ETC LD7536

LD7536
11/8/2010
Green-Mode PWM Controller with Frequency Swapping
and Integrated Protections
Rev. 01
General Description
Features
The LD7536 is built-in with several functions, protection
z
and EMI-improved solution in a tiny package. It takes less
High-Voltage CMOS Process with Excellent ESD
protection
components counts or circuit space, especially ideal for
z
Very Low Startup Current (<20μA)
those total solutions of low cost.
z
Current Mode Control
z
Green Mode Control
z
UVLO (Under Voltage Lockout)
z
LEB (Leading-Edge Blanking) on CS Pin
z
Internal Frequency Swapping
z
Internal Slope Compensation
z
OVP (Over Voltage Protection) on Vcc Pin
z
OTP (Over Temperature Protection) through a NTC
z
OLP (Over Load Protection)
z
300mA Driving Capability
The implemented functions include low startup current,
green-mode
power-saving
operation,
leading-edge
blanking of the current sensing and internal slope
compensation.
It also features more protections like
OLP (Over Load Protection) and OVP (Over Voltage
Protection) to prevent circuit damage occurred under
abnormal conditions.
Furthermore, the Frequency Swapping function is to
reduce the noise level and thus helps the power circuit
designers to easily deal with the EMI filter design by
Applications
spending minimum amount of component cost and
z
Switching AC/DC Adaptor and Battery Charger
developing time.
z
Open Frame Switching Power Supply
Typical Application
1
Leadtrend Technology Corporation
LD7536-DS-01 APD
November 2010
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LD7536
Pin Configuration
SOT-26 (TOP VIEW)
COMP
NC
8
7
6
OTP
GND
DIP-8 (TOP VIEW)
OUT
VCC
5
6
5
36
YWP pp
1
2
TOP MARK
1
2
3
4
OUT
VCC
NC
CS
YYWWPP
GND
YY, Y
WW, W
PP
P36
Ordering Information
Part number
CS
4
3
COMP OTP
: Year code (D: 2004, E: 2005…..)
: Week code
: Production code
: LD7536
Package
Top Mark
Shipping
LD7536 GL
SOT-26
Green Package
YWP/36
3000 /tape & reel
LD7536 GN
DIP-8
Green Package
LD7536 GN
3600 /tube /Carton
Protection Mode
Switching Freq.
VCC OVP
OLP
OTP Pin
65kHz
Latch
Auto recovery/ 65ms
Latch
Pin Descriptions
PIN
PIN
SOT-26
DIP-8
1
8
GND
2
7
COMP
NAME
FUNCTION
Ground
Voltage feedback pin (same as the COMP pin in UC384X). Connect a
photo-coupler to close the control loop and achieve the regulation.
Pull this pin below 0.95V to shutdown the controller into latch mode until the AC
3
5
OTP
resume power-on. Connecting this pin to ground with NTC will achieve OTP
protection. Keep this pin float to disable the latch protection.
4
4
CS
Current sense pin, connect it to sense the MOSFET current
5
2
VCC
Supply voltage pin
6
1
OUT
Gate drive output to drive the external MOSFET
2
Leadtrend Technology Corporation
LD7536-DS-01 APD
November 2010
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LD7536
Block Diagram
∑
3
Leadtrend Technology Corporation
LD7536-DS-01 APD
November 2010
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LD7536
Absolute Maximum Ratings
Supply Voltage VCC
-0.3V ~29V
COMP, RT, CS
-0.3V ~6V
OUT
-0.3V ~Vcc+0.3V
Maximum Junction Temperature
150°C
Operating Ambient Temperature
-20°C to 85°C
Operating Junction Temperature
-40°C to 125°C
Storage Temperature Range
-65°C to 150°C
Package Thermal Resistance (SOT-26, θJA)
250°C/W
Package Thermal Resistance (DIP-8, θJA)
100°C/W
Power Dissipation (SOT-26, at Ambient Temperature = 85°C)
250mW
Power Dissipation (DIP-8, at Ambient Temperature = 85°C)
650mW
Lead temperature (Soldering, 10sec)
260°C
ESD Voltage Protection, Human Body Model
2.5 KV
ESD Voltage Protection, Machine Model
250 V
Gate Output Current
300mA
Caution:
Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only
rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification
is not implied.
