|
|
PDF HT7937 Data sheet ( Hoja de datos )
| Número de pieza | HT7937 | |
| Descripción | Built-in OVP White LED Step-up Converter | |
| Fabricantes | Holtek Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de HT7937 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
|
No Preview Available !
HT7937
Built-in OVP White LED Step-up Converter
Features
· Integrated open-circuit protection
· Over voltage protection
· Up to 84% efficiency at VIN=3V, 3LEDs,
ILED= 20mA
· 1.2MHz fixed switching frequency
· Low standby current: 0.1mA (typ.) (VSHDN=0V)
· Matches LED current
· Small value inductor and capacitors
· Small outline SOT23-6 package
Applications
· Cellular phones
· PDAs
· DSCs
· Handheld devices
· White LED display backlighting
General Description
The HT7937 is high efficiency boost converter with a
constant current output to provide back light functions in
handheld devices. Applications with series connected
LEDs ensure constant and identical LED currents re-
sulting in uniform brightness. A continuous LED output
current is setup using the FB pin regulated voltage
across an external sense resistor, RFB connected be-
tween the FB pin and ground. The integrated open load
protection circuitry prevents damage resulting from an
Block Diagram
open circuit condition. The low 95mV feedback voltage
minimises power losses in the current setting resistor
which improves efficiency. The HT7937 has a high
switching frequency of up to 1.2MHz which permits the
use of lower value extremely small outline inductor and
filter capacitor.
The HT7937 is supplied in a space-saving, 6-lead
SOT23-6 package type.
www.DataSheet4U.com
SHDN
FB
28V
C o n tro l
L o g ic
O VP
SW
95m V
å
1 .2 M H z
O s c illa to r
GND
V IN
Rev 1.10
1 January 18, 2010
1 page  
HT7937
Component Selection
· Setting the LED Current
The step-up converter regulates the LED current by
regulating the voltage across the current sense resis-
tor, RFB. To ensure the generation of accurate LED
currents, it is recommended that a precision resistor is
used for RFB. The voltage across the sense resistor is
regulated to the internal reference voltage of 95mV.
The LED current is calculated using the following
equation:
ILED
VFB
RFB
Where
VFB = Feedback voltage is 95mV
· Inductor Selection
The selected inductor must have a saturation current
greater than the maximum peak current of the step-up
converter. A recommended value of inductor for 3 to 6
white LED applications is 4.7mH to 22mH. For good ef-
ficiency the inductor should have low core loss and
low DCR (DC Resistance).
The peak inductor current is calculated using the
following equation:
Where
VO = Output Voltage
Vi = Input Voltage
IO = Output Current
h = Efficiency
L = Inductance
FS = Switching Frequency is 1.2MHz
· Diode Selection
The diode must have a rating greater than the output
voltage and output current. In switching applications
both forward voltage drop and diode capacitance are
www.DataSheet4U.cimomportant considerations.
A Schottky diode is used due to its low forward voltage
drop and fast switching speeds which improves effi-
ciency. The Schottky diode has average current of IO,
and a peak current which is the same as the inductor¢s
peak current and a voltage rating at least 1.5 times the
output voltage. A recommended Schottky diode type
is the 1N5819.
· Capacitor Selection
A low ESR (Equivalent Series Resistance) capacitor
should be used for the input/output capacitors to mini-
mize ripples. Both X5R and X7R types are suitable
due to their wider voltage and temperature ranges. In-
put and output ceramic capacitors of 1mF are recom-
mended for HT7937 applications.
The output ripple voltage is calculated as the following
equation:
Where
IL(PEAK) = Peak Inductor Current
CO(ESR) = Output Capacitor¢s Equivalent Series
Resistance
IO = Output Current
VO = Output Voltage
Vi = Input Voltage
CO = Output Capacitance
FS = Switching Frequency is 1.2MHz
Layout Considerations
Circuit board layout is a very important consideration for
switching regulators if they are to function properly. Poor
circuit layout may result in related noise problems.
In order to minimise EMI and switching noise, please fol-
low the guidelines below:
· All tracks should be as wide as possible.
· The input and output capacitors, C1 and C2, should
be placed close to the VIN, VOUT and GND pins.
· The Schottky diode, D1, and inductor, L1, must all be
placed close to the SW pin.
· Feedback resistor, R1, must be placed close to the FB
and GND pins.
· A full ground plane is always helpful for better EMI
performance.
A recommended PCB layout with component locations
is shown below.
Top Layer
Bottom Layer
Rev 1.10
5 January 18, 2010
5 Page 
Product Tape and Reel Specifications
Reel Dimensions
T2
D
HT7937
AB
C
T1
SOT23-6
Symbol
A
B
C
D
T1
T2
www.DataSheet4U.com
Description
Reel Outer Diameter
Reel Inner Diameter
Spindle Hole Diameter
Key Slit Width
Space Between Flange
Reel Thickness
Dimensions in mm
178.0±1.0
62.0±1.0
13.0±0.2
2.50±0.25
8.4+1.5/-0.0
11.4+1.5/-0.0
Rev 1.10
11 January 18, 2010
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet HT7937.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| HT7936A | White LED Step-up Charge Pump Converter | Holtek Semiconductor |
| HT7936B | White LED Step-up Charge Pump Converter | Holtek Semiconductor |
| HT7937 | Built-in OVP White LED Step-up Converter | Holtek Semiconductor |
| HT7938 | High Current And Performance White LED Driver | Holtek Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |