Key Applications Design Considerations - Power integrations InnoSwitch3 Application Note

Application Note

Key Applications Design Considerations

Output Power Table
The output power table in the data sheet (Table 1) represents the
maximum practical continuous output power that can be obtained
under the following conditions:
1. The minimum DC input voltage is 90 V or higher for 85 VAC input,
220 V or higher for 230 VAC input (or 115 VAC with a voltage-
doubler). Input capacitor voltage should be sized to meet these
criteria for AC input designs.
2. Efficiency assumptions depend on power level. Smallest device
power level assumes efficiency >84% increasing to >89% for the
largest device and are quite conservative.
3. Transformer primary inductance tolerance of ±10%.
4. Reflected output voltage (V
OR
minimum input voltage for universal line and K
designs.
5. Maximum conduction loss for adapters is limited to 0.6 W, 0.8 W
for open frame designs.
6. Increased current limit is selected for peak and open frame power
designs and standard current limit for adapter designs.
+V
BULK
C
BIAS
C
R
IN
Z
InnoSwitch3
V
RZ
R
BP
Primary FET
D
and Controller
B
a. Primary-side OVP with high current pushed into BPP via Zener V
Figure 18. Output Overvoltage Protection Circuits.
22
Rev. A 10/18
) is set to maintain K = 0.8 at
P
= 1 for high-line
P
D
BIAS
N
B
D V
S BPP
PI-8481-101017
.
RZ
c. Secondary-side OVP with high current pushed into BPS via two diodes (for 5 V output only).
7. The part is board mounted with SOURCE pins soldered to a
sufficient area of copper and/or a heat sink to keep the SOURCE
pin temperature at or below 110 °C.
8. Ambient temperature of 50 °C for open frame designs and 40 °C
for sealed adapters is assured.
9. To prevent reduced power delivery, due to premature termination
of switching cycles, a transient K
prevents the initial current limit (I
MOSFET turn-ON.
10. It is unique feature in InnoSwitch3 that a designer can set the
operating switching frequency between 25 kHz to 95 kHz depending
on the transformer design. One of the ways to effectively lower
device temperature is to design the transformer to operate at low
switching frequency, a good starting point is 60 kHz for larger
device such as size 8, but for smaller device such size 2, 80 kHz is
appropriate.
Primary-Side Overvoltage Protection
Primary-side output overvoltage protection provided by the InnoSwitch3 IC
uses an internal latch that is triggered by a threshold current of I
flowing into the PRIMARY BYPASS pin. For the bypass capacitor to be
effective as a high frequency filter, the capacitor should be located as
b. Secondary-side OVP with high current pushed into BPS via Zener V
resistor R .
Z
V
OUT
FB
Diode
OVP
C
BPS
InnoSwitch3
Secondary
Control IC
IS
RTN
PI-8480-091318
limit of ≥0.5 is used. This
P
) from being exceeded at
INT
Zener
V
OVP
OUT
R
Z
FB
V
Z
D
B
C V = (V × 1.25) –
Z OUT
BPS
(4 × 4 – V
BPS
InnoSwitch3
Secondary
Control IC
IS
RTN
PI-8476-101017
www.power.com
AN-72
SD
)
and
Z