Dialog IW1812-20 Off-line digital green-mode pwm controller integrated with power bjt and otp Datasheet

iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
1 Description
The iW1812 is a high performance AC/DC power supply control device which uses digital control technology to build
peak current mode PWM flyback power supplies. This device includes an internal power BJT and operates in quasiresonant mode to provide high efficiency along with a number of key built-in protection features while minimizing the
external component count, simplifying EMI design, and lowering the total bill of material cost. The iW1812 removes the
need for secondary feedback circuitry while achieving excellent line and load regulation. It also eliminates the need for
loop compensation components while maintaining stability in all operating conditions. The pulse-by-pulse waveform
analysis allows for a loop response that is much faster than traditional solutions, resulting in improved dynamic load
response for both one-time and repetitive load transients. The built-in power limit function enables optimized transformer
design in universal off-line applications and allows for a wide input voltage range.
Dialog’s innovative proprietary technology ensures that power supplies built with the iW1812 can achieve both highest
average efficiency and less than 30mW no-load power consumption in a compact form factor.
2 Features
●● Primary-side feedback eliminates opto-isolators and
simplifies design
●● Internal 800V bipolar junction transistor (BJT)
●● No-load power consumption < 30mW at 230VAC with
typical application circuit
●● Adaptive multi-mode PWM/PFM control improving
efficiency
●● Quasi-resonant operation for highest overall
efficiency
●● Ultra-low start-up current (1.7μA typical)
●● Dynamic BJT base drive current control
●● Very tight constant voltage and constant current
regulation with primary-side-only feedback
●● 64kHz PWM switching frequency
●● Fast dynamic load response for both one-time and
repetitive load transients
●● EZ-EMI® design to easily meet global EMI standards
●● No external compensation components required
●● Complies with EPA 2.0 energy-efficiency
specifications with ample margin
●● Built-in soft start
●● Built-in short-circuit protection and output over-voltage
protection
●● Built-in current-sense-resistor short-circuit protection
●● Built-in over-temperature protection (OTP)
●● No audible noise over entire operating range
3 Applications
●● Low-power AC/DC power supply for smart meters,
motor control, industrial, and home appliances
applications
●● Linear AC/DC replacement
Datasheet
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© 2016 Dialog Semiconductor
iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
L
VOUT
+
+
GND
N
U1
iW1812
1
C
E
8
2
C
ISENSE
7
VSENSE
6
GND
5
4
VCC
Figure 3.1 : iW1812 Typical Application Circuit
WARNING:
The iW1812 is intended for high voltage AC/DC offline applications. Contact with live high voltage offline
circuits or improper use of components may cause lethal or life threatening injuries or property damage. Only
qualified professionals with safety training and proper precaution should operate with high voltage offline
circuits.
iW1812 Output Power Table at Universal Input (85VAC–264VAC)
Condition
Adapter1
Open Frame2
Output Power (W)
4.0
5.0
Note 1: Maximum practical continuous output power measured at enclosure internal ambient temperature of 60°C and device emitter
pin (pin 8) temperature of ≤ 90°C (adapter is placed in a non-ventilated environment).
Note 2: Maximum practical continuous output power measured at open frame ambient temperature of 50°C and device emitter pin
(pin 8) temperature of ≤ 90°C while minimum bulk capacitor voltage is kept above 90V and no special heatsinking is used
(test unit is placed in a non-ventilated environment).
Note 3: The output power can vary depending on the power supply system designs and operating conditions. See Section 10.14 for
more details.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
4 Pinout Description
iW1812
1
C
E
8
2
C
ISENSE
7
VSENSE
6
GND
5
4
VCC
Figure 4.1 : 7-Lead SOIC Package
Pin Number
Pin Name
1
C
BJT Collector Collector of internal bipolar junction transistor (BJT).
2
C
BJT Collector Collector of internal BJT.
4
VCC
Power Input
5
GND
Ground
6
VSENSE
Analog Input Auxiliary voltage sense (used for primary-side regulation).
7
ISENSE
Analog Input
Primary current sense. Used for cycle-by-cycle peak current control
and current limit.
8
E
BJT Emitter
Emitter of internal BJT (pin 7 and pin 8 must be shorted externally on
the PCB).
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Type
Pin Description
Power supply for control logic.
Ground.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
5 Absolute Maximum Ratings
Absolute maximum ratings are the parameter values or ranges which can cause permanent damage if exceeded.
