LD7552BPS [LEADTREND]
Green-Mode PWM Controller with Integrated Protections;
| 型号： | LD7552BPS |
| 厂家： | 
Leadtrend Technology |
| 描述： | Green-Mode PWM Controller with Integrated Protections |
| 文件： | 总16页 (文件大小：300K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LD7552B
1/2/2008
Green-Mode PWM Controller with Integrated Protections
Rev. 01a
General Description
Features
The LD7552B are low cost, low startup current, current
z
High-Voltage CMOS Process with Excellent ESD
mode PWM controllers with green-mode power- saving
protection
operation.
The integrated functions include the
z
z
z
z
z
z
z
z
z
z
Very Low Startup Current (<20μA)
Current Mode Control
leading-edge blanking of the current sensing, internal slope
compensation. They provide the users a superior AC/DC
power application of higher efficiency, low external
component counts, and lower cost solution.
Non-audible-noise Green Mode Control
UVLO (Under Voltage Lockout)
LEB (Leading-Edge Blanking) on CS Pin
Programmable Switching Frequency
Internal Slope Compensation
OVP (Over Voltage Protection) on Vcc Pin
OLP (Over Load Protection)
500mA Driving Capability
Furthermore, LD7552B feature more protections like OLP
(Over Load Protection) and OVP (Over Voltage Protection)
to eliminate the external protection circuits. It is designed for
the switching adaptor with 30W~60W output, offered in both
SOP-8 and DIP-8 package.
Applications
z
z
z
Switching AC/DC Adaptor and Battery Charger
Open Frame Switching Power Supply
384X Replacement
Typical Application
AC
EMI
input
Filter
VCC
32V
16.0V
UVLO
OUT
/10.0V
LD7552B
OSC
RT
Control
Logic
photocoupler
TL431
COMP
Divider
CS
GND
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Pin Configuration
SOP-8 & DIP-8 (TOP VIEW)
8
7
6
5
YY: Year code (D: 2004, E: 2005…..)
WW: week code
PP: production code
TOP MARK
YYWWPP
1
2
3
4
Ordering Information
Part number
LD7552B PS
LD7552B GS
LD7552B PN
Package
PB Free
Green Package
PB Free
TOP MARK
Shipping
SOP-8
SOP-8
DIP-8
LD7552BPS
LD7552BGS
LD7552BPN
2500 /tape & reel
2500 /tape & reel
3600 /tube /carton
The LD7552B is ROHS Compliant/ Green Package.
Pin Descriptions
PIN
NAME
FUNCTION
1
GND
Ground
Voltage feedback pin (same as the COMP pin in UC384X), By connecting a
photo-coupler to close the control loop and achieve the regulation.
Supply voltage pin
2
3
4
COMP
VCC
RT
This pin is to program the switching frequency. By connecting a resistor to ground
to set the switching frequency.
5
6
7
8
NC
CS
Unconnected pin
Current sense pin, connect to sense the MOSFET current
Supply voltage pin
VCC
OUT
Gate drive output to drive the external MOSFET
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Block Diagram
∑
* Note: OLP delay is 60mS when the switching frequency is set as 65KHz.
The OLP delay time is proportional to the period of switching cycle.
1
That is, TOLP _ delay ∝ Ts =
.
fs
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Absolute Maximum Ratings
Supply Voltage VCC
30V
COMP, RT, CS
-0.3 ~7V
150°C
Junction Temperature
Operating Ambient Temperature
Storage Temperature Range
-40°C to 85°C
-65°C to 150°C
160°C/W
100°C/W
400mW
650mW
260°C
Package Thermal Resistance (SOP-8)
Package Thermal Resistance (DIP-8)
Power Dissipation (SOP-8, at Ambient Temperature = 85°C)
Power Dissipation (DIP-8, at Ambient Temperature = 85°C)
Lead temperature (Soldering, 10sec)
ESD Voltage Protection, Human Body Model
ESD Voltage Protection, Machine Model
Gate Output Current
3KV
300V
500mA
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.
