TNY263-268
TinySwitch-II
Family
®
Enhanced, Energy Efficient, Low Power
Off-line Switcher
Product Highlights
+
TinySwitch-II Features Reduce System Cost
•
Fully integrated auto-restart for short circuit and open loop fault
protection – saves external component costs
•
Built-in circuitry practically eliminates audible noise with ordinary
dip-varnished transformer
•
Programmable line undervoltage detect feature prevents power
on/off glitches – saves external components
•
Frequency jittering dramatically reduces EMI (~10 dB)
– minimizes EMI filter component costs
•
132 kHz operation reduces transformer size – allows use of
EF12.6 or EE13 cores for low cost and small size
•
Very tight tolerances and negligible temperature variation on key
parameters eases design and lowers cost
•
Lowest component count switcher solution
•
Expanded scalable device family for low system cost
Better Cost/Performance over RCC & Linears
•
Lower system cost than RCC, discrete PWM and other
integrated/hybrid solutions
•
Cost effective replacement for bulky regulated linears
•
Simple ON/OFF control – no loop compensation needed
•
No bias winding – simpler, lower cost transformer
•
Simple design practically eliminates rework in manufacturing
EcoSmart – Extremely Energy Efficient
•
No load consumption <50 mW with bias winding and
<250 mW without bias winding at 265 VAC input
•
Meets California Energy Commission (CEC), Energy Star, and
EU requirements
•
Ideal for cell-phone charger and PC standby applications
High Performance at Low Cost
•
High voltage powered – ideal for charger applications
•
High bandwidth provides fast turn on with no overshoot
•
Current limit operation rejects line frequency ripple
•
Built-in current limit and thermal protection improves safety
®
+
Optional
UV Resistor
DC
Output
-
Wide-Range
HV DC Input
TinySwitch-II
S
D
EN/UV
BP
-
PI-2684-021809
Figure 1.
Typical Standby Application.
Output Power Table
230 VAC ± 15%
Product
3
85-265 VAC
Adapter
1
3.7 W
4W
5.5 W
6W
8W
10 W
Open
Frame
2
4.7 W
6W
7.5 W
9.5 W
12 W
15 W
Adapter
1
5W
5.5 W
8.5 W
10 W
13 W
16 W
Open
Frame
2
7.5 W
9W
11 W
15 W
19 W
23 W
TNY263 P/G
TNY264 P/G
TNY265 P/G
TNY266 P/G
TNY267 P/G
TNY268 P/G
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at 50 °C ambient.
2. Minimum practical continuous power in an open frame design with adequate
heat sinking, measured at 50 °C ambient (See Key Applications
Considerations).
3. Packages: P: DIP-8B, G: SMD-8B. Please see Part Ordering Information.
Description
TinySwitch-II integrates a 700 V power MOSFET, oscillator, high
voltage switched current source, current limit and thermal
shutdown circuitry onto a monolithic device. The start-up and
operating power are derived directly from the voltage on the
DRAIN pin, eliminating the need for a bias winding and
associated circuitry. In addition, the TinySwitch-II devices
incorporate auto-restart, line undervoltage sense, and frequency
jittering. An innovative design minimizes audio frequency
components in the simple ON/OFF control scheme to practically
eliminate audible noise with standard taped/varnished
transformer construction. The fully integrated auto-restart circuit
safely limits output power during fault conditions such as output
short circuit or open loop, reducing component count and
secondary feedback circuitry cost. An optional line sense resistor
externally programs a line undervoltage threshold, which
eliminates power down glitches caused by the slow discharge of
input storage capacitors present in applications such as standby
supplies. The operating frequency of 132 kHz is jittered to
significantly reduce both the quasi-peak and average EMI,
minimizing filtering cost.
www.powerint.com
February 2009
TNY263-268
BYPASS
(BP)
REGULATOR
5.8 V
LINE UNDER-VOLTAGE
240 A
50 A
FAULT
PRESENT
DRAIN
(D)
+
-
CURRENT
LIMIT STATE
MACHINE
5.8 V
4.8 V
BYPASS PIN
UNDER-VOLTAGE
AUTO-
RESTART
COUNTER
6.3 V
RESET
VI
LIMIT
CURRENT LIMIT
COMPARATOR
ENABLE
-
+
JITTER
CLOCK
1.0 V + VT
DCMAX
THERMAL
SHUTDOWN
OSCILLATOR
ENABLE/
UNDER-
VOLTAGE
(EN/UV)
1.0 V
S
Q
R
Q
LEADING
EDGE
BLANKING
SOURCE
(S)
PI-2643-030701
Figure 2.
Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
Power MOSFET drain connection. Provides internal operating
current for both start-up and steady-state operation.
BYPASS (BP) Pin:
Connection point for a 0.1
μF
external bypass capacitor for the
internally generated 5.8 V supply.
ENABLE/UNDERVOLTAGE (EN/UV) Pin:
This pin has dual functions: enable input and line undervoltage
sense. During normal operation, switching of the power
MOSFET is controlled by this pin. MOSFET switching is
terminated when a current greater than 240
μA
is drawn from
this pin. This pin also senses line undervoltage conditions
through an external resistor connected to the DC line voltage.
If there is no external resistor connected to this pin,
TinySwitch-II detects its absence and disables the line
undervoltage function.
SOURCE (S) Pin:
Control circuit common, internally connected to output
MOSFET source.
P Package (DIP-8B)
G Package (SMD-8B)
BP
S
S
EN/UV
1
2
3
4
8
7
S (HV RTN)
S (HV RTN)
5
D
PI-2685-101600
Figure 3.
Pin Configuration.
SOURCE (HV RTN) Pin:
Output MOSFET source connection for high voltage return.
2
Rev. H 02/09
www.powerint.com
TNY263-268
TinySwitch-II Functional Description
TinySwitch-II combines a high voltage power MOSFET switch
with a power supply controller in one device. Unlike
conventional PWM (pulse width modulator) controllers,
TinySwitch-II uses a simple ON/OFF control to regulate the
output voltage.
The TinySwitch-II controller consists of an oscillator, enable
circuit (sense and logic), current limit state machine,
5.8 V regulator, BYPASS pin undervoltage circuit, over-
temperature protection, current limit circuit, leading edge
blanking and a 700 V power MOSFET. TinySwitch-II
incorporates additional circuitry for line undervoltage sense,
auto-restart and frequency jitter. Figure 2 shows the functional
block diagram with the most important features.
Oscillator
The typical oscillator frequency is internally set to an average
of 132 kHz. Two signals are generated from the oscillator: the
maximum duty cycle signal (DC
MAX
) and the clock signal that
indicates the beginning of each cycle.
The TinySwitch-II oscillator incorporates circuitry that
introduces a small amount of frequency jitter, typically 8 kHz
peak-to-peak, to minimize EMI emission. The modulation rate
of the frequency jitter is set to 1 kHz to optimize EMI reduction
for both average and quasi-peak emissions. The frequency
jitter should be measured with the oscilloscope triggered at
the falling edge of the DRAIN waveform. The waveform in
Figure 4 illustrates the frequency jitter of the TinySwitch-II.
Enable Input and Current Limit State Machine
The enable input circuit at the EN/UV pin consists of a low
impedance source follower output set at 1.0 V. The current
through the source follower is limited to 240
μA.
When the
current out of this pin exceeds 240
μA,
a low logic level
(disable) is generated at the output of the enable circuit. This
enable circuit output is sampled at the beginning of each cycle
on the rising edge of the clock signal. If high, the power
MOSFET is turned on for that cycle (enabled). If low, the power
PI-2741-041901
MOSFET remains off (disabled). Since the sampling is done
only at the beginning of each cycle, subsequent changes in
the EN/UV pin voltage or current during the remainder of the
cycle are ignored.
The current limit state machine reduces the current limit by
discrete amounts at light loads when TinySwitch-II is likely to
switch in the audible frequency range. The lower current limit
raises the effective switching frequency above the audio range
and reduces the transformer flux density, including the
associated audible noise. The state machine monitors the
sequence of EN/UV pin voltage levels to determine the load
condition and adjusts the current limit level accordingly in
discrete amounts.
Under most operating conditions (except when close to no-
load), the low impedance of the source follower keeps the
voltage on the EN/UV pin from going much below 1.0 V in the
disabled state. This improves the response time of the
optocoupler that is usually connected to this pin.
5.8 V Regulator and 6.3 V Shunt Voltage Clamp
The 5.8 V regulator charges the bypass capacitor connected
to the BYPASS pin to 5.8 V by drawing a current from the
voltage on the DRAIN pin whenever the MOSFET is off. The
BYPASS pin is the internal supply voltage node for the
TinySwitch-II. When the MOSFET is on, the TinySwitch-II
operates from the energy stored in the bypass capacitor.