For maximum safe operating conditions, refer to Electrical Characteristics in Section 7. (TA = 25°C, unless otherwise
noted). Proper design precautions must be made to ensure that the internal die junction temperature of the iW1812
does not exceed 150°C. Otherwise permanent damage to the device may occur.
Parameter
Symbol
Value
Units
DC supply voltage range (pin 4, ICC = 20mA max)
VCC
-0.3 to 18
V
Continuous DC supply current at VCC pin (VCC = 15V)
ICC
20
mA
VSENSE input (pin 6, IVsense ≤ 10mA)
-0.7 to 4.0
V
ISENSE input (pin 7)
-0.3 to 4.0
V
±2,000
V
±100
mA
VCES
800
V
Collector current1
IC
1.5
A
Collector peak current1 (tp < 1ms)
ICM
3
A
Maximum junction temperature
TJ MAX
150
°C
Storage temperature
TSTG
–55 to 150
°C
Lead temperature during IR reflow for ≤ 15 seconds
TLEAD
260
°C
Symbol
Value
Units
θJA
132
°C/W
ψJB
71
°C/W
ψJ-BJT
49
°C/W
TSD
150
°C
TSD-R
100
°C
ESD rating per JEDEC JESD22-A114
Latch-up test per JESD78A
Collector-Emitter breakdown voltage
(Emitter and base shorted together; IC = 1mA, REB = 0Ω)
Note 1: Limited by maximum junction temperature.
6 Thermal Characteristics
Parameter
Thermal Resistance Junction-to-Ambient1
Thermal Resistance Junction-to-GND pin (pin 5)
2
Thermal Resistance Junction-to-Collector pin (pin 1) 2
Thermal Shutdown Threshold
3
Thermal Shutdown Recovery 3
Note 1: θJA is measured in a one-cubic-foot natural convection chamber.
Note 2: ψJB [Psi Junction to Board] provides an estimation of the die junction temperature relative to the PCB [Board] surface
temperature. ψJ-BJT [Psi Junction to Collector pin] provides an estimation of the die junction temperature relative to the
collector pin [internal BJT Collector] surface temperature. ψJB is measured at the ground pin (pin 5) without using any thermal
adhesives. See Section 10.14 for more information.
Note 3: These parameters are typical and they are guaranteed by design.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
7 Electrical Characteristics
VCC = 12V, -40°C ≤ TA ≤ 85°C, unless otherwise specified
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
1
μA
1.548
V
VSENSE SECTION (Pin 6)
IBVS
VSENSE = 2V
Nominal voltage threshold
VSENSE(NOM)
TA = 25°C, negative edge
Output OVP threshold
VSENSE(MAX)
TA = 25°C, negative edge
Input leakage current
1.518
1.533
1.834
V
ISENSE SECTION (Pin 7)
Over-current threshold
VOCP
1.11
1.15
1.19
V
ISENSE regulation upper limit1
VIPK(HIGH)
1.0
V
ISENSE regulation lower limit1
VIPK(LOW)
0.23
V
Input leakage current
ILK
ISENSE = 1.0V
1
μA
16
V
VCC SECTION (Pin 4)
Maximum operating voltage1
VCC(MAX)
Start-up threshold
VCC(ST)
VCC rising
10.0
11.0
12.0
V
Under-voltage lockout threshold
VCC(UVL)
VCC falling
3.8
4.0
4.2
V
Start-up current
IIN(ST)
VCC = 10V
1.0
1.7
3.0
μA
Quiescent current
ICCQ
No IB current
2.7
4.0
mA
Zener breakdown voltage
VZB
Zener current = 5mA
TA=25°C
19.5
20.5
V
ICB0
VCB = 800V, IE = 0A
0.01
mA
VCE = 800V, REB = 0Ω,
TA = 25°C
0.01
VCE = 800V, REB = 0Ω,
TA = 100°C
0.02
VCE = 500V, REB = 0Ω,
TA = 25°C
0.005
18.5
BJT Section (Pin 1, Pin 2, and Pin 8)