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage (Vcc Pin)
Startup Current
8
20
μA
mA
mA
mA
V
VCOMP=0V
VCOMP=3V
2.0
3.0
Operating Current
2.5
(with 1nF load on OUT pin)
Protection tripped (OLP, OVP)
0.5
UVLO (Off)
9.0
10.0
16.0
28.0
11.0
17.0
29.5
UVLO (On)
15.0
26.5
V
OVP Level
V
Voltage Feedback (Comp Pin)
Short Circuit Current
Open Loop Voltage
Green Mode Threshold VCOMP
Current Sensing (CS Pin)
Maximum Input Voltage, Vcs(off)
Leading Edge Blanking Time
Input impedance
VCOMP=0V
1.5
6.0
2.2
mA
V
COMP pin open
2.35
V
0.80
1
0.85
350
0.90
V
nS
MΩ
nS
Delay to Output
100
Oscillator (RT pin)
Frequency
RT=100KΩ
60
65
20
5
70
KHz
KHz
%
Green Mode Frequency
Temp. Stability
Fs=65KHz
(-40°C ~105°C)
(VCC=11V-25V)
Voltage Stability
1
1
%
Gate Drive Output (OUT Pin)
Output Low Level
VCC=15V, Io=20mA
V
V
Output High Level
VCC=15V, Io=20mA
9
Rising Time
Load Capacitance=1000pF
Load Capacitance=1000pF
50
30
160
60
nS
nS
Falling Time
OLP (Over Load Protection)
OLP Trip Level
VCOMP(OLP)
Fs=65KHz
5.0
60
V
OLP Delay Time (note)
mS
Note: The OLP delay time is proportional to the period of switching cycle. So that, the lower RT value will set the higher switching
frequency and the shorter OLP delay time.
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Typical Performance Characteristics
12
18.0
11.2
17.2
16.4
15.6
14.8
14.0
10.4
9.6
8.8
8
-40
0
40
80
120 125
-40
0
40
80
120 125
Temperature (°C)
Temperature (°C)
Fig. 1 UVLO (on) vs. Temperature
Fig. 2 UVLO (off ) vs. Temperature
26
24
22
20
18
16
70
68
66
64
62
60
-40
0
40
80
120 125
0
120 125
-40
40
80
Temperature (°C)
Temperature (°C)
Fig. 3 Frequency vs. Temperature
Fig. 4 Green Mode Frequency vs. Temperature
25
23
21
70
68
66
64
19
17
62
60
15
11 12
14
16
18
20
22
24 25
11
12
14
16
18
20
22
24 25
Vcc (V)
Vcc (V)
Fig. 5 Frequency vs. Vcc
Fig. 6 Green Mode Frequency vs. Vcc
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
85
80
75
70
0.90
0.88
0.86
0.84
0.82
0.80
65
60
-40
0
40
80
120 125
-40
0
40
80
120 125
120 125
120 125
Temperature (°C)
Temperature (°C)
Fig. 7 Max Duty vs. Temperature
Fig. 8 VCS (off) vs. Temperature
12
35
30
25
20
15
10
10
8
6
4
2
0
-40
0
40
80
120 125
-40
0
40
80
Temperature (°C)
Temperature (°C)
Fig. 10 VCC OVP vs. Temperature
Fig. 9 Startup Current (Istartup) vs. Temperature
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
6.0
5.5
5.0
4.5
-40
0
40
80
120 125
-40
0
40
80
Temperature (°C)
Temperature (°C)
Fig. 12 OLP-Trip Level vs. Temperature
Fig. 11 VCOMP open loop voltage vs. Temperature
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Application Information
will help to increase the value of R1 and then reduce the
power consumption on R1. By using CMOS process and the
special circuit design, the maximum startup current of
LD7552B is only 20μA.
Operation Overview
The LD7552B meet the green-power requirement and are
intended for the use in those modern switching power
suppliers and adaptors that demand higher power efficiency
and power-saving. They integrated more functions to reduce
the external component counts and the size. Their major
features are described as below.
If a higher resistance value of the R1 is chosen, it usually
takes 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 voltage
enough to turn on the LD7552B 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)
Fig. 14
t
I(Vcc)
operating current
(~ mA)
Current Sensing and Leading-edge Blanking
The typical current mode of PWM controller feedbacks both
current signal and voltage signal to close the control loop
and achieve regulation. As shown in Fig. 15, the LD7552B
detect the primary MOSFET current from the CS pin, which
is not only for the peak current mode control but also for the
pulse-by-pulse current limit. The maximum voltage
threshold of the current sensing pin is set at 0.85V. From
above, the MOSFET peak current can be obtained from
below.
startup current
(~uA)
t
Fig. 13
Startup Current and Startup Circuit
The typical startup circuit to generate the LD7552B Vcc is
shown in Fig. 14. During the startup transient, the Vcc is
lower than the UVLO threshold thus there is no gate pulse
produced from LD7552B to drive power MOSFET.
Therefore, the current through R1 will provide the startup
current and to charge the capacitor C1. Whenever the Vcc
voltage is high enough to turn on the LD7552B and further
to deliver the gate drive signal, the supply current is
provided from the auxiliary winding of the transformer.