Extremely low power consumption of the internal circuitry
allows TinySwitch-II to operate continuously from current it
takes from the DRAIN pin. A bypass capacitor value of 0.1
μF
is sufficient for both high frequency decoupling and energy
storage.
In addition, there is a 6.3 V shunt regulator clamping the
BYPASS pin at 6.3 V when current is provided to the BYPASS
pin through an external resistor. This facilitates powering of
TinySwitch-II externally through a bias winding to decrease the
no-load consumption to about 50 mW.
BYPASS Pin Undervoltage
The BYPASS pin undervoltage circuitry disables the power
MOSFET when the BYPASS pin voltage drops below 4.8 V.
Once the BYPASS pin voltage drops below 4.8 V, it must rise
back to 5.8 V to enable (turn-on) the power MOSFET.
Over Temperature Protection
The thermal shutdown circuitry senses the die temperature.
The threshold is typically set at 135
°C
with 70
°C
hysteresis.
When the die temperature rises above this threshold the
power MOSFET is disabled and remains disabled until the die
temperature falls by 70
°C,
at which point it is re-enabled. A
large hysteresis of 70
°C
(typical) is provided to prevent
overheating of the PC board due to a continuous fault
condition.
Current Limit
The current limit circuit senses the current in the power
MOSFET. When this current exceeds the internal threshold
(I
LIMIT
), the power MOSFET is turned off for the remainder of
600
500
V
DRAIN
400
300
200
100
0
136 kHz
128 kHz
0
Figure 4.
Frequency Jitter.
5
Time (μs)
10
3
www.powerint.com
Rev. H 02/09
TNY263-268
that cycle. The current limit state machine reduces the current
limit threshold by discrete amounts under medium and light
loads.
The leading edge blanking circuit inhibits the current limit
comparator for a short time (t
LEB
) after the power MOSFET is
turned on. This leading edge blanking time has been set so
that current spikes caused by capacitance and secondary-
side rectifier reverse recovery time will not cause premature
termination of the switching pulse.
Auto-Restart
In the event of a fault condition such as output overload,
output short circuit, or an open loop condition, TinySwitch-II
enters into auto-restart operation. An internal counter clocked
by the oscillator gets reset every time the EN/UV pin is pulled
low. If the EN/UV pin is not pulled low for 50 ms, the power
MOSFET switching is normally disabled for 850 ms (except in
the case of line undervoltage condition, in which case it is
disabled until the condition is removed). The auto-restart
alternately enables and disables the switching of the power
MOSFET until the fault condition is removed. Figure 5
illustrates auto-restart circuit operation in the presence of an
output short circuit.
In the event of a line undervoltage condition, the switching of
the power MOSFET is disabled beyond its normal 850 ms time
until the line undervoltage condition ends.
Line Undervoltage Sense Circuit
The DC line voltage can be monitored by connecting an
external resistor from the DC line to the EN/UV pin. During
power-up or when the switching of the power MOSFET is
disabled in auto-restart, the current into the EN/UV pin must
exceed 49
μA
to initiate switching of the power MOSFET.
During power-up, this is accomplished by holding the BYPASS
pin to 4.8 V while the line undervoltage condition exists. The
BYPASS pin then rises from 4.8 V to 5.8 V when the line
undervoltage condition goes away. When the switching of the
power MOSFET is disabled in auto-restart mode and a line
undervoltage condition exists, the auto-restart counter is
stopped. This stretches the disable time beyond its normal
850 ms until the line undervoltage condition ends.
The line undervoltage circuit also detects when there is no
external resistor connected to the EN/UV pin (less than
~2
μA
into the pin). In this case the line undervoltage function
is disabled.
TinySwitch-II Operation
TinySwitch-II devices operate in the current limit mode. When
enabled, the oscillator turns the power MOSFET on at the
beginning of each cycle. The MOSFET is turned off when the
current ramps up to the current limit or when the DC
MAX
limit is
reached. Since the highest current limit level and frequency of
a TinySwitch-II design are constant, the power delivered to the
load is proportional to the primary inductance of the transformer
and peak primary current squared. Hence, designing the supply
involves calculating the primary inductance of the transformer
for the maximum output power required. If the TinySwitch-II is
appropriately chosen for the power level, the current in the
calculated inductance will ramp up to current limit before the
DC
MAX
limit is reached.
Enable Function
TinySwitch-II senses the EN/UV pin to determine whether or
not to proceed with the next switching cycle as described
earlier. The sequence of cycles is used to determine the
current limit. Once a cycle is started, it always completes the
cycle (even when the EN/UV pin changes state half way
through the cycle). This operation results in a power supply in
which the output voltage ripple is determined by the output
capacitor, amount of energy per switch cycle and the delay of
the feedback.
The EN/UV pin signal is generated on the secondary by
comparing the power supply output voltage with a reference
voltage. The EN/UV pin signal is high when the power supply
output voltage is less than the reference voltage.
In a typical implementation, the EN/UV pin is driven by an
optocoupler. The collector of the optocoupler transistor is
connected to the EN/UV pin and the emitter is connected to
the SOURCE pin. The optocoupler LED is connected in series
with a Zener diode across the DC output voltage to be
regulated. When the output voltage exceeds the target
regulation voltage level (optocoupler LED voltage drop plus
Zener voltage), the optocoupler LED will start to conduct,
pulling the EN/UV pin low. The Zener diode can be replaced
by a TL431 reference circuit for improved accuracy.
ON/OFF Operation with Current Limit State Machine
The internal clock of the TinySwitch-II runs all the time. At the
beginning of each clock cycle, it samples the EN/UV pin to
decide whether or not to implement a switch cycle, and based
on the sequence of samples over multiple cycles, it determines
300
200
100
0
10
V
V
DRAIN
5
0
DC-OUTPUT
0
1000
2000
Time (ms)
Figure 5.
TinySwitch-II Auto-Restart Operation.
4
Rev. H 02/09
PI-2699-030701
www.powerint.com
TNY263-268
the appropriate current limit. At high loads, when the EN/UV
pin is high (less than 240
μA
out of the pin), a switching cycle
with the full current limit occurs. At lighter loads, when EN/UV
is high, a switching cycle with a reduced current limit occurs.
At near maximum load, TinySwitch-II will conduct during
nearly all of its clock cycles (Figure 6). At slightly lower load, it
will “skip” additional cycles in order to maintain voltage
regulation at the power supply output (Figure 7). At medium
loads, cycles will be skipped and the current limit will be
reduced (Figure 8). At very light loads, the current limit will be
reduced even further (Figure 9). Only a small percentage of
cycles will occur to satisfy the power consumption of the
power supply.
The response time of the TinySwitch-II ON/OFF control
scheme is very fast compared to normal PWM control. This
provides tight regulation and excellent transient response.
Power Up/Down
The TinySwitch-II requires only a 0.1
μF
capacitor on the
BYPASS pin. Because of its small size, the time to charge this
capacitor is kept to an absolute minimum, typically 0.6 ms.
Due to the fast nature of the ON/OFF feedback, there is no
overshoot at the power supply output. When an external
resistor (2 MΩ) is connected from the positive DC input to the
EN/UV pin, the power MOSFET switching will be delayed
during power-up until the DC line voltage exceeds the
threshold (100 V). Figures 10 and 11 show the power-up timing
waveform of TinySwitch-II in applications with and without an
external resistor (2 MΩ) connected to the EN/UV pin.
During power-down, when an external resistor is used, the
power MOSFET will switch for 50 ms after the output loses
regulation. The power MOSFET will then remain off without
any glitches since the undervoltage function prohibits restart
when the line voltage is low.
Figure 12 illustrates a typical power-down timing waveform of
TinySwitch-II. Figure 13 illustrates a very slow power-down
timing waveform of TinySwitch-II as in standby applications.
The external resistor (2 MΩ) is connected to the EN/UV pin in
this case to prevent unwanted restarts.
PI-2749-050301
V
EN
CLOCK
D
MAX
I DRAIN
V DRAIN
Figure 6.
TinySwitch-II Operation at Near Maximum Loading.
The TinySwitch-II does not require a bias winding to provide
power to the chip, because it draws the power directly from
the DRAIN pin (see Functional Description above). This has
V
EN
CLOCK
V
EN
CLOCK
D
D
MAX
MAX
I DRAIN
I DRAIN
V DRAIN
V DRAIN
PI-2667-090700
PI-2377-091100
Figure 7.
TinySwitch-II Operation at Moderately Heavy Loading.
Figure 8.
TinySwitch-II Operation at Medium Loading.
5
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Rev. H 02/09
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