Collector cutoff current
Collector-Emitter cutoff current
DC Current Gain2
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hFE
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VCE = 5V, IC = 0.2A
15
40
VCE = 5V, IC = 0.3A
10
30
VCE = 5V, IC = 1mA
10
mA
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
7 Electrical Characteristics (cont.)
VCC = 12V, -40°C ≤ TA ≤ 85°C, unless otherwise specified
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Collector-Base breakdown voltage
VCB0
IC = 0.1mA
800
V
Collector-Emitter breakdown voltage
(Emitter and base shorted together)
VCES
IC = 1mA, REB = 0Ω
800
V
VCEO(SUS)
IC = 1mA, LM = 25mH
500
V
VCE(SAT)
IC = 0.1A, IB = 0.02A
0.1
fSW
> 50% load
64
BJT Section (Pin 1, Pin 2, and Pin 8)
Collector-Emitter sustain voltage
Collector-Emitter saturation voltage2
PWM switching frequency3
0.3
V
kHz
Note 1: These parameters are not 100% tested and guaranteed by design and characterization.
Note 2: Impulse tP ≤ 300μs, duty cycle ≤ 2%.
Note 3: Operating frequency varies based on the load conditions, see Section 10.6 for more details.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
8 Typical Performance Characteristics
4.58
VCC Start-up Threshold (V)
12.0
VCC UVLO (V)
4.54
4.50
4.46
4.42
4.38
-50
-25
0
25
50
75
100
Ambient Temperature (ºC)
125
10.4
-25
0
25
50
75
100
Ambient Temperature (ºC)
125
150
2.010
Internal Reference Voltage (V)
fsw @ Load > 50% (kHz)
10.8
Figure 8.2 : Start-up Threshold vs. Temperature
70
67
64
61
58
-25
0
25
50
75
100
Ambient Temperature (ºC)
125
150
Figure 8.3 : Switching Frequency vs. Temperature1
VCC Supply Start-up Current (µA)
11.2
10.0
-50
150
Figure 8.1 : VCC UVLO vs. Temperature
55
-50
11.6
2.006
2.002
1.998
1.994
1.990
-50
-25
0
25
50
75
100
Ambient Temperature (ºC)
125
150
Figure 8.4 : Internal Reference vs. Temperature
2.5
2.0
1.5
1.0
0.5
0.0
0.0
3.0
6.0
VCC (V)
9.0
12.0
Figure 8.5 : VCC Supply Start-up Current vs. VCC
Note: Operating frequency varies based on the load conditions, see Section 10.6 for more details.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
9 Functional Block Diagram
4 VCC
Start-up
ENABLE
VSENSE 6
VFB
Signal
Conditioning
Digital
Logic
Control
Thermal
Shutdown
OCP
GND
VSENSE(NOM)
= 1.533V
5
DAC
BJT
Base
Drive
1
C (collector)
2
C (collector)
8
E (emitter)
7
ISENSE
1.15V
IPK
VIPK
0.23V ~ 1.0V
Figure 9.1 : iW1812 Functional Block Diagram
10 Theory of Operation
The iW1812 is a digital controller integrated with a power BJT. It uses a proprietary primary-side control technology to
eliminate the opto-isolated feedback and secondary regulation circuits required in traditional designs. This provides a
low-cost solution for low power AC/DC adapters. The core PWM processor uses fixed-frequency Discontinuous
Conduction Mode (DCM) operation at higher power levels and switches to variable frequency operation at light loads
to maximize efficiency. Furthermore, Dialog’s digital control technology enables fast dynamic response, tight output
regulation, and full-featured circuit protection with primary-side control.
The block diagram in Figure 9.1 shows the digital logic control block generates the switching on-time and off-time
information based on the output voltage and current feedback signal and provides instructions to dynamically control
the internal BJT base current. The ISENSE is an analog input configured to sense the primary current in a voltage
form. In order to achieve the peak current mode control and cycle-by-cycle current limit, the VIPK sets the threshold
for the ISENSE to compare with, and it varies in the range of 0.23V (typical) and 1.00V (typical) under different line and
load conditions. The system loop is automatically compensated internally by a digital error amplifier. Adequate system
phase margin and gain margin are guaranteed by design and no external analog components are required for loop
compensation. The iW1812 uses an advanced digital control algorithm to reduce system design time and increase
reliability.
Furthermore, accurate secondary constant-current operation is achieved without the need for any secondary-side
sense and control circuits.
The iW1812 uses adaptive multi-mode PWM/PFM control to dynamically change the BJT switching frequency for
efficiency, EMI, and power consumption optimization. In addition, it achieves unique BJT quasi-resonant switching
to further improve efficiency and reduce EMI. The built-in single-point fault protection features include over-voltage
protection (OVP), output-short-circuit protection (SCP), over-current protection (OCP), and ISENSE fault detection.
