TNY174-180
TinySwitch-LT
Family
Energy Efficient, Offline Switcher with Enhanced
Flexibility and Extended Power Range
Product Highlights
Lowest System Cost with Enhanced Flexibility
•
650 V rating optimized for non-active PFC applications
•
Simple ON/OFF control, no loop compensation needed
•
Selectable current limit through BP/M capacitor value
•
Higher current limit extends peak power or, in open frame
AC
Input
+
DC
Output
•
•
•
•
•
•
applications, maximum continuous power
•
Lower current limit improves efficiency in enclosed adapters/
chargers
•
Allows optimum TinySwitch-LT choice by swapping
devices with no other circuit redesign
Tight I
2
f parameter tolerance reduces system cost
•
Maximizes MOSFET and magnetics power delivery
•
Minimizes max overload power, reducing cost of
transformer, primary clamp & secondary components
ON-time extension – extends low-line regulation range/hold-up time
to reduce input bulk capacitance
Self-biased: no bias winding or bias components
Frequency jittering reduces EMI filter costs
Pin-out simplifies heat sinking to the PCB
SOURCE pins are electrically quiet for low EMI
D
EN
BP/M
TinySwitch-LT
S
PI-4770-010709
Figure 1. Typical Application.
Output Power Table
230 VAC ± 15%
Product
3
TNY174P/D
4
TNY175P/D
TNY177P
4
TNY177D
TNY178P
TNY178D
TNY179P
TNY180P
4
85-265 VAC
Adapter
1
5W
6W
7W
8W
7W
10 W
9W
12 W
14 W
Peak or
Open
Frame
2
8.5 W
11.5 W
15 W
18 W
18 W
21.5 W
19.5 W
25 W
28.5 W
Adapter
1
6W
8.5 W
10 W
13 W
11.5 W
16 W
14.5 W
18 W
20 W
Enhanced Safety and Reliability Features
•
Accurate hysteretic thermal shutdown protection with
automatic recovery eliminates need for manual reset
•
Auto-restart delivers <3% of maximum power in short-circuit and
open loop fault conditions
•
Output overvoltage shutdown with optional Zener
•
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
Peak or
Open
Frame
2
11 W
15 W
19 W
23.5 W
23.5 W
28 W
26 W
32 W
36.5 W
TNY176P/D
4
EcoSmart
– Extremely Energy Efficient
™
•
Easily meets all global energy efficiency regulations
•
No-load <150 mW at 265 VAC without bias winding,
•
ON/OFF control provides constant efficiency down to very light loads
<50 mW with bias winding
– ideal for mandatory CEC regulations
Applications
•
Chargers/adapters for cell/cordless phones, PDAs, digital cameras,
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 peak power capability in any design or minimum continuous power
in an open frame design (see Key Applications Considerations).
3. Packages: P: DIP-8C, D: SO-8C. See Part Ordering Information.
4. See Key Application Considerations.
MP3/portable audio, shavers, etc.
•
DVD/PVR and other low power set top decoders
•
Supplies for appliances, industrial systems, metering, etc.
Description
TinySwitch™-LT incorporates a 650 V power MOSFET, oscillator,
high-voltage switched current source, current limit (user selectable) and
thermal shutdown circuitry. The IC family uses an ON/OFF control
scheme and offers a design flexible solution with a low system cost and
extended power capability.
www.power.com
August 2016
TNY174-180
BYPASS/
MULTI-FUNCTION
(BP/M)
REGULATOR
5.85 V
DRAIN
(D)
115
µA
AUTO-
RESTART
COUNTER
RESET
FAULT
PRESENT
+
BYPASS PIN
UNDER-VOLTAGE
BYPASS
-
CAPACITOR
SELECT AND 5.85 V
4.9 V
CURRENT
LIMIT STATE
MACHINE
V
I
LIMIT
CURRENT LIMIT
COMPARATOR
ENABLE
-
+
JITTER
CLOCK
1.0 V + V
T
ENABLE
(EN)
1.0 V
DCMAX
OSCILLATOR
S
Q
THERMAL
SHUTDOWN
R
Q
OVP
LATCH
LEADING
EDGE
BLANKING
SOURCE
(S)
PI-4771-090313
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 size
for TNY175-180.
3.
It provides a shutdown function. When the current into the
bypass pin exceeds I
SD
, the device latches off until the
BP/M voltage drops below 4.9 V, during a power-down. This can
be used to provide an output overvoltage function with a Zener
connected from the BP/M pin to a bias winding supply.
P Package (DIP-8C)
EN
BP/M
1
2
8
7
6
S
S
S
S
D Package (SO-8C)
EN 1
8S
7S
6S
D4
5S
PI-4772-090313
D
4
5
BP/M 2
Figure 3. Pin Configuration.
2
Rev. G 08/16
www.power.com
TNY174-180
ENABLE (EN) Pin:
The 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 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.
Enable Input and Current Limit State Machine
The enable input circuit at the ENABLE pin consists of a low imped-
ance 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 ENABLE 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-LT 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 transform-
er 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
ENABLE 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-FUNC-
TION 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 TinySwitch-LT to operate continuously from current it takes
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-LT externally through a bias
winding to decrease the no-load consumption to well below 50 mW.
BYPASS/MULTI-FUNCTION Pin
The BYPASS/MULTI-FUNCTION pin 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 over-heating of the PC board due to a continuous fault
condition.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high-voltage power return and control circuit common.