Recommended Operating Conditions
Item
Supply Voltage Vcc
Start-up resistor Value
Min.
Max.
Unit
11
24
V
540K
1.8 M
Ω
4
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LD7536-DS-01 APD
November 2010
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LD7536
Electrical Characteristics
(TA = +25°C unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
12
20
μA
Supply Voltage (Vcc Pin)
Startup Current
Operating Current
(with 1nF load on OUT pin)
Holding Current
VCOMP=0V
1.0
mA
VCOMP=3V
2.0
mA
OLP Tripped/ Auto
0.4
mA
OVP Tripped/Latch
0.85
mA
OTP Pin Tripped/Latch
0.85
mA
Vcc=7V (latched)
430
μA
UVLO (off)
9
10
11
V
UVLO (on)
15
16
17
V
OVP Level
25
26
27
V
Voltage Feedback (Comp Pin)
Short Circuit Current
VCOMP=0V
0.25
mA
Open Loop Voltage
COMP pin open
5.4
V
Green Mode Threshold VCOMP
2.2
V
Zero Duty Threshold VCOMP
1.4
V
Zero Duty Hysteresis
100
mV
Current Sensing (CS Pin)
Maximum Input Voltage, VCS_OFF
0.8
Leading Edge Blanking Time
Internal Slope Compensation
0% to DMAX. (Linearly increase)
Input impedance
0.85
0.9
230
ns
300
mV
1
Delay to Output
V
MΩ
100
ns
Oscillator for Switching Frequency
Frequency, FREQ
60
Green Mode Frequency, FREQG
Trembling Frequency
Temp. Stability
(-20°C ~85°C)
Voltage Stability
(VCC=11V-25V)
5
Leadtrend Technology Corporation
LD7536-DS-01 APD
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65
70
kHz
22
kHz
± 4.0
kHz
5
%
1
%
LD7536
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1
V
Gate Drive Output (OUT Pin)
Output Low Level
VCC=15V, Io=20mA
Output High Level
VCC=15V, Io=20mA
8
Rising Time
Load Capacitance=1000pF
--
Falling Time
Load Capacitance=1000pF
Max. Duty
V
170
350
ns
50
100
ns
75
%
OLP (Over Load Protection)
OLP Trip Level
4.3
4.5
4.7
65
OLP Delay Time
V
ms
OTP Pin Latch Protection (OTP Pin)
77
85
92
μA
Turn-On Trip Level
1.00
1.05
1.10
V
Turn-Off Trip Level
0.9
0.95
1.0
V
OTP Pin Source Current
250
μs
OTP Level
140
°C
OTP Hysteresis
30
°C
2
ms
OTP pin de-bounce time
On Chip OTP (Over Temperature)
Soft Start Duration
Soft Start Duration
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LD7536-DS-01 APD
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LD7536
18.0
12
17.2
11.2
UVLO (off) (V)
UVLO (on) (V)
Typical Performance Characteristics
16.4
15.6
8
-40
0
40
Fig. 1
80
120 125
-40
Fig. 2
120
125
UVLO (off ) vs. Temperature
26
Green Mode Frequency (KHz)
66
64
62
60
-40
0
40
80
24
22
20
18
16
120 125
-40
0
40
80
120 125
Temperature (°C)
Temperature (°C)
Fig. 3 Frequency vs. Temperature
Fig. 4 Green Mode Frequency vs. Temperature
25
Green Mode Frequency (KHz)
70
68
Frequency (KHz)
80
40
Temperature (°C)
68
66
64
62
60
11
0
Temperature (°C)
UVLO (on) vs. Temperature
70
Frequency (KHz)
9.6
8.8
14.8
14.0
10.4
12
14
16
18
20
22
24
November 2010
17
12
14
16
18
20
22
Fig. 6 Green Mode Frequency vs. Vcc
7
LD7536-DS-01 APD
19
Vcc (V)
Frequency vs. Vcc
Leadtrend Technology Corporation
21
15
11
25
Vcc (V)
Fig. 5
23
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24
25
85
0.90
80
0.88
VCS (off) (V)
Max Duty (%)
LD7536
75
70
0.86
0.84
0.82
65
60
-40
0
40
80
0.80
-40
120 125
Temperature (°C)
Fig. 7
s
te
VCC OVP (V)
Istartup (μA)
120 125
30
12
9
6
25
20