Dialog’s digital control scheme is specifically designed to address the challenges and trade-offs of power conversion
design. This innovative technology is ideal for balancing new regulatory requirements for green mode operation with
more practical design considerations such as the lowest possible cost, smallest size and high performance output
control.
Datasheet
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
10.1 Pin Detail
Pin 1 and Pin 2 – C
Collector pin of the internal power BJT.
Pin 4 – VCC
Power supply for the controller during normal operation. The controller will start up when VCC reaches 11.0V (typical)
and will shut-down when the VCC voltage is 4.0V (typical). A decoupling capacitor should be connected between the
VCC pin and GND.
Pin 5 – GND
Ground.
Pin 6 – VSENSE
Sense signal input from auxiliary winding. This provides the secondary voltage feedback used for output regulation.
Pin 7 – ISENSE
Primary current sense. It is used for cycle-by-cycle peak current control and limit.
Pin 8 – E
Emitter pin of the internal power BJT. This pin must be shorted to pin 7 (the ISENSE pin).
10.2 Start-up
Prior to start-up, the VCC pin is charged typically through start-up resistors. When VCC bypass capacitor is fully charged
to a voltage higher than the start-up threshold VCC(ST), the ENABLE signal becomes active to enable the control logic,
and the iW1812 begins to perform initial over-temperature protection check. When the internal die junction temperature
is below 100°C, the iW1812 commences soft-start function. During this start-up process, an adaptive soft-start control
algorithm is applied, during which the initial output pulses are small and gradually become larger until the full pulse
width is achieved. The peak current is limited cycle by cycle by the IPEAK comparator.
If at any time the VCC voltage drops below VCC(UVL) threshold then all the digital logic is reset. At this time the ENABLE
signal becomes low and the VCC capacitor is charged up again towards the start-up threshold.
Start-up
Sequencing
VCC(ST)
VCC
ENABLE
Figure 10.1 : Start-up Sequencing Diagram
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
10.3 Understanding Primary Feedback
Figure 10.2 illustrates a simplified flyback converter. When the switch Q1 conducts during tON(t), the current ig(t) is
directly drawn from the rectified sinusoid vg(t). The energy EG(t) is stored in the magnetizing inductance LM. The rectifying diode D1 is reverse biased and the load current IO is supplied by the secondary capacitor CO. When Q1 turns off,
D1 conducts and the stored energy Eg(t) is delivered to the output.
iin(t)
+
ig(t)
id(t)
N:1
D1
vg(t)
vin(t)
VO
+
CO
IO
VAUX
–
TS(t)
Q1
Figure 10.2 : Simplified Flyback Converter
In order to tightly regulate the output voltage, accurate information about the output voltage and load current must
be accurately conveyed. In the DCM flyback converter, this information can be read via the auxiliary winding or
the primary magnetizing inductance (LM). During the Q1 on-time, the load current is supplied from the output filter
capacitor CO. The voltage across LM is vg(t), if the voltage dropped across Q1 is zero. The current in Q1 ramps up
linearly at a rate of:
dig ( t )
dt
=
vg ( t )
(10.1)
LM
At the end of on-time, the current ramps up to:
ig _ peak ( t ) =
vg ( t ) × tON
LM
(10.2)
This current represents a stored energy of:
E
=
g
LM
2
× ig _ peak ( t )
2
(10.3)
When Q1 turns off at tO, ig(t) in LM forces a reversal of polarities on all windings. Ignoring the communication-time
caused by the leakage inductance LK at the instant of turn-off tO, the primary current transfers to the secondary at a
peak amplitude of:
id =
(t )
NP
× ig _ peak ( t )
NS
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
Assuming the secondary winding is master, and the auxiliary winding is slave,
1 VAUX = VO x
VAUX
NAUX
NS
0V
2 VAUX = -VIN x
NAUX
NP
Figure 10.3 : Auxiliary Voltage Waveforms
The auxiliary voltage is given by:
VAUX
=
N AUX
(VO + ∆V )
NS
(10.5)
and reflects the output voltage as shown in Figure 10.3.
The voltage at the load differs from the secondary voltage by a diode drop and IR losses. Therefore, if the secondary
voltage is always read at a constant secondary current, the difference between the output voltage and the secondary
voltage is a fixed ΔV. Furthermore, if the voltage can be read when the secondary current is small, ΔV is also small.
