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PDF LD7890 Data sheet ( Hoja de datos )
| Número de pieza | LD7890 | |
| Descripción | High Voltage 4-Channel LED Controller Driver | |
| Fabricantes | Leadtrend | |
| Logotipo |  |
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LD7890
11/5/2013
High Voltage 4-Channel LED Controller Driver
REV: 01
General Description
The LD7890 is a 4-channel LED controller with a boost
switching controller. It’s an ideal solution for driving high
power LED backlights. The LD7890 can deliver high
accuracy of constant current to 4 individual LED strings
with 4 External MOSFET without cross-reference.
The LD7890 is designed for Current-Mode Boost
Controller, capable to operate over a wide range VIN from
9V to 28V and build in the High voltage MOSFET gate to
reduce external Power MOSFET thermal issue.
The other features include LED short and open protection,
cycle by cycle current limit, and thermal shutdown.
Typical Application
VIN
Cin
10V
NMOS
Features
Input Voltage range: 9V to 28V
4 Channel LED Controller
External and Internal PWM dimming control
LED short circuit protection
LED open string protection
Cycle-by-Cycle Current Limit
Over-temperature protection
Status output
Applications
LED TV Backlight
LED Monitor Backlight
LED Lighting
33uF
R1
OVP
EN
S3
G3
D3
S4
G4
D4
LD7890
VIN DRV
OVP
EN
RT
COMP
PARL
GND
CS
DIM
LOSC
STATUS
Sense1
Gate1
FB1
Sense2
Gate2
FB2
FB4
Gate4
Sense4
FB3
Gate3
Sense3
OVP
R2
PWM
5V
D3
G3
S3
D4
G4
S4
Fig. 1 Application circuit for 4 strings of LED light bar with External PWM
Leadtrend Technology Corporation
LD7890-DS-01 November, 2013
1
www.leadtrend.com.tw
1 page  
Block Diagram
RT
LD7890
DRV
STATUS
GND
OVP
EN
VIN
EN
Oscillator
Current
Limit
0.5V
GDRV
Logic
QS
R
Σ
COMP
LEB
VSET
GM
Protection
Logic
OR
OVP
SCP
LED
2.5V Voltage
LED Short
LED
Detector
SP
4
LED Open
0.2V
4
4
Vref PWM
Vref PWM
LDO
0.2V
Internal
Reference
Reference
PWM
Vref PWM
PWM
Vref
CS
COMP
FB1
Gate1
SENSE1
FB2
Gate2
SENSE2
FB3
Gate3
SENSE3
FB4
Gate4
SENSE4
DIM LOSC
PARL
Leadtrend Technology Corporation
LD7890-DS-01 November, 2013
5
www.leadtrend.com.tw
5 Page 
LD7890
blanking time to suppress the switching noise from the
external MOSFET. A PWM comparator compares the
current-sense voltage and the slop compensation signal
with the output of the GM error amplifier. The device will
turn off the external MOSFET when the voltage across CS
exceeds the error amplifier’s output voltage. This process
repeats every switching cycle to achieve peak
current-mode control.
The LD7890 is integrated with under-voltage lockout
(UVLO) function. The device will be disabled as VIN pin’s
voltage drops below UVLO threshold of 7.5V and will not
resume until it rises up to 8.9V.
Start Up Sequence
As EN is activated, the IC will start to check if OVP’s
voltage is above 0.2V. If confirmed, the DIM pin will signal
high to boost internal soft start. The Soft start function
would limit inductor current to let it rise linearly and
minimize the input inrush current.
Multi-Chip Parallel Operation
If used in some applications requiring more than 4 strings
or LED, just connect desired numbers of LD7890 in
parallel in a single power stage for it.
In multiple chips operation, each PARL pins should be
connected together and set the master chip to control the
driving signal to the external NMOSFET. Leave the
remaining chips work in slave mode according to the
following terms
(1): Float DRV pin
(2): Short CS to AGND
(3): Slave OVP pin Setting lower than Master
(4): LOSC pin parallel.
Loop compensation
The LD7890 has an internal error amplifier for LED
current regulation for COMP output to compensate the
control loop. The selection of the inductor, output
capacitor, compensation resistor and capacitor would
affect the loop stability. The inductor and output capacitor
are determined based on the terms of performance, size
and cost, while the compensation resistor and capacitor
for COMP are according to the criteria to optimize control
loop stability.
Switching Frequency Selection
LD7890 can operate in fixed frequency mode. The
constant operation frequency is set by an external resistor
connected between RT pin and ground. The resistor sets
the charging current for internal oscillator.
FSW
(kHz)
70750
[RT(k)]
28.3
Programming the LED Current
The SENSE pins detect the voltage of the external LED
current bias resistors and individually regulate accurate
voltage to 0.4V. They cooperate with the internal
compensation circuits to eliminate the operating GATE
[1:4] current for NMOS’s use to secure extremely accurate
LED current matching with each the individual and
independent channel.
ILED
(A)
0.4V
RSENSE
()
External PWM dimming
PWM dimming control will be achieved by applying an
external PWM signal between 100Hz and 800Hz to the
DIM pin.
Internal PWM dimming
Apply DC Voltage (0.2~1.2V) to the DIM Pin in compare
with the LOSC signal to enable PWM Dimming. The
internal frequency is determined by the external capacitor.
If the external capacitor is 2.2nF, its internal frequency is
1KHz typically.
The PWM dimming duty is determined by the DC voltage
ranging between 0.2V and 1.2V. Larger DC voltage
usually produces greater brightness.
Leadtrend Technology Corporation
LD7890-DS-01 November, 2013
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LD7890.PDF ] | |
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