Obsolete Product – Not Recommended for New Designs
TNY375-380
TinySwitch-PK
Family
®
Energy-Efficient, Off-Line Switcher With
Enhanced Peak Power Performance
Product Highlights
Lowest System Cost with Enhanced Flexibility
•
Simple ON/OFF control, no loop compensation needed
•
Unique Peak Mode feature extends power range without
increasing transformer size
•
Maximum frequency and current limit boosted at peak loads
•
Selectable current limit through BP/M capacitor value
•
Higher current limit extends maximum power in open frame
•
Lower current limit improves efficiency in enclosed adapters
•
Allows optimum TinySwitch-PK choice by swapping devices
with no other circuit redesign
•
Tight I
2
f parameter tolerance reduces system cost
•
Maximizes MOSFET and magnetics power delivery
•
ON time extension – typically extends low line regulation range/
hold-up time to reduce input bulk capacitance
•
Self-biased: no bias winding required for TNY375-376; winding
required for TNY377-380
•
Frequency jittering reduces EMI filter costs
•
Optimized pin out eases pcb/external heat sinking
•
Quiet source-connected heat sink pins for low EMI
Enhanced Safety and Reliability Features
•
Accurate hysteretic thermal shutdown with automatic recovery
provides complete system level overload protection and
eliminates need for manual reset
•
Auto-restart delivers <3% maximum power in short circuit and
open loop fault conditions
•
Output overvoltage shutdown with optional Zener
•
Line undervoltage detect threshold set using a single resistor
•
Very low component count enhances reliability and enables
single sided printed circuit board layout
•
High bandwidth provides fast turn on with no overshoot and
excellent transient load response
•
Extended creepage between DRAIN and all other pins improves
field reliability
EcoSmart – Extremely Energy Efficient
•
Easily meets all global energy efficiency regulations
•
No-load <170 mW at 265 VAC without bias winding, <60 mW
with bias winding
•
ON/OFF control provides constant efficiency down to very light
loads – ideal for mandatory CEC efficiency regulations and 1 W
PC standby requirements
Applications
•
Applications with high peak-to-continuous power demands –
DVDs, PVRs, active speakers (e.g. PC audio), audio amplifiers,
modems, photo printers
•
Applications with high power demands at startup (large output
capacitance or motor loads) – PC standby, low voltage motor
drives
www.powerint.com
®
AC
IN
+
DC
OUT
D
EN/UV
BP/M
TinySwitch-PK
S
PI-4266-012009
Figure 1.
Typical Peak Power Application.
Output Power Table
230 VAC ± 15%
Product
3
85-265 VAC
Open
Frame
2
15 W
18 W
21.5 W
25 W
28.5 W
Peak
Adapter
1
8.5 W
10 W
13 W
16 W
18 W
20 W
Open
Frame
2
15 W
19 W
23.5 W
28 W
32 W
36.5 W
Peak Adapter
1
16.5 W
22 W
28 W
34 W
39 W
45 W
6W
7W
8W
10 W
12 W
14 W
TNY375P/G/D
4
TNY376P/G/D
4
TNY377P/G
TNY378P/G
TNY379P/G
TNY380P/G
11.5 W 12.5 W
17 W
23 W
27 W
31 W
35 W
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at +50 °C ambient. Use of an external heat sink will increase power
capability.
2. Minimum continuous power in an open frame design (see Key Applications
Considerations).
3. Packages: P: DIP-8C, G: SMD-8C, D: SO-8C. Lead free only. See Part Ordering
Information.
4. See Key Application Considerations.
Description
TinySwitch-PK incorporates a 700 V MOSFET, oscillator, high-
voltage switched current source, current limit (user selectable),
and thermal shutdown circuitry. A unique peak mode feature
boosts current limit and frequency for peak load conditions. The
boosted current limit provides the peak output power while the
increased peak mode frequency ensures the transformer can be
sized for continuous load conditions rather than peak power
demands.
