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BD9421F Schematic ( PDF Datasheet ) - ROHM Semiconductor

Teilenummer BD9421F
Beschreibung LED Drivers
Hersteller ROHM Semiconductor
Logo ROHM Semiconductor Logo 




Gesamt 30 Seiten
BD9421F Datasheet, Funktion
Datasheet
LED Drivers for LCD Backlights
White LED Driver for large LCD Panels
(DCDC Converter Type)
BD9421F
General Description
BD9421F is high efficiency driver for white LED. This is
designed for large sized LCD. BD9421F is built-in
DCDC converters that supply appropriate voltage for
light source.
BD9421F is also built-in protection function for
abnormal state such as OVP: over voltage protection,
OCP: over current limit protection of DCDC, SCP: short
circuit protection, open detection of LED string.
Thus this is used for conditions of large output voltage
and load conditions.
Features
6ch LED constant current driver(External PNP Tr
Type)
Maximum LED setting current 500mA(VREF Pin
setting)
±2% LED current accuracy(VREF=0.9V setting)
Built-in DC/DC converter
Analog Dimming(Linear) function
LED protection function(OPEN/SHORT
protection)[PWM-independent Type]
Individual detection and individual LED OFF for both
OPEN and SHORT circuit
VOUT Over Voltage Protection(OVP) and reduced
voltage protection(SCP) circuit
Built-in under voltage lockout function(UVLO) and
over voltage protection(OVP)
Built-in VOUT discharge circuit while shutdown
Key Specifications
VCC Supply Voltage Range:
9.0V to 35.0V
DCDC Oscillation Frequency: 150kHz(RT=100k)
Operation Circuit Current:
5mA(Typ)
Operating Temperature Range: -40°C to +85°C
Applications
LED driver for TV, Monitor and LCD Back Light
Package
SOP24
W(Typ) x D(Typ) x H(Max)
15.00mm x 7.80mm x 2.01mm
Pin Pitch 1.27mm
Figure 1. SOP24
Typical Application Circuit
Figure 2. Typical Application Circuit
Product structure : Silicon monolithic integrated circuit
.www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 14 • 001
This product has no designed protection against radioactive rays
1/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com






BD9421F Datasheet, Funktion
BD9421F
Block Diagram
Datasheet
VIN CIN
OVP
Vo
+
VCC
STB
REG75
REF4V
VREG
UVLO
(VCC)
OPEN
SHORT
Detect
Protection
CP counter
OSC CLK
RT
OSC
Control Logic
REG75
PGND
ERROR
OSC CLK
AGND
Soft Start
SS counter
RFB
CFB
FB
-
-
ERR
AMP -
-
VREF*2/3
+
REF4V
0.9V
SHORT_DET
+
+
Comp
+
+
-
1/10
1/10
0.9V
OPEN_DET
-
-
Comp
-
-
+
0.1V
OVP
TSD
OCP
N
CS
PGND
REG75
1/3 VREF
Analog
Dimming
・・・
PWM
Figure 5. Blockdiagram
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
6/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com

6 Page









BD9421F pdf, datenblatt
BD9421F
Datasheet
Maximum DCDC output Voltage
In this IC, the voltage of BSx pin is depending on VREF pin voltage. The maximum voltage of VREF pinVREF3.0V,
the voltage of BSx pin will become 2.0V2/3 of VREF voltage .
The maximum voltage of DCDC output will have been varying with 1.6V while Analog dimming is performed (2/3 of 3.0V -
0.6V).
Soft Start Time setting
This IC have a built in soft start time setting, there is no need to change from the outside. Timer time can be set by
counting the clock frequency with RT pin. Starts counting when shutdown function terminal STB etc is released, and start
time are considered in the count (in soft-start). Therefore, LED OPEN protection SHORT protection are not detected
during this time.
The soft start time is set inside the IC, as the following equation.
(Please note that soft-start time set here is the mask of the running time and not the time until the output stabilizes of the
DCDC. Time to stabilize the output or load is greater than the boost DCDC dependent.)
Soft-start time "TSS", RT pin connection resistor "RRT" :
TSS
[sec]
12480
RRT []
1.5 1010
Start-up sequence
The following describes the start-up sequence of this IC.
STB
OSC
Internal SS
FB SLOPE
PWM
N②
VOUT
ILED
LED_OK
Description of start-up sequence
Set STB from Low to High
System will be activated while PWM=H. SS counting start.
At this time, a circuit in which internal SS voltage for slow start becomes equal to FB pin voltage operates to
equalize the FB pin and internal SS voltages regardless of whether the PWM pin is set to Low or High level.
Since the FB pin and internal SS reach the lower limit of the internal sawtooth wave of the IC, the DC/DC converter
operates to start VOUT voltage rising.
The Vout voltage continues rising to reach a voltage at which LED current starts flowing.
When the LED current reaches the amount of current, isolate the FB circuit from the SS circuit. With this, the startup
operation is completed.
After that, normal operation is controlled by following the feedback voltage of LED pins.
If the SS pin voltage reaches 4V or higher, the LED protection function will be activated to forcedly end the SS and FB
equalizing circuit.
www.rohm.com
© 2013 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
12/27
TSZ02201-0F1F0C100310-1-2
31.Jan.2014 Rev.002
http://www.Datasheet4U.com

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