With the iW1812, ΔV can be ignored.
The real-time waveform analyzer in the iW1812 reads this information cycle by cycle. The part then generates a
feedback voltage VFB. The VFB signal accurately represents the output voltage under most circumstances and is used
to regulate the output voltage.
10.4 Constant Voltage Operation
After soft-start is completed, the digital control block measures the output conditions. It determines the output power
levels and adjusts the control system according to either a light or a heavy load. If this is in the normal range, the
device operates in the Constant Voltage (CV) mode, and changes the pulse width (TON) and off-time (TOFF) in order to
meet the output voltage regulation requirements.
If no voltage is detected on VSENSE, it is assumed that the auxiliary winding of the transformer is either open or shorted
and the iW1812 shuts down.
10.5 Current Limit and Constant Current Operation
The constant current (CC mode) is useful in battery charger and LED driver applications. During the operation in CC
mode the iW1812 regulates the output current at a constant level regardless of the output voltage, while avoiding continuous conduction mode.
To achieve this regulation the iW1812 senses the load current indirectly through the primary current. The primary
current is detected by the ISENSE pin through a resistor from the BJT emitter to ground.
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
CV mode
CC mode
Output Voltage
VNOM
Output Current
IOUT(CC)
Figure 10.4 : Power Envelope
10.6 Multi-Mode PWM/PFM Control and Quasi-Resonant Switching
The iW1812 uses a proprietary adaptive multi-mode PWM/PFM control to dramatically improve the light-load efficiency and thus the overall average efficiency.
During the constant voltage (CV) operation, the iW1812 normally operates in a pulse-width-modulation (PWM) mode
in heavy load conditions. In the PWM mode, the switching frequency keeps around constant. As the output load IOUT is
reduced, the on-time tON is decreased, and the controller adaptively transitions to a pulse-frequency-modulation (PFM)
voltage, but its off-time is modulated by the load current. With a decreasing load current, the off-time increases and
thus the switching frequency decreases.
When the switching frequency approaches to human ear audio band, the iW1812 transitions to a second level of
PWM mode, namely Deep PWM mode (DPWM). In the DPWM mode, the switching frequency keeps around 22kHz
in order to avoid audible noise. As the load current is further reduced, the iW1812 transitions to a second level of PFM
mode, namely Deep PFM mode (DPFM), which can reduce the switching frequency to a very low level. Although the
switching frequency drops across the audible frequency range in the DPFM mode, the output current in the power
converter has reduced to an insignificant level in the DPWM mode before transitioning to the DPFM mode. Therefore,
the power converter practically produces no audible noise, while achieving high efficiency across varying load conditions.
As the load current reduces to very low or no-load condition, the iW1812 transitions from the DPFM to the third level of
PWM mode, namely Deep-Deep PWM mode (DDPWM), where the switching frequency is fixed at around 1.9kHz.
The iW1812 also incorporates a unique proprietary quasi-resonant switching scheme that achieves valley-mode turn-on
for every PWM/PFM switching cycle, in all PFM and PWM modes, and in both CV and CC operations. This unique
feature greatly reduces the switching loss and dv/dt across the entire operating range of the power supply. Due to
the nature of quasi-resonant switching, the actual switching frequency can vary slightly cycle by cycle, providing the
additional benefit of reducing EMI. Together these innovative digital control architecture and algorithms enable the
iW1812 to achieve highest overall efficiency and lowest EMI, without causing audible noise over entire operating
range.
10.7 Less than 30mW No-Load Power with Fast Load Transient Response
The iW1812 features the distinctive DDPWM control at no-load conditions to help achieve very low no-load power
consumption (< 30mW for typical applications) and meanwhile to ensure fast dynamic load response. The power supply
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iW1812
Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
system designs including the pre-load resistor selection should ensure the power supply can stably operate in the
DDPWM mode at the steady-state no-load condition. If the pre-load resistor is too small, the no-load power consumption
will increase; on the other hand, if it is too large, the output voltage may increase and even cause over-voltage since
the switching frequency is fixed at around 1.9kHz. For typical designs, the pre-load resistor is in the range of 5kW to 8kW.
