IW1692 Datasheet, PDF (9/18 Pages) Dialog Semiconductor – Low-Power Off-line Digital PWM Controller

iW1692
Low-Power Off-line Digital PWM Controller
10.0 Design Example
10.1 Design Procedure
This design example gives the procedure for a flyback
converter using iW1692. Refer to figure 12.0.1 for the
application circuit. The design objectives for this adapter
are given in table 10.1. It meets UL, IEC, and CEC
requirements.
Determine the Design Specifications
(Vout, Iout_max, Vin_max, Vin_min, efficiency, and ripple)
Determine Output Voltage
Parameter
Input Voltage
Frequency
No Load Input
Output Voltage
Output Current
Output Ripple
Power Out
Symbol
V_IN
f_IN
P_IN
V_{OUT_PCB}
I_OUT
V_RIPPLE
P_OUT
Range
s _{85 - 264 VRMS}
n _{47 - 64 Hz}
ig ^200 mW
4.95 - 5.05 V
s_1 A
e_<100 mV
D ^5 W
Determine Rvin Resistors
Determine Turns Ratio
Determine Input Bulk Capacitance
Determine Current Sensing Resistor
Determine Magnetizing Inductance
Determine Primary Turns
CEC Efficiency
h
65%
Table 10.1 iW1692 Design Specification Table
ew 10.2 Output Voltage
Use equation 10.1 for V_OUT in the following equations, where
N _{VFD is the forward voltage of the output diode:}
r _{= VOUT VOUT (PCB) + VFD}
(10.1)
Fo ^{Since no cable is used and the forward drop on the output}
Determine Secondary Turns
d _{Can you wind this transformer ?}
No
e Yes
nd ^{Determine Bias Turns}
Determine Vsense Turns and Resistors
Determine Output Capacitance
me ^{Determine Snubber Network}
diode (V_FD) is 500 mV, V_OUT is 5.0 V.
10.3 Input Selection
V_IN resistors are chosen primarily to scale down the input
voltage for the IC. The scale factor for the input voltage in the
IC is 0.0043 and the internal impedance of this pin is 20 kΩ.
Therefore, the V_IN resistors should equate to:
= R_Vin
20kW _{− 2= 0kW}
0.0043
4.63M W
(10.2)
Determine Ton Delay Compensation
m _Finish
Not ^{Reco Figure 10.0.1 iW1692 Design Flow Chart}
From equation 10.2, ideally R_VIN should be 4.63 MΩ because
R10 and R11 add up to approximately 4.6 MΩ. By selecting
the value of R_VIN, the (V_IN·T_ON)_{MAX_LIMIT} and (V_IN·T_ON)_PFM are
determined:
(V_IN
⋅ T_ON
)_{MAX _ LIMIT}
= 0.0043×

900V ⋅m s
20kW



R_Vin
+
20kW


(10.3)
(V_IN
) ⋅T_{ON PFM}
=0.0043×

185V ⋅m s
20kW



R_Vin
+
20kW


(10.4)
Keep in mind by changing R_VIN to be something other than
4.63 MΩ the minimum and maximum input voltage for start-
up will also change.
Rev. 2.0
iW1692
February 13, 2012

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