InnoSwitch3-EP
1.0ꢂ
1.0
Primary Controller
InnoSwitch3-EP has variable frequency QR controller plus CCM/CrM/
DCM operation for enhanced efficiency and extended output power
capability.
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0.ꢅ
PRIMARY BYPASS Pin Regulator
The PRIMARY BYPASS pin has an internal regulator that charges the
PRIMARY BYPASS pin capacitor to VBPP by drawing current from the
DRAIN pin whenever the power MOSFET is off. The PRIMARY
BYPASS pin is the internal supply voltage node. When the power
MOSFET is on, the device operates from the energy stored in the
PRIMARY BYPASS pin capacitor.
0.8ꢂ
0.8
In addition, a shunt regulator clamps the PRIMARY BYPASS pin
voltage to VSHUNT when current is provided to the PRIMARY BYPASS
pin through an external resistor. This allows the InnoSwitch3-EP to
be powered externally through a bias winding, decreasing the no-load
consumption to less than 15 mW in a 5 V output design.
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ꢀ0
ꢁ0
ꢂ0
ꢃ0
ꢄ0
80
ꢅ0
100
Stꢀꢁꢂꢃ-Stꢁtꢀ Switchinꢄ ꢅꢆꢀꢇꢈꢀncꢃ ꢉꢊꢋꢌꢍ
Primary Bypass ILIM Programming
Figure 6. Normalized Primary Current vs. Frequency.
InnoSwitch3-EP ICs allows the user to adjust current limit (ILIM)
settings through the selection of the PRIMARY BYPASS pin capacitor
value. A ceramic capacitor can be used.
Current Limit Operation
The primary-side controller has a current limit threshold ramp that is
linearly decreasing to the time from the end of the previous primary
switching cycle (i.e. from the time the primary MOSFET turns off at
the end of a switching cycle).
There are 2 selectable capacitor sizes - 0.47 mF and 4.7 mF for setting
standard and increased ILIM settings respectively.
Primary Bypass Undervoltage Threshold
The PRIMARY BYPASS pin undervoltage circuitry disables the power
MOSFET when the PRIMARY BYPASS pin voltage drops below ~4.5 V
(VBPP - VBP(H)) in steady-state operation. Once the PRIMARY BYPASS
pin voltage falls below this threshold, it must rise to VSHUNT to
re-enable turn-on of the power MOSFET.
This characteristic produces a primary current limit that increases as
the switching frequency (load) increases (Figure 6).
This algorithm enables the most efficient use of the primary switch
with the benefit that this algorithm responds to digital feedback
information immediately when a feedback switching cycle request is
received.
Primary Bypass Output Overvoltage Function
The PRIMARY BYPASS pin has a latching OV protection feature. A
Zener diode in parallel with the resistor in series with the PRIMARY
BYPASS pin capacitor is typically used to detect an overvoltage on the
primary bias winding and activate the protection mechanism. In the
event that the current into the PRIMARY BYPASS pin exceeds ISD, the
device will latch-off or disable the power MOSFET switching for a time
At high load, switching cycles have a maximum current approaching
100% ILIM. This gradually reduces to 30% of the full current limit as
load decreases. Once 30% current limit is reached, there is no
further reduction in current limit (since this is low enough to avoid
audible noise). The time between switching cycles will continue to
increase as load reduces.
t
AR(OFF), after which time the controller will restart and attempt to
return to regulation (see Secondary Fault Response in the Feature
Code Addenda).
Jitter
The normalized current limit is modulated between 100% and 95%
at a modulation frequency of fM. This results in a frequency jitter of
~7 kHz with average frequency of ~100 kHz.
VOUT OV protection is also included as an integrated feature on the
secondary controller (see Output Voltage Protection).
Auto-Restart
Over-Temperature Protection
In the event a fault condition occurs (such as an output overload,
output short-circuit, or external component/pin fault), the
InnoSwitch3-EP enters auto-restart (AR) or latches off. The latching
condition is reset by bringing the PRIMARY BYPASS pin below ~3 V or
The thermal shutdown circuitry senses the primary MOSFET die
temperature. The threshold is set to TSD with either a hysteretic or
latch-off response.
Hysteretic response: If the die temperature rises above the threshold,
the power MOSFET is disabled and remains disabled until the die
temperature falls by TSD(H) at which point switching is re-enabled. A
large amount of hysteresis is provided to prevent over-heating of the
PCB due to a continuous fault condition.
by going below the UNDER/OVER INPUT VOLTAGE pin UV (IUV-
)
threshold.
In auto-restart, switching of the power MOSFET is disabled for tAR(OFF)
.
There are 2 ways to enter auto-restart:
1. Continuous secondary requests at above the overload detection
Latch-off response: If the die temperature rises above the threshold
the power MOSFET is disabled. The latching condition is reset by
bringing the PRIMARY BYPASS pin below VBPP(RESET) or by going below
the UNDER/OVER INPUT VOLTAGE pin UV (IUV-) threshold.
frequency fOVL (~110 kHz) for longer than 82 ms (tAR).
2. No requests for switching cycles from the secondary for >tAR(SK)
.
The second is included to ensure that if communication is lost, the
primary tries to restart. Although this should never be the case in
normal operation, it can be useful when system ESD events (for
example) causes a loss of communication due to noise disturbing the
secondary controller. The issue is resolved when the primary restarts
after an auto-restart off-time.
4
Rev. D 08/18
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