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PDF LD7860 Data sheet ( Hoja de datos )
| Número de pieza | LD7860 | |
| Descripción | 1A High-Brightness LED Driver | |
| Fabricantes | Leadtrend | |
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LD7860
12/30/2009
1A High-Brightness LED Driver with Integrated NMOS Switch
REV：00
General Description
The LD7860 is a controller for step-down converters,
operating in continuous conduction mode and ideally for
driving high brightness of power LEDs. The device
operates with inputs from 6V to 30V and utilizes an
external high-side current sense resistor to set the normal
average output current of up to 1A. Depending on the
selection of input voltage and external components, it can
drive up to 7pcs of WLEDs (VF=3.5V). Output current can
be adjusted below the set value, by applying an external
analog or PWM control signal to DIM pin. The device can
operate with the switching frequency of up to 1MHz,
making it ideal for the applications requiring small footprint
and low value external inductors. Some additional
features include under-voltage lockout, over current
protection and thermal shutdown.
Features
z Wide input voltage range: 6V to 30V
z Integrated with 30V NMOS switch
z Up to 1A output current
z Hysteretic Control
z Output current accuracy for ±5% (typ.)
z Up to 1MHz switching frequency
z Brightness control using analog or PWM signal
z High efficiency
z Over current protection
z Over temperature protection
z Inherent open-circuit LED protection
z Output shutdown
Applications
z MR16 or LED bulbs
z Architectural, Ambient and Low-voltage industrial
lightings
z LED replacement for Low-voltage halogen
z General lighting applications
z Indicators or emergency lighting
z LED back-up lighting
Leadtrend Technology Corporation
LD7860-DS-00 December 2009
1
www.leadtrend.com.tw
1 page  
LD7860
Absolute Maximum Ratings
VCC and CS Pin to GND
LX Pin to GND
LX Current
DIM Pin to GND
Power dissipation TSOT-25@Ta=25°C
Package Thermal Resistance TSOT-25
Power dissipation SOT89-5@Ta=25°C
Package Thermal Resistance SOT89-5
Power dissipation MSOP-8@Ta=25°C
Package Thermal Resistance MSOP-8
Operating Ambient Temperature Range
Storage Temperature Range
Maximum Operating Junction Temperature
Lead Temperature (Soldering, 10sec)
ESD Level (Human Body Model)
ESD Level (Machine Model)
-0.3V~32V (33V for 0.5s)
-0.3V~33V (34V for 0.5s)
3.5A
-0.3V~6V
454mW
220°C/W
571mW
175°C/W
625mW
160°C/W
-30°C to 85°C
-55°C to 125°C
125°C
260 °C
2kV
200V
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
Leadtrend Technology Corporation
LD7860-DS-00 December 2009
5
www.leadtrend.com.tw
5 Page 
LD7860
or over 1.5 times of the programmed average LED current.
It’s recommended to select inductors in the range from
12μH to 150μH. Larger inductor possesses less current
ripple and minimizes the error due to propagations delays
due to higher input voltage, lower VLED and light load
situation. Those inductors with lower equivalent series
resistance can improve the efficiency further.
When selecting the inductor, make sure it is capable
to handle the peak current without saturation even at
maximum operating temperature.
Fig.16
Fig. 16 illustrates the actual operating frequency of
LD7860. Following it is an approximate formula.
fSW
=
TON
1
+ TOFF
(Hz)
Where:
TON= TON1 + TDH + TDLR ÆNMOS switch ‘on time’(s).
TOFF= TOFF1 + TDL + TDHR ÆNMOS switch ‘off time’(s).
TON is NMOS switch on time (Neglect TDH and TDLR).
TON1
=
L ⋅ ΔI
VL1
TOFF1 is NMOS switch off time (Neglect TDL and TDHR).
TOFF1
=
L ⋅ ΔI
VL2
VL1 is the across voltage of inductor when NMOS is
switched on.
VL1 = VCC - VSENSE - N ⋅ VLED - ILEDave (rL + RDS(ON) )
VL2 is the across voltage of inductor when NMOS is
switched off.
VL2
= N ⋅ VLED
+V
FD
+ VSENSE
+I
LEDave
⋅ rL
TDHR is the recovery time caused by TDH.
TDHR
=
VL1
VL2
⋅ TDH
TDLR is the recovery time caused by TDL.
TDLR
=
VL2
VL1
⋅ TDL
VCC is the supply voltage (V).
L is the inductance of inductor (H).
ΔI is the inductor peak to peak current ripple of hysteresis
(A).
{Internally set for 30% of ILED(AVE)}
VLED is the total forward conduction voltage of LED (V).
N is the number of LEDs.
ILED(AVE) is the average LED current (A).
rL is the equivalent series resistance of inductor (Ω).
RDS(ON) is the internal switch resistance (Ω).
VFD is the forward conduction voltage of schottky diode
(V).
TDH is comparator for propagation delay time from H to L
(ns).
TDL is comparator for propagation delay time from L to H
(ns).
Leadtrend Technology Corporation
LD7860-DS-00 December 2009
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet LD7860.PDF ] | |
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