Lower startup current requirement on the PWM controller
0.85V
I
=
PEAK(MAX)
R
S
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Vin
R1
Cbulk
D1
C1
VCC
OUT
LD7552B
Comp
CS
GND
Rs
Fig. 15
A 350nS 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 350nS and the negative spike
on the CS pin doesn’t exceed -0.3V, it could eliminated the
R-C filter (as shown in the figure16).
Fig. 16
However, the total pulse width of the turn-on spike is
decided by the output power, circuit design and PCB layout.
It is strongly recommended to adopt a smaller R-C filter (as
shown in figure 17) for higher 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 500mA
driving capability, is incorporated to drive a power MOSFET
directly. And the maximum duty-cycle of LD7552B is
limited to 75% to avoid the transformer saturation.
Oscillator and Switching Frequency
Connect a resistor from RT pin to GND according to the
equation below to program the normal switching frequency:
Fig. 17
65.0
f
=
×100(KHz)
SW
RT
(KΩ)
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 LD7552B. Similar to UC384X, the LD7552B
would carry 2 diodes voltage offset at the stage to feed the
voltage divider at the ratio of 1/3, that is,
The operating frequency range for the LD7552B is
recommended to set between 50KHz and 130KHz.
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
On the other hand, if the OVP condition is removed, the Vcc
level will get back to normal level and the output will
automatically return to the normal operation.
1
V−(PWM
= ×(VCOMP − 2VF )
)
COMPARATOR
3
A pull-high resistor is embedded internally and can be
eliminated externally.
The OVP levels are 28.0V ± 1.5V.
Internal Slope Compensation
In the conventional application, the problem of the stability is
a critical issue for current mode controlling, when it operates
in higher than 50% of the duty-cycle. As UC384X, It takes
slope compensation from injecting the ramp signal of the
RT/CT pin through a coupling capacitor. It therefore requires
no extra design for the LD7552B since it has integrated it
already.
On/Off Control
The LD7552B can be turned off by pulling COMP pin lower
than 1.2V. The gate output pin of the LD7552B will be
disabled immediately under such condition. The off-mode
can be released when the pull-low signal is removed.
Fig. 18
Over Load Protection (OLP)
To protect the circuit from being damaged under over load
condition or short condition, a smart OLP function is
implemented in the LD7552B. The figure 19 shows the
waveforms of the OLP operation. In this case, the feedback
system will force the voltage loop proceed toward the
saturation and then pull up the voltage on COMP pin
(VCOMP). Whenever the VCOMP trips up to the OLP threshold
5V and stays longer than 60mS, the protection will activate
and then turn off the gate output to stop the switching of
power circuit. The 60mS delay time is to prevent the false
trigger from the power-on and turn-off transient.
Dual-Oscillator Green-Mode Operation
There are many different topologies has been implemented
in different chips for the green-mode or power saving
requirements such as “burst-mode control”, “skipping-cycle
mode”, “variable off-time control “…etc. The basic operation
theory of all these approaches intended to reduce the
switching cycles under light-load or no-load condition either
by skipping some switching pulses or reduces the switching
frequency.
OVP (Over Voltage Protection) on Vcc
The VGS ratings of the nowadays power MOSFETs are often
limited up to max. 30V. To prevent the VGS from the fault
condition, LD7552B are implemented an OVP function on
Vcc. Whenever the Vcc voltage is higher than the OVP
threshold voltage, the output gate drive circuit will be
shutdown simultaneously thus to stop the switching of the
power MOSFET until the next UVLO(on).
By such protection mechanism, the average input power
can be reduced to very low level so that the component
temperature and stress can be controlled within the safe
operating area.
The Vcc OVP function in LD7552B is an auto-recovery type
protection. If the OVP condition, usually caused by the
feedback loop opened, is not released, the Vcc will tripped
the OVP level again and re-shutdown the output. The Vcc
is working as a hiccup mode. The figure 18 shows its
operation.