TinySwitch-LT Functional Description
TinySwitch-LT 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 , overvoltage circuit, and current limit selection
circuitry, over-temperature protection, current limit circuit, leading
edge blanking, and a 650 V power MOSFET. TinySwitch-LT incorpo-
rates additional circuitry for auto-restart, adaptive switching cycle
on-time extension, and frequency jitter. Figure 2 shows the func-
tional 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 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.
600
500
V
DRAIN
400
300
200
100
0
136 kHz
128 kHz
0
5
Time (µs)
10
Figure 4. Frequency Jitter.
PI-2741-041901
3
www.power.com
Rev. G 08/16
TNY174-180
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-LT enters into
auto-restart operation. An internal counter clocked by the oscillator
is reset every time the ENABLE pin is pulled low. If the ENABLE pin is
not pulled low for 64 ms, the power MOSFET switching is normally
disabled for 2.5 seconds. 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 pres-
ence of an output short-circuit.
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, extending hold-up time and
minimizing the size of bulk capacitor required. The on-time extension
is disabled during the start-up of the power supply, until the power
supply output reaches regulation.
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-LT 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-LT senses the ENABLE 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 ENABLE 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 ENABLE pin signal is generated on the secondary by comparing
the power supply output voltage with a reference voltage. The
ENABLE pin signal is high when the power supply output voltage is
less than the reference voltage.
In a typical implementation, the ENABLE pin is driven by an
optocoupler. The collector of the optocoupler transistor is connected
to the ENABLE 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 ENABLE 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-LT runs all the time. At the
beginning of each clock cycle, it samples the ENABLE pin to decide
whether or not to implement a switch cycle, and based on the
sequence of samples over multiple cycles, it determines the appropri-
ate current limit. At high loads, the state machine sets the current
limit to its highest value. At lighter loads, the state machine sets the
current limit to reduced values.
At near maximum load, TinySwitch-LT 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 ON/OFF control scheme is very fast
compared to PWM control. This provides tight regulation and
excellent transient response.
Power-Up/Down
The TinySwitch-LT requires only a 0.1
mF
capacitor on the BYPASS/
MULTI-FUNCTION pin to operate with standard current limit.
Because of its small size, the time to charge this capacitor is kept to
an absolute minimum, typically 0.6 ms. The time to charge will vary
in proportion to the BYPASS/MULTI-FUNCTION pin capacitor value
when selecting different current limits. Due to the high bandwidth of
the ON/OFF feedback, there is no overshoot at the power supply
output.
Figure 10 shows typical power-up timing waveforms.
TinySwitch-LT Operation
TinySwitch-LT 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-LT design
are constant, the power delivered to the load is proportional to the
300
200
100
0
10
V
V
DRAIN
5
0
DC-OUTPUT
0
Figure 5. Auto-Restart Operation.
2500
5000
Time (ms)
4
Rev. G 08/16
PI-4098-082305
www.power.com
TNY174-180
Under start-up and overload conditions, when the conduction time is
less than 400 ns, the device reduces the switching frequency to main-
tain control of the peak drain current.
During power-down, the power MOSFET will switch for 64 ms after
the output loses regulation.
Figure 11 illustrates a typical power-down timing waveform.
No bias winding is needed to provide power to the chip because it
draws the power directly from the DRAIN pin (see Functional
Description above). This has two main benefits. First, for a nominal
application, this eliminates the cost of a bias winding and associated
components. Secondly, for battery charger applications, the
current-voltage characteristic often allows the output voltage to fall
close to zero volts while still delivering power. TinySwitch-LT
accomplishes this without a forward bias winding and its many associ-
ated components. For applications that require very low no-load
power consumption (50 mW), a resistor from a bias winding to the
BYPASS/MULTI-FUNCTION pin can provide the power to the chip.
The minimum recommended current supplied is 1 mA. The BYPASS/
MULTI-FUNCTION pin in this case will be clamped at 6.4 V. This
method will eliminate the power draw from the DRAIN pin, thereby
reducing the no-load power consumption and improving full-load
efficiency.
Current Limit Operation
Each switching cycle is terminated when the DRAIN current reaches
the current limit of the device. Current limit operation provides good
line ripple rejection and relatively constant power delivery indepen-
dent of input voltage.
BYPASS/MULTI-FUNCTION Pin Capacitor
The BYPASS/MULTI-FUNCTION pin can use a ceramic capacitor as
small as 0.1
mF
for decoupling the internal power supply of the
device. A larger capacitor size can be used to adjust the current limit.
For TNY175-180, a 1
mF
BP/M pin capacitor will select a lower current
limit equal to the standard current limit of the next smaller device and
a 10
mF
BP/M pin capacitor will select a higher current limit equal to
the standard current limit of the next larger device. The higher
current limit level of the TNY180 is set to 850 mA typical. The
TNY174 MOSFET does not have the capability for increased current
limit so this feature is not available in this device.
V
EN
CLOCK
DC
MAX
I DRAIN
V DRAIN
PI-2749-082305
Figure 6. Operation at Near Maximum Loading.
V
EN
CLOCK
DC
V
EN
CLOCK
DC
MAX
MAX
IDRAIN
I DRAIN
VDRAIN
V DRAIN
PI-2667-082305
PI-2377-082305
Figure 7. Operation at Moderately Heavy Loading.
Figure 8. Operation at Medium Loading.
5
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Rev. G 08/16
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