15
3
0
-40
0
Fig. 9
40
80
10
120 125
-40
0
40
80
Temperature (°C)
Temperature (°C)
Startup Current (Istartup) vs. Temperature
Fig. 10 VCC OVP vs. Temperature
6.5
6.0
6.0
5.0
5.5
4.5
OLP (V)
VCOMP (V)
80
35
15
5.0
4.5
4.0
40
Temperature (°C)
Fig. 8 VCS (off) vs. Temperature
Max Duty vs. Temperature
18
0
120
125
4.0
3.5
-40
0
40
80
3.0
120 125
-40
Temperature (°C)
8
LD7536-DS-01 APD November 2010
40
80
Temperature (°C)
Fig. 12 OLP-Trip Level vs. Temperature
Fig. 11 VCOMP open loop voltage vs. Temperature
Leadtrend Technology Corporation
0
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120 125
LD7536
Application Information
Operation Overview
current. Lower startup current requirement on the PWM
The LD7536 meets the green-power requirement and is
controller will help to increase the value of R1 and then
intended for the use in those modern switching power
reduce the power consumption on R1. By using CMOS
suppliers and adaptors which demand higher power
process and the special circuit design, the maximum
efficiency and power-saving. It integrated more functions
startup current for LD7536 is only 20μA.
to reduce the external components counts and the size.
If a higher resistance value of the R1 is chosen, it will
Its major features are described as below.
usually take more time to start up. To carefully select the
value of R1 and C1 will optimize the power consumption
and startup time.
Under Voltage Lockout (UVLO)
An UVLO comparator is implemented in it to detect the
EMI
Filter
voltage on the VCC pin. It would assure the supply
voltage enough to turn on the LD7536 PWM controller
and further to drive the power MOSFET. As shown in Fig.
13, a hysteresis is built in to prevent the shutdown from
the voltage dip during startup. The turn-on and turn-off
threshold level are set at 16.0V and 10.0V, respectively.
Vcc
UVLO(on)
UVLO(off)
t
I(Vcc)
Fig. 14
operating current
(~ mA)
Current
startup current
(~uA)
Sensing
and
Leading-edge
Blanking
The typical current mode of PWM controller feedbacks
t
both current signal and voltage signal to close the control
Fig. 13
loop and achieve regulation. As shown in Fig. 15, the
Startup Current and Startup Circuit
LD7536 detects the primary MOSFET current from the CS
The typical startup circuit to generate VCC of the LD7536 is
pin, which is not only for the peak current mode control
shown in Fig. 14. During the startup transient, the VCC is
but also for the pulse-by-pulse current limit. The maximum
below UVLO threshold. Before it has sufficient voltage to
voltage threshold of the current sensing pin is set at 0.85V.
develop OUT pulse to drive the power MOSFET, R1 will
From above, the MOSFET peak current can be obtained
provide the startup current to charge the capacitor C1.
from below.
IPEAK(MAX) =
Once VCC obtain enough voltage to turn on the LD7536
and further to deliver the gate drive signal, it will enable
the auxiliary winding of the transformer to provide supply
9
Leadtrend Technology Corporation
LD7536-DS-01 APD November 2010
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0.85 V
RS
LD7536
A pull-high resistor is embedded internally and can be
eliminated externally.