Aside from the appropriate use of pre-load resistor, the iW1812 enjoys a few other features to bring down no-load
power consumption as well. First, the iW1812 implements an intelligent low-power management technique that
achieves ultra-low chip operating current at the no-load, typically less than 400µA. Second, the use of the power
switch of BJT instead of MOSFET requires a lower driving voltage, enabling a low UVLO threshold as low as 4.0V
(typical). The power supply system design can fully utilize this low UVLO feature to have a low Vcc voltage at the
no-load operation in order to minimize the no-load power. In addition, the ultra-low start-up current during the
ramp-up of VCC towards the start-up threshold VCC(ST) (see Figure 8.5), allows for the use of high resistance start-up resistors to minimize their loss while still retaining reasonable turn-on time. All together these features ensure that with the
lowest system cost, power supplies built with the iW1812 can achieve less than 30mW no-load power consumption at
230 VAC input and very tight constant voltage and constant current regulation over the entire operating range including
the no-load operation.
While achieving super-low no-load power consumption, the iW1812 implements innovative proprietary digital control
technology to intelligently detect any load transient events, and achieve fast dynamic load response for both one-time and
repetitive load transients. In particular, for load transients that are demanded in some applications as from absolutely no
load to full load, the iW1812 can still guarantee a fast enough response to meet the most stringent requirements, with
the no-load operating frequency designed at around 1.9kHz.
10.8 Variable Frequency Operation Mode
During each of the switching cycles, the falling edge of VSENSE is checked. If the falling edge of VSENSE is not detected,
the off-time is extended until the falling edge of VSENSE is detected. The maximum transformer reset time allowed is
125μs. When the transformer reset time reaches 125μs, the iW1812 shuts off.
10.9 Internal Loop Compensation
The iW1812 incorporates an internal Digital Error Amplifier with no requirement for external loop compensation. For
a typical power supply design, the loop stability is guaranteed to provide at least 45 degrees of phase margin and
-20dB of gain margin.
10.10 Voltage Protection Features
The secondary maximum output DC voltage is limited by the iW1812. When the VSENSE signal exceeds the output
OVP threshold at point 1 (as shown in Figure 10.3), the iW1812 shuts down.
The iW1812 protects against input line under-voltage by setting a maximum TON time. Since output power is
proportional to the squared VINTON product, for a given output power, the TON increases as the VIN decreases. Thus by
knowing when the maximum TON time occurs, the iW1812 detects that the minimum VIN is reached, and then it shuts
down. The maximum tON limit is set to 15.6μs. Also, the iW1812 monitors the voltage on the VCC pin and when the
voltage on this pin is below UVLO threshold the IC shuts down immediately.When any of these faults is met the IC
remains biased to discharge the VCC supply. Once VCC drops below the UVLO threshold, the controller resets itself and
then initiates a new soft-start cycle. The controller continues attempting start-up until the fault condition is removed.
10.11 PCL, OCP and SRS Protection
The peak-current limit (PCL), over-current protection (OCP) and sense-resistor short protection (SRSP) are built-in
features in the iW1812. With the ISENSE pin the iW1812 is able to monitor the peak primary current. This allows for
cycle-by-cycle peak current control and limit. When the peak primary current multiplied by the ISENSE resistor is greater
than 1.15V, over-current protection (OCP) is detected and the IC immediately turns off the base driver until the next
cycle. The output driver sends out a switching pulse in the next cycle, and the switching pulse continues if the OCP
threshold is not reached; or, the switching pulse turns off again if the OCP threshold is reached. If the OCP occurs for
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Off-Line Digital Green-Mode PWM Controller
Integrated with Power BJT and OTP
several consecutive switching cycles, the iW1812 shuts down.
If the ISENSE resistor is shorted, there is a potential danger that the over-current condition is not detected. Thus, the
IC is designed to detect this sense-resistor-short fault after start-up and immediate shutdown. The VCC is discharged
since the IC remains biased. Once the VCC drops below the UVLO threshold, the controller resets itself and then
initiates a new soft-start cycle. The controller continues attempting to start up, but does not fully start up until the fault
condition is removed.
10.12 Dynamic Base Current Control
An important feature of the iW1812 is that it directly drives an internal BJT switching device with dynamic base current
control to optimize performance. The BJT base current ranges from 10mA to 31mA, and is dynamically controlled according to the power supply load change. The higher the output power, the higher the base current. Specifically, the
base current is related to VIPK, as shown in Figure 10.5.
