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PDF PT4205 Data sheet ( Hoja de datos )
| Número de pieza | PT4205 | |
| Descripción | 1.2A Step-down HB LED Driver | |
| Fabricantes | PowTech | |
| Logotipo |  |
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PT4205
30V, 1.2A Step-down HB LED Driver
GENERAL DESCRIPTION
The PT4205 is a continuous conduction mode inductive
step-down converter, designed for driving single or
multiple serie connected LEDs efficiently from a
voltage source higher than the total LED chain voltage.
The device operates from an input supply between 5V
and 30V and provides an externally adjustable output
current of up to 1.2A. Depending upon the supply
voltage and external components, the PT4205can
provide more than tens of watts of output power.
The PT4205 includes the power switch and a high-side
output current sensing circuit, which uses an external
resistor to set the nominal average output current, and a
dedicated DIM input accepts either a DC voltage or a
wide range of pulsed dimming. Applying a voltage of
0.3V or lower to the DIM pin turns the output off and
switches the device into a low current standby state.
The PT4205 is available in SOT89-5 and ESOP8
packages.
ORDERING INFORMATION
FEATURES
Simple low parts count
Wide input voltage range: 5V to 30V
Up to 1.2A output current
Single pin on/off and brightness control using DC
voltage or PWM
Typical 3% output current accuracy
Inherent open-circuit LED protection
High efficiency (up to 97%)
Hysteretic Control: No Compensation
Adjustable Constant LED Current
Soft over temperature protection
ESOP8 package for large output power application
RoHS compliant
APPLICATIONS
Low voltage halogen replacement LEDs
Automotive lighting
LED back-up lighting
Illuminated signs
PACKAGE
SOT89-5
TEMPERATURE ORDERING PART
RANGE
NUMBER
-40 oC to 85 oC
PT4205E89E
ESOP8
-40 oC to 85 oC
PT4205EESH
Note:
xxxxxX
Assembly Factory Code
Lot Number
TYPICAL APPLICATION CIRCUIT
TRANSPORT
MEDIA
Tape and Reel
1000 units
Tape and Reel
2500 units
MARKING
PT4205
xxxxxX
PT4205
xxxxxX
VIN
DC5-30V
AC12-
18V
RS
0.28Ω
D
LED
3W
L=47uH
54
CIN 100uF
VIN CSN
PT4205
SW GND DIM
1 23
China Resources Powtech (Shanghai) Limited
PT4205_DS Rev EN_1.2
WWW.CRPOWTECH.COM
Page 1
1 page  
PT4205
30V, 1.2A Step-down HB LED Driver
OPERATION DESCRIPTION
The device, in conjunction with the coil (L1) and
current sense resistor (RS), forms a self oscillating
continuous-mode buck converter.
When input voltage VIN is first applied, the initial
current in L1 and RS is zero and there is no output from
the current sense circuit. Under this condition, the
output of CS comparator is high. This turns on an
internal switch and switches the SW pin low, causing
current to flow from VIN to ground, via RS, L1 and the
LED(s). The current rises at a rate determined by VIN
and L1 to produce a voltage ramp (VCSN) across RS.
When (VIN-VCSN) > 230mV, the output of CS
comparator switches low and the switch turns off. The
current flowing on the RS decreases at another rate.
When (VIN-VCSN) < 170mV, the switch turns on again
and the mean current on the LED is determined by
I OUT
0.17 0.23
2 Rs
0.2 / Rs .
The high-side current-sensing scheme and on-board
current-setting circuitry minimize the number of
external components while delivering LED current with
±3% accuracy, using a 1% sense resistor.
The PT4205 allow dimming with a PWM signal at the
DIM input. A logic level below 0.3V at DIM forces
PT4205 to turn off the LED and the logic level at DIM
must be at least 2.5V to turn on the full LED current.
The frequency of PWM dimming ranges from 100Hz to
more than 20 kHz.
