulator/RCC Replacement
TYPICAL APPLICATION
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BL8835A
QR/PSR CV/CC Controller
GENERAL INFORMATION
Pin Configuration
The pin map is shown as below for SOP8.
VDD
1
8
GND
COMP
2
7
GND
INV
3
6
DRAIN
CS
4
5
DRAIN
Package Dissipation Rating
Package
SOP8
RθJA (℃/W)
145
Absolute Maximum Ratings
Parameter
Value
Drain Voltage (off state) -0.3V to Bvdss
-0.3 to
VDD Voltage
VDD_clamp
VDD Zener Clamp
10mA
Continuous Current
COMP Voltage
-0.3 to 7V
CS input Voltage
-0.3 to 7V
INV input Voltage
-0.3 to 7V
Max Operation Junction
150℃
Temperature Tj
Min/Max storage
-55 to 150℃
Temperature T-stg
Lead Temperature
260℃
(Soldering,10secs)
TERMINAL ASSIGNMENTS
Pin Num
1
2
Pin Name
VDD
COMP
I/O
P
I
3
INV
I
4
CS
I
5/6
DRAIN
O
7/8
GND
P
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Description
Power Supply
Loop Compensation for CV Stability
The Voltage feedback from auxiliary winding. Connected to resistor
divider from auxiliary winding reflecting output voltage. PWM duty cycle
is determined by EA output and current sense signal at pin 4.
Current sense input
HV MOSFET Drain pin. The Drain pin is connected to the primary lead of
the transformer
Ground
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BL8835A
QR/PSR CV/CC Controller
OUTPUT POWER TABLE
Product
BL8835A
Universal Voltage
Adapter
7.5W
Package
Test Condition
SOP8
Indoor temperature 40℃
BLOCK DIAGRAM
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BL8835A
QR/PSR CV/CC Controller
ELECTRICAL CHARACTERISTICS
(TA=25℃,VDD=16V,if not otherwise noted)
Symbol
Parameter
Supply Voltage (VDD)
I_Startup
VDD Startup Current
I_VDD_Op
Operation Current
Test Conditions
VDD Under Voltage Lockout Exit
(Startup)
UVLO(OFF)
VDD Under Voltage Lockout Enter
VDD Over Voltage Protection trigger
VDD_OVP
VDD_Clamp
VDD Zener Clamp Voltage
Feedback Input Section(INV Pin)
Internal Error Amplifier(EA) reference
VINV_EA_Ref
input
Output over voltage protection thresh
VINV_OVP
old
VINV_Short
Output Short Circuit Threshold
Output Short Circuit Frequency
FClamp_Short
Clamp
Demagnetization comparator
VINV_DEM
threshold
Tmin_OFF
Minimum OFF time
Tmax_OFF
Maximum OFF time
Max Cable compensation current
ICable_max
Current Sense Input Section (CS Pin)
CS Input Leading Edge Blanking Tim
T_blanking
e
Over Current Detection and Control
TD_OC
Delay
Constant Current Section (COMP Pin)
V_comp_ref
Internal CC reference
Power MOSFET Section
I(VDD)=7mA
Max
Unit
2
20
uA
1
1.5
mA
13.0
14.0
15.0
V
8.0
30
32
9.0
32
34
10.0
34
36
V
V
V
1.98
2.0
2.02
V
CL=1nF at GATE
490
2.4
V
0.65
V
50
KHz
75
mV
2
2.8
40
us
ms
uA
500
ns
100
ns
500
510
610
BVdss
Static, Id=0.4A
Rdson
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Typ.
VDD=UVLO(ON)-1V
, Measure current
into VDD
VINV=1V,CL=0.5nF,
VDD=20V
UVLO(ON)
MOSFET Drain
Source
Breakdown
Voltage
ON Resistance
Min
4/7
mV
V
5.2
6.5
Ω
V1.0
BL8835A
QR/PSR CV/CC Controller
OPERATION DESCRIPTION
BL8835A is a high performance, multimode
controlled, highly integrated QR (Quasi Resonant)
Primary Side Regulation (PSR) controller. The
built-in high precision CV/CC control with high level
protection features make it very suitable for offline
small power converter applications.
◆ Startup Current and Startup Control
Startup current of BL8835A is designed to be very
low (typically 2uA) so that VDD could be charged up
above UVLO(ON) threshold level and device starts
up quickly. A large value startup resistor can
therefore be used to minimize the power loss yet
reliable startup in application.
◆ Operating Current
The operating current in BL8835A is as small as
0.65mA (typical). The small operating current
results in higher efficiency and reduces the VDD
hold-up capacitance requirement.
◆ QR/PSR Control
BL8835A uses a proprietary QR/PSR control for
high efficiency and low EMI. The IC works in
Quasi-Resonant (QR) mode in Constant Current
(CC) and Constant Voltage (CV) mode. In this way,
the efficiency is boosted and the EMI is reduced
greatly. The IC can easily meet EPS level 6
standard.
◆ Constant Current (CC) Regulation
I CC (mA) 
N 500(mV )

2 RCS ()
In the equation above,
N---- The turn ratio of primary side winding to
secondary side winding.
Rcs---- The sensing resistor connected between the
Source to GND.
◆ Precision CV/CC Performance
In BL8835A, the parameters are trimmed to tight
range, which makes the system CC/CV to have less
than 5% variation.
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◆ Soft Start
BL8835A features an internal soft start that slowly
increases the threshold of cycle-by-cycle current
limiting comparator during startup sequence. It
reduces the stress on the secondary diode during
startup. Every startup process is followed by a soft
start activation.
◆ Proprietary
Cable
Voltage
Drop
Compensation in CV Mode
When it comes to cellular phone charger
applications, the battery is located at the end of
cable, which causes typically several percentage of
voltage drop on the actual battery voltage. BL8835A
has a proprietary built-in cable voltage drop
compensation block which can provide a constant
output voltage at the end of the cable over the entire
load range in CV mode.
◆ Leading Edge Blanking (LEB)
Each time the power MOSFET is switched on, a
turn-on spike occurs across the sensing resistor. To
avoid premature termination of the switching pulse,
an internal leading edge blanking circuit is built in.
During this blanking period (500ns, typical), the
cycle-by-cycle current limiting comparator is
disabled and cannot switch off the gate driver. Thus,
external RC filter with a small time constant is
enough for current sensing.
◆ Minimum and Maximum OFF Time
In BL8835A, a minimum OFF time (typically 2us) is
implemented to suppress ringing when GATE is off.
The minimum OFF time is necessary in applications
where the transformer has a large leakage
inductance, particularly at low output voltages or
startup. The maximum OFF time in BL8835A is
typically 2.8ms, which provides a large range for
frequency reduction. In this way, a low standby
power of 100mW can be achieved.
◆ Output OVP(Over Voltage Protection) and
Output UVP (Under Voltage Protection)
In BL8835A, the output OVP is integrated by
plateau sampling the auxiliary winding in flyback
phase. The threshold voltage for output OVP is 2.4V,
as shown in Fig.1 Output OVP is auto-recovery
mode protection (mentioned below).
In BL8835A, when sensed INV voltage is below
0.65V, the IC will enter into Under Voltage
Protection (UVP) mode, in which the switching
frequency is clamped, as shown in Fig.1
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BL8835A
QR/PSR CV/CC Controller
◆ Pin Floating Protection
In BL8835A, if pin floating situation occurs, the IC is
designed to have no damage to system.
◆ Soft Gate Drive
BL8835A has a soft totem-pole gate driver with
optimized EMI performance. An internal 16V clamp
is added for MOSFET gate protection at higher than
expected VDD input.
◆ Gate Drive
The internal power MOSFET in BL8835A is driven by
a dedicated gate driver for power switch control. Too
weak the gate drives strength results in higher
conduction and switch loss of MOSFET while too
strong gate drive compromises EMI. A good tradeoff is
achieved through the built-in totem pole gate design
with right output strength control.
Fig.1
◆ Programmable Cable drop Compensation
Fig.1
◆Frequency Clamping @ Output Short Circuit
In BL8835A, when INV voltage is below 0.65V, the
IC will enter into Under Voltage Protection (UVP)
mode, the switching frequency is fixed to 50KHz
(typical). This protection is useful for LED short
circuit protection. When output is short, the
frequency clamping can lower power MOSFET Vds
spike and the system reliability can be improved.
In BL8835A, when output short circuit occurs, the IC
will fix the switching frequency to 50KHz. In this way,
the power MOSFET Vds spike voltage is
suppressed greatly.
◆VDD OVP(Over Voltage Protection)
VDD OVP (Over Voltage Protection) is implemented
in BL8835A and it is a protection of auto-recovery
mode.
◆Auto Recovery Mode Protection
Once a fault condition is detected, switching will
stop. This will cause VDD to fall because no power
is delivered form the auxiliary winding. When VDD
falls to UVLO(off) (typical 9.0V), the protection is
reset and the operating current reduces to the
startup current, which causes VDD to rise. However,
if the fault still exists, the system will experience the
above mentioned process. If the fault has gone, the
system resumes normal operation. In this manner,
the auto restart can alternatively enable and disable
the switching until the fault condition is disappeared.
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In BL8835A, cable drop compensation is implemented
to achieve good load regulation. An offset voltage is
generated at INV by an internal current flowing into the
resister divider. The current is inversely proportional to
the voltage across pin COMP, as a result, it is
inversely proportional to the output load current, thus
the drop due to the cable loss can be compensated.
As the load current decreases from full-load to no load,
the offset voltage at INV will increase. It can also be
programmed by adjusting the resistance of the divider
to compensate the drop for various cable lines used.
◆Protection Control
Good power supply system reliability is achieved with
its rich protection features including Cycle-by-Cycle
current limiting (OCP), VDD clamp, Power on Soft
Start, and Under Voltage Lockout on VDD (UVLO).
VDD is supplied by transformer auxiliary winding
output. The output of BL8835A is shut down when
VDD drops below UVLO (ON) limit and Switcher
enters power on start-up sequence thereafter.
V1.0
BL8835A
QR/PSR CV/CC Controller
PACKAGE MECHANICAL DATA
SOP8 PACKAGE OUTLINE DIMENSIONS
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
1.350
1.750
0.053
0.069
A1
0.050
0.250
0.002
0.010
A2
1.250
1.650
0.049
0.065
B
0.310
0.510
0.012
0.020
C
0.170
0.250
0.006
0.010
D
4.700
5.150
0.185
0.203
E
3.800
4.000
0.150
0.157
E1
5.800
6.200
0.228
0.244
e
1.270(BSC)
0.05(BSC)
L
0.400
1.270
0.016
0.050
θ
0°
8°
0°
8°
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