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PDF MT7201 Data sheet ( Hoja de datos )
| Número de pieza | MT7201 | |
| Descripción | 1A LED driver | |
| Fabricantes | Maxic Technology | |
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MT7201
1A LED driver with internal switch
DESCRIPTION
The MT7201 is a continuous mode inductive
step-down converter, designed for driving
single or multiple series connected LEDs
efficiently from a voltage source higher than
the LED voltage. The device operates from an
input supply between 7~40V and provides an
externally adjustable output current of up to 1A.
Depending upon supply voltage and external
components, this can provide up to 32 watts of
output power.
The MT7201 includes the output switch and a
high-side output current sensing circuit, which
uses an external resistor to set the nominal
average output current.
FEATURES
Pass 4KV ESD test
Simple low parts count
1A output current
Single pin on/off and brightness control
using DC voltage or PWM
Internal PWM filter
Soft-start
High efficiency (up to 97%)
Wide input voltage range: 7V to 40V
Output shutdown
Up to 1MHz switching frequency
Inherent open-circuit LED protection
Typical 2% output current accuracy
PIN CONFIGURATION
LX 1
5 VIN
GND 2
SOT89-5
ADJ 3
4 ISENSE
Output current can be adjusted above, or
below the set value, by applying an external
control signal to the 'ADJ' pin.
The ADJ pin will accept either a DC voltage or
a PWM waveform. Depending upon the control
frequency, this will provide either a continuous
or a gated output current. The PWM filter
components are contained within the chip.
The PWM filter provides a soft-start feature by
controlling the rise of input/output current. The
soft-start time can be increased using an
external capacitor from the ADJ pin to ground.
Applying a voltage of 0.2V or lower to the ADJ
pin turns the output off and switches the
device into a low current standby state.
The device is assembled in a SOT89-5 pin
package.
APPLICATION
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
APPLICATION CIRCUIT
47μH
0.1Ω
VIN ISENSE
MT7201 4.7μF
LX GND ADJ
(Top view)
MT7201 Rev. 1.5
www.maxictech.com
Copyright © 2008 Maxic Technology Corporation
Page 1
1 page  
MT7201
1A LED driver with internal switch
Typical operating conditions
1.05
1.04
1.03
1.02
1.01
1
0.99
0.98
0.97
0.96
0.95
1
Output Current (Vin=12V)
2
Number of LEDs
33uH
47uH
100uH
3
5.000%
4.000%
3.000%
2.000%
1.000%
0.000%
‐1.000%
‐2.000%
‐3.000%
‐4.000%
‐5.000%
1
Current Variation(Vin=12V)
2
Number of LEDs
33uH
47uH
100uH
3
Output Current (Vin=24V)
1.1
1.05
1
0.95
0.9
3
33uH
47uH
100uH
456
Number of LEDs
7
5.000%
4.000%
3.000%
2.000%
1.000%
0.000%
‐1.000%
‐2.000%
‐3.000%
‐4.000%
‐5.000%
3
Current Variation(Vin=24V)
33uH
47uH
100uH
456
Number of LEDs
7
Output Current (Vin=36V)
1.14
1.12
1.1
1.08
1.06
1.04
1.02
1
5
33uH
47uH
100uH
6789
Number of LEDs
10
5.000%
4.000%
3.000%
2.000%
1.000%
0.000%
‐1.000%
‐2.000%
‐3.000%
‐4.000%
‐5.000%
5
Current Variation(Vin=36V)
33uH
47uH
100uH
6789
Number of LEDs
10
MT7201 Rev. 1.5
www.maxictech.com
Copyright © 2008 Maxic Technology Corporation
Page 5
5 Page 
MT7201
1A LED driver with internal switch
TOFF
VD
LΔI
VLED I RS
rL
Note: TOFFmin>200ns
Where:
L is the coil inductance (H)
rL is the coil resistance (Ω)
Iavg is the required LED current (A)
ΔI is the coil peak-peak ripple current (A)
{internally set to 0.3 x Iavg}
VIN is the supply voltage (V)
VLED is the total LED forward voltage (V)
RLX is the switch resistance (Ω)
VD is the diode forward voltage at the required
load current (V)
the device will start to operate. However, with
the supply voltage below the specified
minimum value, the switch duty cycle will be
high and the device power dissipation will be
at a maximum. Care should be taken to avoid
operating the device under such conditions in
the application, in order to minimize the risk of
exceeding the maximum allowed die
temperature.
Note that when driving loads of two or more
LEDs, the forward drop will normally be
sufficient to prevent the device from switching
below approximately 6V. This will minimize the
risk of damage to the device.
Diode selection
It is important to select parts with a peak
current rating above the peak coil current and
a continuous current rating higher than the
maximum output load current. It is very
important to consider the reverse leakage of
the diode when operating above 85°C. Excess
leakage will increase the power dissipation in
the device.
Reducing output ripple
Peak to peak ripple current in the LED can be
reduced, if required, by shunting a capacitor
Cled across the LED(s), A value of 1μF will
reduce nominal ripple current by a factor three
(approx.). Proportionally lower ripple can be
achieved with higher capacitor values. Note
that the capacitor will not affect operating
frequency or efficiency, but it will increase
start-up delay, by reducing the rate of rise of
LED voltage.
Operation at low supply voltage
The internal regulator disables the drive to the
switch until the supply has risen above the
startup threshold (VSU). Above this threshold,
Layout considerations
LX pin
The LX pin of the device is a fast switching
node, so PCB tracks should be kept as short
as possible. To minimize ground 'bounce', the
ground pin of the device should be soldered
directly to the ground plane.
Coil and decoupling capacitors and current
sense resistor
It is particularly important to mount the coil and
the input decoupling capacitor as close to the
device pins as possible to minimize parasitic
resistance and inductance, which will degrade
efficiency. It is also important to minimize any
track resistance in series with current sense
resistor RS. It’s best to connect VIN directly to
one end of RS and Isense directly to the
opposite end of RS with no other currents
flowing in these tracks. It is important that the
cathode current of the Schottky diode does not
flow in a track between RS and VIN as this may
give an apparent higher measure of current
than is actual because of track resistance.
MT7201 Rev. 1.5
www.maxictech.com
Copyright © 2008 Maxic Technology Corporation
Page 11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MT7201.PDF ] | |
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