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PDF LD7820 Data sheet ( Hoja de datos )

Número de pieza LD7820
Descripción Primary-Side PWM Controller
Fabricantes Leadtrend 
Logotipo Leadtrend Logotipo



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LD7820
04/08/2012
Primary-Side PWM Controller with CV/CC Operation for LED
REV:00
General Description
The LD7820 is a primary-side feedback controller in CV/CC
operation for LED lighting applications. It minimizes the
components counts and is available in tiny packages. Those
make it an ideal design for low cost applications.
The LD7820 provides constant voltage, constant current
(CV/CC) operation requiring neither photo-coupler nor
secondary control circuit. Also, the LD7820 features OTP
(Over Temperature Protection) and OVP (Over Voltage
Protection) to prevent the circuit from being damaged under
abnormal conditions.
Features
Primary-side Feedback Control
Constant Current Control
Built-in Load Regulation Compensation
Built-in Primary Winding Inductance Compensation
Low Startup Current (<16A)
Current Mode Control with Cycle-by-Cycle Current Limit
Green Mode Control
UVLO (Under Voltage Lockout)
LEB (Leading-Edge Blanking) on CS Pin
OVP (Over Voltage Protection) on Vcc
OTP (Over Temperature Protection)
300mA Driving Capability
Applications
AC-DC LED Driver
Typical Application
Leadtrend Technology Corporation
LD7820-DS-00 April 2012
1
www.leadtrend.com.tw

1 page




LD7820 pdf
LD7820
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
Supply Voltage (Vcc Pin)
Startup Current
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V
VCOMP=3.5V,
OVP tripped
UVLO (off)
UVLO (on)
Vcc OVP Level
MIN
TYP
MAX UNITS
10 16 A
1.8 mA
3.0 mA
0.65
mA
7.0 8
9V
15 16 17 V
25 26 27 V
Error Amplifier (CV mode, Comp pin, FB pin)
Reference Voltage, Vref
2.47
2.500
2.53
V
Transconductance
14 mho
Output Sink Current
Output Source Current
Output Upper Clamp Voltage
VFB=3.2V, VCOMP=2.5V
VFB=1.8V, VCOMP =2.5V
VFB=2.3V
75 A
-75 A
4.0 4.1 4.2 V
Load Compensation Current
VCS=0.75V
10.5
13.5 16.5
A
Load Compensation Cut-off Voltage Load compensation current=0A*
0.2
V
Sample and Hold
Sampling Delay Time
Sampling Time
*
*
1.8 s
0.4 s
Current Sensing (CS Pin)
Maximum Input Voltage, Vcs(off)
Vcs-min
Leading Edge Blanking Time
Input impedance
Delay to Output
VCOMP < 1.8V
*
0.83
350
1
0.85
0.2
420
80
0.87
490
V
V
ns
M
ns
Leadtrend Technology Corporation
LD7820-DS-00 April 2012
5
www.leadtrend.com.tw

5 Page





LD7820 arduino
LD7820
VDS
The undershoots
would make the
sample error.
Fig.18
VIN
Np Ns
Rs
LD7820
OUT
CS
COMP
Fig.19
Load Regulation Compensation
In LD7820, load regulation compensation is implemented to
compensate the cable voltage droop and to achieve a better
voltage regulation. An offset voltage is generated at FB by
an internal sink current source flowing into the FB during the
sample period. The built-in sink current source is
proportional to the peak value of Vcs. As a result, it is
proportional to the output load current, thus the drop due to
the cable loss can be compensated. As the load current
decreases from full-load to no-load, the offset voltage at FB
will decrease. It can also be programmed by adjusting the
resistance of the divider to compensate the drop for various
cable lines used. The equation of internal sink current
source is shown as:
IFB (VCS,pk 0.2) * 24.5 (A)
Fig. 20
Principle of C.C. Operation
To support with the proprietary CC/CV control of the
LD7820, a system designed in DCM mode is required for
flyback converter, as shown in Fig. 21. The output current Io
can be expressed as:
Io
1
2
iS,PK TDIS
TS
1
2
NP
NS
iP,PK
TDIS
Ts
1
2
NP
NS
VCSOFF
RS
TDIS
TS
As a result, the output current Io can be controlled by the
Vcs-off and Ts. In the C.C. mode, Vcs-off will be controlled
as a constant, 0.85V and the ratio of Tdis/Ts will be
modulated as a constant (Tdis/Ts=0.4). In order to let
TDIS/TS=0.4, the switching frequency will be programmed
according to TDIS, as shown as flows:
fS
1
TS
0.4
TDIS
The C.C. point and maximum output power can be
externally adjusted through external current sense resistor
Rs of CS pin. Larger Rs will produce smaller CC point and
less output power or otherwise shown in Fig. 22.
Leadtrend Technology Corporation
LD7820-DS-00 April 2012
11
www.leadtrend.com.tw

11 Page







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