Base Drive Current (mA)
35
30
25
20
15
10
5
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
VIPK (V)
0.9 1.0 1.1
Figure 10.5 : Base Drive Current vs. VIPK
10.13 Internal Over-Temperature Protection
The iW1812 features an internal over-temperature protection (OTP), which will shut down the device if the internal die
junction temperature reaches above 150°C (typical). The device will be kept off until the junction temperature drops
below 100°C (typical), when the device initiates a new soft-start process to build up the output voltage.
10.14 Thermal Design
The iW1812 may be installed inside a small enclosure, where space and air volumes are constrained. Under these circumstances θJA (thermal resistance, junction-to-ambient) measurements do not provide useful information for this type
of application. Hence we have also provided ψJB which estimates the increase in die junction temperature relative to
the PCB surface temperature. Figure 10.6 shows the PCB surface temperature is measured at the IC’s GND pin pad.
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Off-Line Digital Green-Mode PWM Controller
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ψJ-BJT
ψJB
J
J
B
BJT collector
PCB Top Copper Trace
Collector pin
TJ
GND pin
IC Die
Printed Circuit Board
Note: For illustrative purposes only does not represent a correct pinout or size of chip
Figure 10.6 : Thermal Resistance
The actual IC power dissipation is related to the power supply application circuit, component selection and operation
conditions. The maximum IC power dissipation should be used to estimate the maximum junction temperature. For a
typical 3-W power supply, the power dissipation can be around 500mW.
The output power table in Section 3.0 recommends maximum practical continuous output power level be achieved
under the following conditions:
●● Typical 5V-output power supply designs with a Schottky rectifier diode
●● Ambient temperature of 50°C for open frame and adapter enclosure internal temperature of 60°C in a
non-ventilated environment
●● AC Input voltage is 85VAC at 47Hz
●● Minimum bulk capacitor voltage is 90V for open frame and 70V for adapter
●● The iW1812 device is mounted on PCB with no special enhancement for heatsinking and the emitter pin
temperature is kept below 90°C
Under a given power dissipation, reducing the GND, emitter, and collector pin temperature reduces the junction
temperature. Generally, increasing the PCB area and associated amount of copper trace reduces the junction
temperature. In particular, the power BJT is a power source and therefore the PCB plating area attached to the two
collector pins and the emitter pin can be reasonably large to gain the thermal benefits without violating the high
voltage creepage requirements if higher output power is desired. Higher output power is also achievable if bulk
capacitor voltage is higher, design is for high line only, design components temperature restriction limit is higher,
ambient temperature is lower, or extra metal piece/heat spreader is attached to related pins or package.
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Off-Line Digital Green-Mode PWM Controller
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11 Physical Dimensions
7-Lead Small Outline (SOIC) Package
E
8
5
1
4
H
e
h x 45°
A1
COPLANARITY
0.10 (0.004)
B
SEATING
PLANE
C
MIN
MAX
MIN
MAX
A
0.060
0.068
1.52
1.73
A1
0.004
0.008
0.10
0.20
B
0.014
0.018
0.36
0.46
C
0.007
0.010
0.18
0.25
D
0.188
0.197
4.78
5.00
E
0.150
0.157
3.81
3.99
e
A
α
Inches
Symbol
D
L
0.050 BSC
Millimeters
1.270 BSC
H
0.230
0.244
5.84
6.20
h
0.010
0.016
0.25
0.41
L
0.023
0.029
0.58
0.74
α
0°
8°
Compliant to JEDEC Standard MS12F
Controlling dimensions are in inches; millimeter dimensions are for reference only
This product is RoHS compliant and Halide free.
Soldering Temperature Resistance:
[a] Package is IPC/JEDEC Std 020D Moisture Sensitivity Level 1
[b] Package exceeds JEDEC Std No. 22-A111 for Solder Immersion Resistance; package can withstand
10 s immersion < 270˚C
Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shall
not exceed 0.15 mm per end. Dimension E1 does not include interlead flash or protrusion. Interlead flash or
protrusion shall not exceed 0.25 mm per side.
The package top may be smaller than the package bottom. Dimensions D and E1 are determined at the
outermost extremes of the plastic bocy exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but
including any mismatch between the top and bottom of the plastic body.
12 Ordering Information
Part Number
Package
Description
iW1812-20
SOIC-7
Tape & Reel1
Note 1: Tape & Reel packing quantity is 2,500 per reel. Minimum ordering quantity is 2,500.
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