Fig. 15
A 230nS leading-edge blanking (LEB) time is included in
the input of CS pin to prevent the false-trigger from the
current spike. In the low power application, if the total
pulse width of the turn-on spikes is less than 230nS and
the negative spike on the CS pin below -0.3V, the R-C
filter is free to eliminate. (As shown in Fig.16).
However, the total pulse width of the turn-on spike is
determined according to output power, circuit design and
PCB layout.
Fig. 16
It is strongly recommended to adopt a
smaller R-C filter (as shown in Fig. 17) for larger power
application to avoid the CS pin being damaged by the
negative turn-on spike.
Output Stage and Maximum Duty-Cycle
An output stage of a CMOS buffer, with typical 300mA
driving capability, is incorporated to drive a power
MOSFET directly.
And the maximum duty-cycle of
LD7536 is limited to 75% to avoid the transformer
saturation.
Voltage Feedback Loop
The voltage feedback signal is provided from the TL431 at
the secondary side through the photo-coupler to the
COMP pin of the LD7536.
Similar to UC3842, the
LD7536 would carry a diode voltage offset at the stage to
Fig. 17
feed the voltage divider at the ratio of RA and RB, that is,
RB
× ( VCOMP − VF )
V−(PWM COMPARATOR ) =
RA + RB
10
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LD7536
VCC
Internal Slope Compensation
In the conventional applications, the problem of the
UVLO(on)
stability is a critical issue for current mode controlling,
UVLO(off)
when it operates over 50% duty-cycle. As UC384X, It
OLP
takes slope compensation from injecting the ramp signal
of the RT/CT pin through a coupling capacitor. It therefore
UVLO(off)
OLP Reset
t
COMP
OLP delay time
requires no extra design for the LD7536 since it has
integrated it already.
4.5V
OLP trip Level
t
On/Off Control
OUT
The LD7536 can be turned off by pulling COMP pin lower
than 1.4V. The gate output pin of the LD7536 will be
Switching
disabled immediately under such condition. The off-mode
Non-Switching
can be released when the pull-low signal is removed.
Switching
t
Fig. 18
Over
Load
Protection
(OLP)
-
Auto
OVP (Over Voltage Protection) on Vcc -
Recovery
Latch mode
To protect the circuit from damage due to over-load
The Vcc OVP function of LD7536 is in latch mode. As
condition and short or open-loop condition, the LD7536 is
soon as the voltage of the Vcc pin rises above OVP
implemented with smart OLP function. It also features
threshold, the output gate drive circuit will be shutdown
auto recovery function, see Fig. 18 for the waveform. In
simultaneous to latch off the power MOSFET. On the
case of fault condition, the feedback system will force the
contrast, if the voltage on Vcc pin drops below OVP
voltage loop toward the saturation and then pull the
threshold and starts AC-recycling again, it will soon
voltage high on COMP pin (VCOMP). When the VCOMP
resume to normal operation. Fig. 19 shows its operation.
ramps up to the OLP threshold of 4.5V and continues over
OLP delay time, the protection will be activated and then
turn off the gate output to stop the switching of power
circuit.
With the protection mechanism, the average input power
will be minimized to remain the component temperature
and stress within the safe operating area.
Fig. 19
11
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LD7536
OTP Pin --- Latched Mode Protection
Green-Mode Operation
By using the green-mode control, the switching frequency
To protect the power circuit from damage due to system
can be reduced under the light load condition. This feature
failure, over temperature protection (OTP) is required. The
helps to improve the efficiency in light load conditions.
OTP circuit is implemented to sense a hot-spot of power
The green-mode control is Leadtrend Technology’s own
circuit like power MOSFET or output rectifier. It can be
property.
easily achieved by connecting a NTC with OTP pin of
LD7536.
As the device temperature or ambient
Fault Protection
temperature rises, the resistance of NTC decreases. So,
There are several critical protections integrated in the
the voltage on the OTP pin could be written as below.
LD7536 to prevent from damage to the power supply.
VOTP = 85μA ⋅ R NTC
Those damages usually come from open or short
conditions on the pins of LD7536.
When the VOTP is below the defined voltage threshold (typ.
In case under such conditions listed below, the gate
0.95V), LD7536 will shutdown the gate output and latch
output will turn off immediately to protect the power circuit.
off the power supply. There are 2 conditions required to
1.
CS pin floating
restart it successfully. First, cool down the circuit so that
2.
COMP pin floating
NTC resistance will increase and raise VOTP up above
1.05V. Then, remove the AC power cord and restart AC
power-on recycling.
Oscillator and Switching Frequency
The LD536 is implemented with Frequency Swapping
function which helps the power supply designers to both
optimize EMI performance and lower system cost. The
switching frequency substantially centers at 65KHz, and
swap between a range of ±4KHz.
12
Leadtrend Technology Corporation
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LD7536
Reference Application Circuit --- 40W (19V/2.1A) Adapter
R1
2.2MEG/1206
R2
2.2MEG/1206
L2
22mH
CX1
0.22uF
R5
620K/1206
C12
104P/0805
BR1
KBP206
C4
82uF/400V
R6
5 VCC
620K/1206
2 COMP
C5
NC
CS 4
OUT 6
LD7536
GND
1
R9
51K/1206
R10
51k/1206
R12B
C6
102pF/1206
R11
22R/1206
D2
PR1007
D6
D4148
10R/0805
R12
200R/0805
R13
100R/0805
C14
100PF/0805
T1A
RM8
51R/1206
D5
20120
C7
470uF/25V
IC432
R16B
1.4/1206
C1
330P/1206 R3
Q1
2SK3562
R16
1.4/1206
CY1
102P
U1A
SMD
C8
470uF/25V
C10
104P/0805
DZ2/6.8V
+Vo
19V / 2.1A
RTN
R28
62K/0805
R30
/0805
C16
473p/0805
ZENER1
R32
5.6k/0805
R31
330/0805
R25
1K/0805
R29
4.3k/0805
13
F1
L1
3.15A/250V 120uH
L
N
C11
4.7u/50V
D1
R4
0/0805 GS1002FL
T1B
PC817B
3.3nF/0805
C13
3 OTP
C13
100P/0805
R16A
1.4/1206
LD7536-DS-01 APD November 2010
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Leadtrend Technology Corporation
LD7536
Package Information
SOT-26
Symbol
Dimension in Millimeters
Dimensions in Inches
Min
Max
Min
Max
A
2.692
3.099
0.106
0.122
B
1.397
1.803
0.055
0.071
C
-------
1.450
-------
0.057
D
0.300
0.500
0.012
0.020
F
0.95 TYP
0.037 TYP
H
0.080
0.254
0.003
0.010
I
0.050
0.150
0.002
0.006
J
2.600
3.000
0.102
0.118
M
0.300
0.600
0.012
0.024
θ
0°
10°
0°
10°
14
Leadtrend Technology Corporation
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LD7536
Package Information
DIP-8
Symbol
Dimension in Millimeters
Dimensions in Inches
Min
Max
Min
Max
A
9.017
10.160
0.355
0.400
B
6.096
7.112
0.240
0.280
C
-----
5.334
------
0.210
D
0.356
0.584
0.014
0.023
E
1.143
1.778
0.045
0.070
F
2.337
2.743
0.092
0.108
I
2.921
3.556
0.115
0.140
J
7.366
8.255
0.29
0.325
L
0.381
------
0.015
--------
Important Notice
Leadtrend Technology Corp. reserves the right to make changes or corrections to its products at any time without notice. Customers
should verify the datasheets are current and complete before placing order.
15
Leadtrend Technology Corporation
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LD7536
Revision History
Rev.
Date
Change Notice
00
2/25/2010
Original Specification
00a
3/15/2010
Start-up resistor value (max): 1.8M
OTP source current (min.) 77μA
01
7/1/2010
OLP trip level (min.) (max.)
01
11/8/2010
VCC OVP TC Curve for APD
16
Leadtrend Technology Corporation
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