September 2012
TNY375-380
BYPASS/
MULTI-FUNCTION
(BP/M)
REGULATOR
5.85 V
25 A
LINE UNDER-VOLTAGE
FAULT
PRESENT
AUTO-
RESTART
COUNTER
RESET
+
DRAIN
(D)
115 A
BYPASS PIN
UNDER-VOLTAGE
V
I
BYPASS
-
CAPACITOR
5.85 V
SELECT AND
4.9 V
CURRENT
LIMIT STATE
MACHINE
LIMIT
ENABLE
CURRENT LIMIT
COMPARATOR
-
+
1.0 V + V
T
JITTER 2X
CLOCK
DCMAX
OSCILLATOR
THERMAL
SHUTDOWN
ENABLE/
UNDER-
VOLTAGE
(EN/UV)
1.0 V
6.4 V
OVP
LATCH
RESET
S
Q
R
Q
LEADING
EDGE
BLANKING
SOURCE
(S)
PI-4550-121406
Figure 2
Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
This pin is the power MOSFET drain connection. It provides
internal operating current for both start-up and steady-state
operation.
BYPASS/MULTI-FUNCTION (BP/M) Pin:
This pin has multiple functions:
1. It is the connection point for an external bypass capacitor for
the internally generated 5.85 V supply.
2. It is a mode selector for the current limit value, depending on
the value of the capacitance added. Use of a 0.1
mF
capacitor results in the standard current limit value. Use of a
1
mF
capacitor results in the current limit being reduced to
that of the next smaller device size. Use of a 10
mF
capacitor
results in the current limit being increased to that of the next
larger device.
3. It provides a shutdown function. When the current into the
bypass pin exceeds 7 mA, the device latches off until the
BP/M voltage drops below 4.9 V, during a power down or
when a line undervoltage is detected. This can be used to
provide an output overvoltage function with a Zener diode
connected from the BP/M pin to a bias winding supply.
P Package (DIP-8C)
G Package (SMD-8C)
D Package (SO-8C)
EN/UV
BP/M
1
2
8
7
6
S
S
S
S
D
4
5
PI-4348-042809
Figure 3.
Pin Configuration.
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 a threshold current is
drawn from this pin. Switching resumes when the current being
2
Rev. C 09/12
www.powerint.com
TNY375-380
pulled from the pin drops to less than a threshold current. A
modulation of the threshold current reduces group pulsing. The
threshold current is between 75
mA
and 115
mA.
The EN/UV 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-PK detects its absence and disables the line under-
voltage function.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high voltage power return and control circuit common.
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 with an oscillator frequency of 264 kHz.
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 1.2 V. The current
through the source follower is limited to 115
mA.
When the
current out of this pin exceeds the threshold current, a low logic
level (disable) is generated at the output of the enable circuit
until the current out of this pin is reduced to less than the
threshold current. 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. When a cycle is
disabled, the EN/UV pin is sampled at 264 kHz. This faster
sampling enables the power supply to respond faster without
being required to wait for completion of the full period.
The current limit state machine reduces the current limit by
discrete amounts at light loads when TinySwitch-PK 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 enable events 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 1.2 V in the
disabled state. This improves the response time of the
optocoupler that is usually connected to this pin.
5.85 V Regulator and 6.4 V Shunt Voltage Clamp
The 5.85 V regulator charges the bypass capacitor connected
to the BYPASS pin to 5.85 V by drawing a current from the
voltage on the DRAIN pin whenever the MOSFET is off. The
BYPASS/MULTI-FUNCTION pin is the internal supply voltage
node. When the MOSFET is on, the device operates from the
energy stored in the bypass capacitor. Extremely low power
consumption of the internal circuitry allows the TNY375 and
TNY376 to operate continuously from current taken from the
DRAIN pin. A bypass capacitor value of 0.1
mF
is sufficient for
both high frequency decoupling and energy storage.
In addition, there is a 6.4 V shunt regulator clamping the
BYPASS/MULTI-FUNCTION pin at 6.4 V when current is provided
to the BYPASS/MULTI-FUNCTION pin through an external
resistor. This facilitates powering of TinySwitch-PK externally
through a bias winding as required for TNY377-380. Powering
the TinySwitch-PK externally in this way also decreases the
no-load consumption to below 60 mW.
TinySwitch-PK Functional Description
TinySwitch-PK combines a high voltage power MOSFET switch
with a power supply controller in one device. Unlike conventional
PWM (pulse width modulator) controllers, it uses a simple ON/
OFF control to regulate the output voltage.
