Fig. 1 VIN=24V, “DIM Turn On, Duty=100%”
Fig. 2 VCC=24V, “Steady State, Duty=100%”
Fig. 3 VIN=24V, “fDIM=20kHz ,Dim Duty=90%”
Fig. 4 VIN=24V, “ fDIM=20kHz, Duty=50%
SCP 0.2V
2.0V
Slope Compensation
CS
LEB
GND
Vref OK
2.5V FB
OVP SCP
LED SHORT
Osillator
PWM Comparator
SQ R
0.45
OCP Comparator
Voltage Divider
&
GM
Buffer
Driver Stage
12V
VOVP
1.86
2
2.14
V
VOSP
0.17
V
150
°C
30
°C
Leadtrend Technology Corporation LD5857-DS-00 April 2014
6

Typical Performance Characteristics
LD5857
Features
Wide Input Range: 9V to 28V Current Mode Control 0.3V LED Feedback Current Sensing Reference Fixed Switching Frequency Cycle-by-Cycle Current Limit Over Temperature Protection High performance of Dimming Linearity. Programmable PWM Dimming Input and Analog
Dimming Output with Software Control
Applications
LED TV Backlight LED Monitor Backlight LED lighting
Typical Application
VIN
VOUT RA
RB RCS VCC
124
VCC DRV CS
PARAMETER
CONDITIONS
Symbol
Input Power (VCC)
Turn On Levern Off Level
UVLO(off)
UVLO_OFF
Shutdown Current
DIM=Low, over 30ms
IOFFVIN
Operating Current
Part number
Package
TOP MARK
LD5857 GS
SOP-8
LD5857 GS
Note: The LD5857 is ROHS compliant/ Green Packaged.
Shipping 2500 /tape & reel
Pin Descriptions
PIN
NAME
1
VSOCPC-8 (TOP VIEW)
DI M OVP COMP FB
8765
TOP MARK YYWWPP
1 YY2WW3 PP4
YY: Year code WW: Week code PP: Production code
LD5857
VCC DRV GND
CS
Ordering Information
30V -0.3V ~ 5.5V 250mW 160°C/W 150C -40C~ 125C -40C ~ 85C -55C~ 125C 260C 2.0KV 200V
Recommended Operating Conditions Input Supply Voltage DIM Frequency Dimming duty cycle DIM PIN voltage
10.8V ~ 26.4V 200Hz ~ 30KHz 5% ~ 100% 0V ~ 5V
Caution: Stress exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stress above Recommended Operating Conditions may affect device reliability.
0.5
V
nS
Leadtrend Technology Corporation LD5857-DS-00 April 2014
5

PARAMETER
CONDITIONS
Over Voltage Protection
Over Voltage Threshold
OVP
Leadtrend Technology Corporation LD5857-DS-00 April 2014
4

LD5857
Electrical Characteristics
(VCC=12V, TA=25C, unless otherwise noted.)
R_DIM
PWM dimming Frequency
Dimming Duty-Cycle
Shutdown Recover Delay Time (TDOWN)
TRSD
Current Sensing (CS)
Current Sense Input Threshold Voltage
VCS
LEB time
VCOMP
Feedback (FB)
Reference Voltage
VFB
Tolerance of Reference Voltage
PWM Dimming (DIM)
DIM Voltage threshold
Enable Disable
VDIM_H VDIM_L
Resistance from DIM pin to GND
Leadtrend Technology Corporation LD5857-DS-00 April 2014
2

LD5857
Block Diagram
VCC
DIM
DIM
UVLO
VCC OK
Internal Bias & Vref
Vref
8.7V/7.0V
OVP
Analog dimming control
COMP
DRV FB
Leadtrend Technology Corporation LD5857-DS-00 April 2014
3

LD5857
Absolute Maximum Ratings
VCC, DRV, CS, FB, OVP All Other Pins Power Dissipation, PD@85C, SOP-8 Package Thermal Resistance, SOP-8, JA Maximum Junction Temperature Operating Junction Temperature Operating Ambient Temperature Storage Temperature Range Lead Temperature (Soldering, 10sec) ESD Level (Human Body Model) ESD Level (Machine Model)
8 DIM LD5857 FB 5
OVP COMP GND
RFB
763
COVP
Application circuit
Leadtrend Technology Corporation LD5857-DS-00 April 2014
1

Pin Configuration
Boost Controller for LED Backlight
LD5857
4/15/2014
REV: 00
General Description
The LD5857 is a wide-input asynchronous current mode boost controller, capable to operate in the range between 9V and 28V and to generate 12V of voltage to the GATE pin of MOSFET to reduce thermal loss. The current mode control architecture enhances transient response and simplifies the loop compensation. The DIM input enables the brightness control for LED Backlight or LED lighting.
T_LEB
MIN. 7
180 85
0.291 -3.0 2.5 200
5
0.4
TYP.
40 5
200 90 1.2 1.3 12 75 75 3.8 0.3
150
21
0.45 275
MAX. UNITS