ETC LD7537R

LD7537R
7/01/2010
Green-Mode PWM Controller with Frequency Swapping
and Integrated Protections
Rev. 00a
General Description
Features
The LD7537R 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
Brownout Protection
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
AC
input
DC
Output
EMI
Filter
VCC
OUT
BNO
LD7537R
CS
COMP
GND
1
Leadtrend Technology Corporation
LD7537R-DS-00a
July 2010
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photocoupler
LD7537R
Pin Configuration
SOT-26 (TOP VIEW)
COMP
NC
8
7
6
OTP
GND
DIP-8 (TOP VIEW)
OUT
VCC
5
6
5
37R
YWP pp
1
2
TOP MARK
1
2
3
4
OUT
VCC
NC
CS
YYWWPP
GND
YY, Y
WW, W
PP
P37R
Ordering Information
Part number
CS
:
:
:
:
4
3
COMP OTP
Year code (D: 2004, E: 2005…..)
Week code
Production code
LD7537R
Package
Top Mark
Shipping
LD7537R GL
SOT-26
Green Package
YWP/37R
3000 /tape & reel
LD7537R GN
DIP-8
Green Package
LD7537R GN
3600 /tube /Carton
Protection Mode
Switching Freq.
VCC OVP
OLP
BNO Pin
65kHz
Auto recovery
Auto recovery/ 65ms
Auto recovery
Pin Descriptions
SOT-26
DIP-8
NAME
1
8
GND
2
7
COMP
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.
Brownout Protection Pin. Connect a resistor divider between this pin
3
5
BNO
and bulk capacitor voltage to set the brownout level. If the voltage is
less than threshold voltage, the PWM output will be disabled.
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
LD7537R-DS-00a
July 2010
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LD7537R
Block Diagram
∑
3
Leadtrend Technology Corporation
LD7537R-DS-00a
July 2010
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LD7537R
Absolute Maximum Ratings
Supply Voltage VCC
-0.3V ~29V
COMP, BNO, 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)
250mW
Power Dissipation (DIP-8)
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
10
24
V
540K
1.8M
Ω
4
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LD7537R-DS-00a
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LD7537R
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
VCOMP=0V
1.0
mA
Operating Current
VCOMP=3V
2.0
mA
(with 1nF load on OUT pin)
OLP Tripped/ Auto
0.47
mA
OVP Tripped/ Auto
0.47
mA
UVLO (off)
7.5
8.5
9.5
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
2.4
V
Zero Duty Threshold VCOMP
1.5
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
65
70
kHz
22
kHz
± 4.0
kHz
5
%
Temp. Stability
(-20°C ~85°C)
Voltage Stability
(VCC=11V-25V)
1
%
Output Low Level
VCC=15V, Io=20mA
1
V
Output High Level
VCC=15V, Io=20mA
8
Rising Time
Load Capacitance=1000pF
--
Falling Time
Output High Clamp Level
Gate Drive Output (OUT Pin)
170
350
ns
Load Capacitance=1000pF
50
100
ns
VCC=20V
16
V
75
%
Max. Duty
5
Leadtrend Technology Corporation
LD7537R-DS-00a
July 2010
V
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LD7537R
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
4.3
4.5
4.7
V
OLP (Over Load Protection)
OLP Trip Level
65
OLP Delay Time
ms
Brownout Protection (BNO Pin)
Brownout Turn-On Trip Level
1.00
1.05
1.10
V
Brownout Turn-Off Trip Level
0.75
0.80
0.85
V
BNO Pin De-bounce Time
250
us
OTP Level
140
°C
OTP Hysteresis
30
°C
2
ms
On Chip OTP (Over Temperature)
Soft Start Duration
Soft Start Duration
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LD7537R-DS-00a
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LD7537R
18.0
10.6
17.2
9.8
UVLO (off) (V)
UVLO (on) (V)
Typical Performance Characteristics
16.4
15.6
6.6
-40
0
40
Fig. 1
80
120 125
-40
120
125
Fig. 2 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
Temperature (°C)
68
66
64
62
60
11
40
0
Temperature (°C)
UVLO (on) vs. Temperature
70
Frequency (KHz)
8.2
7.4
14.8
14.0
9.0
12
14
16
18
20
22
24
July 2010
17
12
14
16
18
20
22
Fig. 6 Green Mode Frequency vs. Vcc
7
LD7537R-DS-00a
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 (%)
LD7537R
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
LD7537R-DS-00a July 2010
40
80
Temperature (°C)
Fig. 12 OLP-Trip Level vs. Temperature
Fig. 11 VCOMP open loop voltage vs. Temperature
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120 125
LD7537R
Application Information
Operation Overview
current. Lower startup current requirement on the PWM
The LD7537R 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 LD7537R 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
voltage on the VCC pin. It would assure the supply
AC
input
voltage enough to turn on the LD7537R PWM controller
EMI
Filter
and further to drive the power MOSFET. As shown in Fig.
Cbulk
D1
13, a hysteresis is built in to prevent the shutdown from
R1
the voltage dip during startup. The turn-on and turn-off
C1
threshold level are set at 16.0V and 8.5V, respectively.
VCC
Vcc
OUT
UVLO(on)
LD7537R
UVLO(off)
CS
GND
t
Fig. 14
I(Vcc)
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
LD7537R detects the primary MOSFET current from the
The typical startup circuit to generate VCC of the LD7537R
CS pin, which is not only for the peak current mode
is shown in Fig. 14. During the startup transient, the VCC
control but also for the pulse-by-pulse current limit. The
is below UVLO threshold. Before it has sufficient voltage
maximum voltage threshold of the current sensing pin is
to develop OUT pulse to drive the power MOSFET, R1 will
set at 0.85V. From above, the MOSFET peak current can
provide the startup current to charge the capacitor C1.
be obtained from below.