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
VCC
UVLO(on)
UVLO(off)
OLP
60mS
UVLO(off)
OLP Reset
t
t
t
COMP
5.0V
OLP trip Level
OUT
Switching
Non-Switching
Switching
Fig. 19
Fault Protection
There are several critical protections were integrated in the
LD7552B to prevent the power supply or adapter from being
damaged. Those damages usually come from open or short
condition on the pins of LD7552B. Under the conditions
listed below, the gate output will turn off immediately to
protect the power circuit ---
y
y
y
RT pin short to ground
RT pin floating
CS pin floating
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Reference Application Circuit #1 --- 40W (5V/2A & 12V/2.5A) Adapter with
2-Stage Startup Circuit
Pin < 0.3W when Pout = 0W
F1
FL1
FL2
R51B
C51
R51A
R1A
R1B
L51
5V
CX1
AC
input
CY2
CY3
T1
BD1
R2A
R2C
R2E
R3A
R3B
C53
C52
C2
R99
R4A
CR51
C1
GND
12V
NTC1
R5A
R4B
D1
R121B
R121A
D3
D2
R5B
C121
ZD121
L121
R6
L2
C10
C4
C8
C122
C123
R100
IC1
CR121
D4
GND
Q1
VCC
OUT
LD7552B
R10
CS
GND COMP
R14
R9
RT
RT
C5
R8
R54
photocoupler
C6
IC2
R52
R53
C55
R55
CY1
R121
R122
IC51
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
BOM
P/N
C1
Component Value
Note
P/N
R1A
R1B
R2A
R2C
R3A
R3B
R4A
R4B
R5A
R5B
R6
Component Value
1MΩ, 1206
Original
100μF, 400V
L-tec
C2
1000pF, 1000V, 1206 X7R
1MΩ, 1206
C4
10μF, 50V
L-tec (LZG)
510KΩ, 1206
510KΩ, 1206
1MΩ, 1206
C5
100pF, 50V, 0805
0.022μF, 50V, 0805
33μF, 50V
X7R
C6
X7R
Open
Open
C8
L-tec (LZG)
X7R
1MΩ, 1206
C10
C51
C52
C53
C55
C121
C122
C123
CX1
CY1
CY2
CY3
D1
0.1μF, 50V, 0805
1000pF, 250V, 1206
470μF, 16V
100KΩ, 1206
100KΩ, 1206
100Ω, 1206
100Ω, 1206
10Ω, 1206
L-tec (LZG)
L-tec (LZG)
X7R
1000μF, 25V
0.01μF, 50V, 0805
1000pF, 250V, 1206
1000μF, 25V
R8
0.47Ω, 1W
L-tec (LZG)
L-tec (LZG)
R9
1.5KΩ, 0805
10Ω, 1206
470μF, 16V
R10
R14
RT
0.22μF,X-cap
2200pF,Y-cap, class2
2200pF,Y-cap, class2
2200pF,Y-cap, class2
1N4007
0Ω, 0805
100KΩ, 0805,1%
100Ω, 1206
100Ω, 1206
R51A
R51B
R121A 100Ω, 1206
R121B 100Ω, 1206
D2
PS102R
D3
1N4148
R52
3.6KΩ, 0805, 1%
D4
1N4148
R53
2.49KΩ, 0805, 1%
200Ω, 0805
1KΩ, 0805
N/A
ZD51
5V1B
R54
ZD121 7.5V, 1W
ZD122 15V
R55
R99A
R99B
Q1
6A, 600V
2A, 600V
10A, 100V
SSS6N60A
2KBP06M
Y1010DN
N/A
BD1
CR51
R100A N/A
R100B N/A
CR121 10A, 60V
SBL1060CF
Leadtrend
EVERLIGHT
R121
R122
FL1
FL2
T1
33KΩ, 0805
IC1
IC2
IC51
F1
LD7552B
EL817B
1KΩ, 0805
Leadtrend’s Design
Leadtrend’s Design
Leadtrend’s Design
Bead Core
TL431, 1%
250V,T2A
Walter
L2
L51
L121
Leadtrend’s Design
Leadtrend’s Design
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Package Information
SOP-8
Dimension in Millimeters
Dimensions in Inches
Symbol
Min
4.801
3.810
1.346
0.330
1.194
0.178
0.102
5.791
0.406
0°
Max
5.004
3.988
1.753
0.508
1.346
0.229
0.254
6.198
1.270
8°
Min
5.004
3.988
1.753
0.508
1.346
0.229
0.254
6.198
1.270
0°
Max
0.197
0.157
0.069
0.020
0.053
0.009
0.010
0.244
0.050
8°
A
B
C
D
F
H
I
J
M
θ
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Package Information
DIP-8
Dimension in Millimeters
Dimensions in Inches
Symbol
Min
Max
10.160
7.112
5.334
0.584
1.778
2.743
3.556
8.255
---
Min
0.355
0.240
---
Max
0.400
0.280
0.210
0.023
0.070
0.108
0.140
0.325
---
A
B
C
D
E
F
I
9.017
6.096
-----
0.356
1.143
2.337
2.921
7.366
0.381
0.014
0.045
0.092
0.115
0.290
0.015
J
L
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.
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
LD7552B
Revision History
Rev. Date
Change Notice
00
09/20/2006 Original Specification.
01/29/2007 Revision: Block Diagram
01
01a
1/2/2008
Revision: Green Package Option
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Leadtrend Technology Corporation
LD7552B-DS-01a January 2008
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