The controller consists of an oscillator, enable circuit (sense and
logic), current limit state machine, 5.85 V regulator, BYPASS/
MULTI-FUNCTION pin undervoltage, overvoltage circuit, and
current limit selection circuitry, over-temperature protection,
current limit circuit, leading edge blanking, and a 700 V power
MOSFET. TinySwitch-PK incorporates additional circuitry for line
undervoltage sense, auto-restart, adaptive switching cycle
on-time extension, 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
264 kHz (at the highest current limit level). 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 oscillator incorporates circuitry that introduces a small
amount of frequency jitter, typically
±3%
of the oscillator
frequency, to minimize EMI emission. The modulation rate of the
PI-4539-102207
600
500
V
DRAIN
400
300
200
100
0
280 kHz
248 kHz
0
Figure 4.
Frequency Jitter.
2.5
5
Time (µs)
3
www.powerint.com
Rev. C 09/12
TNY375-380
BYPASS/MULTI-FUNCTION Pin Undervoltage
The BYPASS/MULTI-FUNCTION pin undervoltage circuitry
disables the power MOSFET when the BYPASS/MULTI-
FUNCTION pin voltage drops below 4.9 V in steady state
operation. Once the BYPASS/MULTI-FUNCTION pin voltage
drops below 4.9 V in steady state operation, it must rise back to
5.85 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 142 °C with 75 °C hysteresis.
When the die temperature rises above this threshold, the power
MOSFET is disabled and remains disabled, until the die
temperature falls by 75 °C, at which point it is re-enabled. A
large hysteresis of 75 °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 typical 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-PK enters
into auto-restart operation. An internal counter clocked by the
oscillator is reset every time the EN/UV pin is pulled low. If the
EN/UV pin is not pulled low for 8192 switching cycles
(or 32 ms), the power MOSFET switching is normally disabled
for 1 second (except in the case of line undervoltage condition,
in which case it is disabled until the condition is removed). The
PI-4320-030106
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 1 second
until the line undervoltage condition ends.
Adaptive Switching Cycle On-Time Extension
Adaptive switching cycle on-time extension keeps the cycle on
until current limit is reached, instead of prematurely terminating
after the DC
MAX
signal goes low. This feature reduces the
minimum input voltage required to maintain regulation, typically
extending hold-up time and minimizing the size of bulk
capacitor required. The on-time extension is disabled during
the startup of the power supply, and after auto-restart, until the
power supply output reaches regulation.
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 25
mA
to initiate switching of the power MOSFET.
During power-up, this is accomplished by holding the BYPASS/
MULTI-FUNCTION pin to 4.9 V while the line undervoltage
condition exists. After the line undervoltage condition goes
away and the BYPASS/MULTI-FUNCTION pin has stabilized at
5.85 V, switching is initiated. Once MOSFET switching is
enabled, the DC line voltage is ignored unless the power supply
enters auto-restart mode in the event of a fault condition. 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 1 second 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 ~1
mA
into the pin). In this case the line undervoltage function is
disabled.
TinySwitch-PK Operation
TinySwitch-PK 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 (applicable when On-Time Extension is disabled).
Since the highest current limit level and frequency of a
TinySwitch-PK 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-PK 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.
300
200
100
0
10
V
V
DRAIN
5
0
DC-OUTPUT
0
Figure 5.
Auto-Restart Operation.
1000
2000
Time (ms)
4
Rev. C 09/12
www.powerint.com
TNY375-380
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-PK runs at all times. 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, the state machine
sets the current limit to its highest value. With TinySwitch-PK,
when the state machine sets the current limit to its highest
value, the oscillator frequency is also doubled, providing the
unique peak mode operation. At lighter loads, the state
machine sets the current limit to reduced values. At these lower
current limit levels, the oscillator frequency returns to the
standard value.
At near maximum load, TinySwitch-PK 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, more cycles will be skipped, the current limit will be
V
EN
CLOCK
DC
MAX
I DRAIN
V DRAIN
PI-2749-082305
Figure 6.
Operation at Near Maximum Loading (f
OSC
264 kHz).
V
EN
CLOCK
DC
MAX
I DRAIN
V
EN
CLOCK
V DRAIN
DC
MAX
PI-2667-082305
Figure 7.
Operation at Moderately Heavy Loading (f
OSC
264 kHz).
I DRAIN
Enable Function
TinySwitch-PK senses the EN/UV pin to determine whether or
not to proceed with the next switching cycle. 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 halfway 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.
V DRAIN
PI-4540-050407
Figure 8.
Operation at Medium Loading (f
OSC
132 kHz).
5
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Rev. C 09/12
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