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PDF PT6903 Data sheet ( Hoja de datos )
| Número de pieza | PT6903 | |
| Descripción | High Brightness LED Driver | |
| Fabricantes | PTC | |
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超航國際有限公司
High Brightness LED Driver
Tel: 886-2-26311112
Fax: 886-2-26340690
URL:http://www.exin.com.tw
Preliminary
PT6903
DESCRIPTION
PT6903 is a PFM high brightness LED driver control IC. It allows efficient operation of driver current up
to 1.0A output, and the input range is from 7V to 36V. Moreover, PT6903 controls the internal MOS at
a modulated switch frequency up to 1MHz. PT6903 drives a single or multiple series
LEDs at a constant-current control method; thus, providing constant current light output and enhance
PT6903 has linear and PWM dimming functions. Output current to an LED string can be programmed
to any value between its minimum value to its maximum value at the linear dimming control input of
PT6903. PT6903 provides a low-frequency PWM dimming input that can accept an external control
signal with a duty cycle of 0~100% and a frequency between 100Hz and a few KHz.
PT6903 integrates more protection functions. The reliability of LEDs and device can be promoted by
these protection functions. PT6903 provides over current protection when output short-circuit or LEDs
current rises up about two times setting current. PT6903 must be power-up again if
over current protection happens. PT6903 also provides over temperature protection. There are two
ways to protect LEDs and device when temperature rises up to limited level. One is internal thermal-
shutdown function.
If internal temperature rises up about 135 , PT6903 will turn off switch. It will turn-on again when
internal temperature falls down about 115 . Another is temperature compensation
function. This function is only used for SOP8 package. An NTC thermistor temperature monitoring
240mV and LED current will fall under value. This function can reduce the temperature
setting
FEATURES
• >90% Efficiency
• Wide input voltage range: 7V to 36V
• Constant current driver
• Applications up to 1.0A
• Linear & PWM dimming
• Thermal shutdown protection
• Over current protection
• Internal 40V power NMOS switch
APPLICATIONS
• DC/DC LED driver
• Low voltage industrial LED lighting
• Low voltage halogen replacement LEDs
• Decorative LED lighting
PT6903 PRE1.3
-1-
September, 2008
1 page  
High Brightness LED Driver
Preliminary
PT6903
LD (PIN8): Linear Dimming. LD pin is only used in SOP-8 package. It will be disabling if the voltage
on this pin is larger than 240mV typical. So, this pin should be connected to VDD pin if linear dimming
is not need. If the voltage on this pin is less than 240mV, the peak current of LEDs string will be
determined by both the voltage of LD and CS resistor. The peak current of LEDs string under linear
dimming can be calculated by following formula:
I PK
= VLD
RCS
OPERATION
The PT6903 is optimized to drive buck LED drivers using open-loop peak current mode control. This
architecture enables fairly accurate LED current control without the need for high side current sensing
or the design of any closed loop controllers. The PT6903 uses very few external components and
enables both linear and PWM dimming of the LED current. A resistor connected to
the RT pin programs the off-time of power switch. The oscillator produces pulses at regular
intervals. The same pulses also start the blanking timer which inhibits the reset input of the SR flip-
flop and prevent false turn-offs due to the turn-on spike. When the switch turns on, the current
through the inductor starts ramping up. This current flows through the external sense resistor RCS and
produces a ramp voltage at
the CS pin. The internal comparators are constantly comparing the CS pin voltage to both the voltage
at the LD pin and the internal 240mV. Once the blanking timer is complete, the
output of these comparators is allowed to reset the flip-flop. When the output of either one of the two
comparators goes high, the flip-flop is reset and the power switch turns-off. The switch turns-on until
The PT6903 is a fixed off-time control LED driver. The off-time of power switch is only set by RT
resistor. But the on-time of power switch is set by more factors such as input supply voltage, loading,
inductor. So, the frequency is a dynamitic change by these factors. The fixed off-time peak current
control scheme can easily operate at duty cycles greater than 0.5 and also gives inherent input voltage
rejection making the LED current almost insensitive to input voltage variations.
PT6903 PRE1.3
-5-
September, 2008
5 Page 
High Brightness LED Driver
Preliminary
PT6903
BOARD LAYOUT
The high speed operation of the PT6903 demands careful attention to board layout and component
placement. The exposed pad (for TO-252-5L) of the package is the only GND terminal of the IC and is
also important for thermal management of the IC. It is crucial to achieve a good electrical and thermal
contact between the exposed pad and the ground plane of the board. To reduce
electromagnetic interference (EMI), it is important to minimize the area of the SW node. Use a GND
plane under SW and minimize the length of traces in the high frequency switching path between SW
and GND through
The bypass capacitor on the VIN supply to the PT6903 should be placed as close as possible to the
VIN terminal of the device.
To minimize ground ‘bounce’, the CS sense resistor should be separated from the GND of IC and
soldered directly to the ground plane.
It is also important to minimize any track resistance in series with CS sense resistor RCS. It’s best to
connect CS directly to one end of RCS and ground plane directly to the opposite end of RCS with no
other currents flowing in these tracks.
PT6903 PRE1.3
- 11 -
September, 2008
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet PT6903.PDF ] | |
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