TNY264/266-268
TinySwitch-II
Family
Enhanced, Energy Efficient,
Low Power Off-line Switcher
Figure 1. Typical Standby Application.
Product Highlights
TinySwitch-II
Features Reduce System Cost
Fully integrated auto-restart for short circuit and open
loop fault protectionsaves external component costs
Built-in circuitry practically eliminates audible noise with
ordinary varnished transformer
Programmable line under-voltage detect feature prevents
power on/off glitchessaves external components
Frequency jittering dramatically reduces EMI (~10 dB)
minimizes EMI filter component costs
132 kHz operation reduces transformer sizeallows 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
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 controlno loop compensation needed
No bias windingsimpler, lower cost transformer
EcoSmart
Extremely Energy Efficient
No load consumption < 50 mW with bias winding and
< 250 mW without bias winding at 265 VAC input
Meets Blue Angel, Energy Star, and EC requirements
Ideal for cell-phone charger and PC standby applications
High Performance at Low Cost
High voltage poweredideal 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
Description
TinySwitch-II maintains the simplicity of the TinySwitch
topology, while providing a number of new enhancements to
further reduce system cost and component count, and to
practically eliminate audible noise. Like TinySwitch, a 700 V
power MOSFET, oscillator, high voltage switched current source,
current limit and thermal shutdown circuitry are integrated 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
PI-2684-101700
Wide-Range
HV DC Input
D
S
EN/UV
BP
+
-
+
-
DC Output
TinySwitch-II
Optional
UV Resistor
July 2001
PRODUCT
(3)
Adapter
(1)
Open
Frame
(2)
Open
Frame
(2)
OUTPUT POWER TABLE
Table 1. Notes: 1. Typical continuous power in a non-ventilated enclosed
adapter measured at 50 C ambient. 2. Maximum practical continuous
power in an open frame design with adequate heat sinking, measured at
50 C ambient (See key applications section for details). 3. Packages:
P: DIP-8B, G: SMD-8B. Please see part ordering information.
230 VAC
15%
Adapter
(1)
85-265 VAC
5.5 W
9 W
4 W
6 W
10 W
15 W
6 W
9.5 W
13 W
19 W
8 W
12 W
16 W
23 W
10 W
15 W
TNY264P or G
TNY266P or G
TNY267P or G
TNY268P or G
TinySwitch-II devices incorporate auto-restart, line under-
voltage 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
under-voltage 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.
2
B
7/01
TNY264/266-268
Figure 2. Functional Block Diagram.
Figure 3. Pin Configuration.
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
F external bypass capacitor for the
internally generated 5.8 V supply.
ENABLE/UNDER-VOLTAGE (EN/UV) Pin:
This pin has dual functions: enable input and line under-voltage
sense. During normal operation, switching of the power
MOSFET is controlled by this pin. MOSFET switching is
terminated when a current greater than 240
A is drawn from
this pin. This pin also senses line under-voltage 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 under-
voltage function.
SOURCE (S) Pin:
Control circuit common, internally connected to output
MOSFET source.
SOURCE (HV RTN) Pin:
Output MOSFET source connection for high voltage return.
PI-2643-030701
CLOCK
OSCILLATOR
5.8 V
4.8 V
SOURCE
(S)
S
R
Q
DCMAX
BYPASS
(BP)
+
-
VI
LIMIT
FAULT
PRESENT
CURRENT LIMIT
COMPARATOR
ENABLE
LEADING
EDGE
BLANKING
THERMAL
SHUTDOWN
+
-
DRAIN
(D)
REGULATOR
5.8 V
BYPASS PIN
UNDER-VOLTAGE
1.0 V + VT
ENABLE/
UNDER-
VOLTAGE
(EN/UV)
Q
240
A
50
A
LINE UNDER-VOLTAGE
RESET
AUTO-
RESTART
COUNTER
JITTER
1.0 V
6.3 V
CURRENT
LIMIT STATE
MACHINE
PI-2685-101600
EN/UV
D
S
S
S (HV RTN)
S (HV RTN)
BP
P Package (DIP-8B)
G Package (SMD-8B)
8
5
7
1
4
2
3
3
B
7/01
TNY264/266-268
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 Under-Voltage Circuit, Over
Temperature Protection, Current Limit Circuit, Leading Edge
Blanking and a 700 V power MOSFET. TinySwitch-II
incorporates additional circuitry for Line Under-Voltage 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 Figure4
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
A. When the
current out of this pin exceeds 240
A, 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
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
F
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 Under-Voltage
The BYPASS pin under-voltage 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.
Figure 4. Frequency Jitter.
PI-2741-041901
0
5
10
Time (
s)
0
100
200
400
500
600
300
V
DRAIN
136 kHz
128 kHz
4
B
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TNY264/266-268
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 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 under-voltage 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 under-voltage condition, the switching of
the power MOSFET is disabled beyond its normal 850 ms time
until the line under-voltage condition ends.
Line Under-Voltage 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 50
A to initiate switching of the power MOSFET.
During power-up, this is implemented by holding the BYPASS
pin to 4.8 V while the line under-voltage condition exists. The
BYPASS pin then rises from 4.8 V to 5.8V when the line under-
voltage condition goes away. When the switching of the power
MOSFET is disabled in auto-restart mode and a line under-
voltage condition exists, the auto-restart counter is stopped.
This stretches the disable time beyond its normal 850ms until
the line under-voltage condition ends.
The line under-voltage circuit also detects when there is no
external resistor connected to the EN/UV pin (less than ~ 2
A
into pin). In this case the line under-voltage 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. As 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 switch 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
isconnected to the EN/UV pin and the emitter is connected to
Figure 5. TinySwitch-II Auto-Restart Operation.
PI-2699-030701
0
1000
2000
Time (ms)
0
5
0
10
100
200
300
V
DRAIN
V
DC-OUTPUT
5
B
7/01
TNY264/266-268
V
DRAIN
V
EN
CLOCK
D
DRAIN
I
MAX
PI-2749-050301
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
the appropriate current limit. At high loads, when the EN/UV
pin is high (less than 240
A 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 (Figure8). 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
F 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 M
) 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
Figure 6. TinySwitch-II Operation at Near Maximum Loading.
V
DRAIN
V
EN
CLOCK
D
DRAIN
I
MAX
PI-2667-090700
Figure 8. TinySwitch-II Operation at Medium Loading.
PI-2377-091100
V
DRAIN
V
EN
CLOCK
D
DRAIN
I
MAX
Figure 7. TinySwitch-II Operation at Moderately Heavy Loading.
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