Once VCC obtains enough voltage to turn on the LD7537R
IPEAK (MAX ) =
and further to deliver the gate drive signal, it will enable
the auxiliary winding of the transformer to provide supply
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0.85 V
RS
LD7537R
V−(PWM COMPARATOR ) =
RB
× ( VCOMP − VF )
RA + RB
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 applications, 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.
It is strongly recommended to adopt a
Fig. 16
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
LD7537R 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 LD7537R.
Similar to UC3842, the
LD7537R would carry a diode voltage offset at the stage
to feed the voltage divider at the ratio of RA and RB, that
Fig. 17
is,
10
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LD7537R
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 LD7537R since it has
integrated it already.
4.5V
OLP trip Level
t
On/Off Control
OUT
The LD7537R can be turned off by pulling COMP pin
lower than 1.5V. The gate output pin of the LD7537R will
Switching
be disabled immediately under such condition. The
Non-Switching
Switching
off-mode can be released when the pull-low signal is
t
removed.
Fig. 18
OVP (Over Voltage Protection) on Vcc Over
Load
Protection
(OLP)
-
Auto
Auto Recovery
Recovery
The maximum VGS ratings of the power MOSFETs are
To protect the circuit from damage due to over-load
mostly for 30V. To prevent the VGS enter fault condition,
condition and short or open-loop condition, the LD7537R
LD7537R series are implemented with OVP function on
is implemented with smart OLP function. It also features
Vcc. Whenever the Vcc voltage is higher than the OVP
auto recovery function; see Fig. 18 for the waveform. In
threshold, the output gate drive circuit will be shutdown
case of fault condition, the feedback system will force the
simultaneously and the switching of the power MOSFET
voltage loop toward the saturation and then pull the
is disabled until the next UVLO(on).
voltage high on COMP pin (VCOMP). When the VCOMP
The Vcc OVP functions of LD7537R are auto-recoverable.
ramps up to the OLP threshold of 4.5V and continues over
If the OVP condition, usually caused by open-loop of
OLP delay time, the protection will be activated and then
feedback, is not released, the Vcc will tripped the OVP
turn off the gate output to stop the switching of power
level again and re-shutdown the output. The Vcc works
circuit.
in hiccup mode. Figure 19 shows its operation.
With the protection mechanism, the average input power
Otherwise, when the OVP condition is removed, the Vcc
will be minimized to remain the component temperature
level will be resumed and the output will automatically
and stress within the safe operating area.
return to the normal operation.
11
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LD7537R
VCC
OVP Tripped
OVP Level
UVLO(on)
UVLO(off)
t
OUT
Switching
Non-Switching
Switching
t
Fig. 19
Brownout Protection
The LD7537R programmable to set the brownout
protection point though BNO pin. The voltage across the
BNO pin is proportional to the bulk capacitor voltage,
referred as the line voltage.
A brownout comparator is
implemented to detect the abnormal line condition. As
soon as the condition is detected, it will shut down the
Fig. 20
controller to prevent the damage. Figure 20 shows the
operation.
When VBNO falls below 0.80V, the gate
Oscillator and Switching Frequency
output will be kept off even Vcc has already achieved
UVLO(ON). It therefore makes Vcc hiccup between
The LD537R is implemented with Frequency Swapping
UVLO(ON) and UVLO(OFF).
Unless the line voltage is
function which helps the power supply designers to both
large enough to pull VBNO larger than 1.05V, the gate
optimize EMI performance and lower system cost. The
output will not start switching even when the next
switching frequency substantially centers at 65KHz, and
UVLO(ON) is tripped. A hysteresis is implemented to
swap between a range of ±4KHz.
prevent the false trigger during turn-on and turn-off. Figure
Green-Mode Operation
20 shows the circuit.
By using the green-mode control, the switching frequency
can be reduced under the light load condition. This feature
helps to improve the efficiency in light load conditions.
The green-mode control is Leadtrend Technology’s own
property.
Fault Protection
There are several critical protections integrated in the
LD7537R to prevent from damage to the power supply.
12
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LD7537R
Those damages usually come from open or short
conditions on the pins of LD7537R.
In case under such conditions listed below, the gate
output will turn off immediately to protect the power circuit.
1.
CS pin floating
2.
COMP pin floating
13
Leadtrend Technology Corporation
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LD7537R
Reference Application Circuit --- 40W (19V/2.1A) Adapter
3.15A/250V
L
N
BD1
2 COMP
3
BNO
NC
BD1
5 VCC
CS 4
OUT 6
LD7537R
1
GND
D6
RM8
IC432
SMD
ZENER1
LD7537R-DS-00a July 2010
www.leadtrend.com.tw
+Vo
RTN
14
Leadtrend Technology Corporation
LD7537R
Package Information
SOT-26
Symbol
Dimension in Millimeters
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°
15
Leadtrend Technology Corporation
LD7537R-DS-00a July 2010
Dimensions in Inches
www.leadtrend.com.tw
LD7537R
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.
16
Leadtrend Technology Corporation
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LD7537R
Revision History
Rev.
Date
Change Notice
00
5/11/2010
Original Specification
00a
7/1/2010
Output High Clamp Level Spec.
17
Leadtrend Technology Corporation
LD7537R-DS-00a July 2010
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