The DIM pin can be driven by an external DC voltage
(VDIM) to adjust the output current below the nominal
average value defined by RS. The DC voltage is valid
from 0.5V to 2.5V. When the dc voltage is higher than
2.5V, the output current keeps constant. The LED
current also can be adjusted by a resistor connected to
the DIM pin. An internal pull-up current source is
connected to a 5V internal regulator. Connect a resistor
to DIM and GND sets the voltage of DIM:
VDIM=20uA*RDIM.
The DIM pin is pulled up to the internal regulator (5V)
by a current source. It can be floated at normal
operation. When a voltage applied to DIM falls below
the threshold (0.3V nom.), the switch is turned off. The
internal regulator and voltage reference remain
powered during shutdown to provide the reference for
the shutdown circuit. Quiescent supply current during
shutdown is nominally 130uA and switch leakage is
below 5uA.
Additionally, to ensure the reliability, the PT4205 is
built with a thermal shutdown (TSD) protection and a
thermal pad. The TSD protests the IC from over
temperature, when junction temperature more than
135 ℃ the output current begin to decrease
until to zero at 150℃. With the analog dimming
function via DIM pin, LED over temperature can easily
be realized by connecting a NTC resistor to DIM pin
and GND.
China Resources Powtech (Shanghai) Limited
PT4205_DS Rev EN_1.2
WWW.CRPOWTECH.COM
Page 5
5 Page 
PT4205
30V, 1.2A Step-down HB LED Driver
APPLICATION NOTES
Setting nominal average output current with
external resistor RS
The nominal average output current is determined by
the value of the external current sense resistor (RS)
connected between VIN and CSN and is given by:
IOUT 0.2 / Rs (Rs 0.17)
This equation is valid when DIM pin is float or applied
with a voltage higher than 2.5V (must be less than 5V).
Actually, RS sets the maximum average current which
can be adjusted to a less one by dimming.
Output current adjustment by external DC control
voltage
The DIM pin can be driven by an external dc voltage
(VDIM), as shown, to adjust the output current to a
value below the nominal average value defined by RS.
RS
VIN
0.28Ω
LED
3W
L
D 68uH
I
OUT
0.2
Rs
D
(0 D 100%,2.5V Vpulse 5V )
I OUT
Vpulse 0.2 D
2.5 Rs
(0 D 100%,0.5V Vpulse 2.5V )
RS
VIN
0.28Ω
LED
3W
L
D 68uH
VIN CSN SW
DIM PT4205
GND
VIN CSN SW
DIM PT4205
GND
The average output current is given by:
I OUT
0.0935 VDIM
2.5 Rs
(0.5V VDIM
1.9V )
I OUT
0.071 VDIM 1.9
Rs 0.6
(1.9V
VDIM
2.5V )
Note that 100% brightness setting corresponds to:
(2.5V VDIM 5V )
Output current adjustment by PWM control
A Pulse Width Modulated (PWM) signal with duty
cycle PWM can be applied to the DIM pin, as shown
below, to adjust the output current to a value below the
nominal average value set by resistor RS:
PWM dimming provides reduced brightness by
modulating the LED’s forward current between 0% and
100%. The LED brightness is controlled by adjusting
the relative ratios of the on time to the off time. A 25%
brightness level is achieved by turning the LED on at
full current for 25% of one cycle. To ensure this
switching process between on and off state is invisible
by human eyes, the switching frequency must be
greater than 100 Hz. Above 100 Hz, the human eyes
average the on and off times, seeing only an effective
brightness that is proportional to the LED’s on-time
duty cycle. The advantage of PWM dimming is that the
forward current is always constant, therefore the LED
color does not vary with brightness as it does with
analog dimming. Pulsing the current provides precise
brightness control while preserving the color purity.
The dimming frequency of PT4205 can be as high as 20
kHz.
Shutdown mode
Taking the DIM pin to a voltage below 0.3V will turn
off the output and the supply current will fall to a low
standby level of 130μA nominal.
China Resources Powtech (Shanghai) Limited
PT4205_DS Rev EN_1.2
WWW.CRPOWTECH.COM
Page 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet PT4205.PDF ] | |
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