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PDF PAM2861 Data sheet ( Hoja de datos )
| Número de pieza | PAM2861 | |
| Descripción | 1A LED DRIVER | |
| Fabricantes | Power Analog Micoelectronics | |
| Logotipo |  |
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PAM2861
1A LED Driver with Internal Switch
Features
Description
n Simple low parts count
The PAM2861 is a continuous mode inductive
n Internal 40V NDMOS switch
step-down converter, designed for driving single
n 1A output current
or multiple series connected LEDs efficiently
n Single pin on/off and brightness control
from a voltage source higher than the LED
Using DC voltage or PWM
voltage. The device operates from an input
n Soft-start
supply between 6V and 40V and provides an
n High efficiency (up to 95%)
externally adjustable output current of up to 1A.
n Wide input voltage range: 6V to 40V
Depending upon supply voltage and external
n Output shutdown
components, this can provide up to 30 watts of
n Up to 1MHz switching frequency
output power.
n Inherent open-circuit LED protection
n Typical 5% output current accuracy
n Pb-free SOT23-5, SOT89-5 and PSOP-8
Packages
E TApplications
H En Low voltage halogen replacement LEDs
Sn Low voltage industrial lighting
An LED back-up lighting
A RY D ATn Illuminated signs
The PAM2861 includes the output switch and a
high-side output current sensing circuit, which
uses an external resistor to set the nominal
average output current.
Output current can be adjusted below the set
value, by applying an external control signal to
the VSET pin.
The VSET pin will accept either a DC voltage or a
PWM waveform.
The soft-start time can be increased using an
external capacitor from the VSET pin to ground.
Applying a voltage of 0.2V or lower to the VSET
pin turns the output off and switches the device
into a low current standby state.
PRELIMINTypical Application
D1
Rs
0.3Ω
VIN(6V-40V)
VIN
ISENSE
PAM2861
L1
100μH
C1
10μF
VSET
Floating
GND
LX
Power Analog Microelectronics,Inc
www.poweranalog.com
1
03/2010
1 page  
PAM2861
1A LED Driver with Internal Switch
Electrical Characteristic
TA=25°C, VIN=16V, unless otherwise noted.
Parameter
Symbol
Condition
Min Typ Max Units
Input voltage
Vin
6 40 V
Output current
ILED
RS=0.3Ω
RS=0.1Ω
333 mA
1A
Shutdown current
ISD VSET pin grounded
20 40 μA
Quiescent current without
switching
IQ VSET pin floating, Vin=16V 0.6 mA
Mean current sense threshold
voltage
TSense threshold hysteresis
EIsense pin input current
EVset range on VSET pin
S HDC voltage on VSET pin to enable
ADC voltage on VSET pin to disable
TLX switch on resistance
D ALX switch leakage current
Soft start time
RYOperating frequency
I N ARecommended minimum switch
ON time
I MRecommended maximum switch
Lfrequency
R EMax duty circle
PRecommended duty cycle range
Vsense
Vsense_hys
Isense
Ven
Venon
venoff
RLX
ILX(leak)
Ts s
FLX
Ton_rec
FLXmax
DLX
Measured on Isense pin with
respect to VIN
Vsense = Vin – 0.1
For DC dimming
Ven rising
Ven falling
@ILX=100mA
Vin=16V, Cen = 1nF
Vi=16V, Vo=9.6V (3 LEDS),
L=47μH, ΔI=0.25A (ILED=1A)
For 4% accuracy
95
0.4
25
100 105 mV
13
8
0.25
0.2
0.3
1.5
2.5
5
%
μA
V
V
V
Ω
μA
ms
233 kHz
500 ns
1.0 MHz
98 %
75 %
Internal comparator propagation
delay
TP D*
45 ns
Over temperature protection
TOTP
150 °C
Temp protection hysteresis
TO TP_hys
40 °C
Current limit
IXLmax
Peak inductor current
1.7 A
*parameters are not tested at production,but guaranteed by design.
Power Analog Microelectronics,Inc
www.poweranalog.com
5
03/2010
5 Page 
PAM2861
1A LED Driver with Internal Switch
Application Information
Setting nominal average output current with over the supply voltage range. The inductor should
external resistor RS
The nominal average output current in the LED(s)
be mounted as close to the device as possible with
low resistance connections to the LX and VIN pins.
is determined by the value of the external current The chosen coil should have a saturation current
sense resistor (RS) connected between VIN and
ISENSE and is given by:
The
table
b
e
l
o
IOUTnom =
w gives v
0.1
aRlSu
e
s
of
nominal
average
higher than the peak output current and a
continuous current rating above the required mean
output current.
The inductor value should be chosen to maintain
output current for several preferred values of operating duty cycle and switch 'on'/'off' times
current setting resistor (RS) in the typical
application circuit shown on page 1.
RS (Ω)
T0.1
E0.13
E0.15
H0.3
Nominal average output current (mA)
1000
760
667
333
SThe above values assume that the VSET pin is
Afloating and at a nominal voltage of VREF (1.25V).
TNote that RS = 0.1Ω is the minimum allowed value
Aof sense resistor under these conditions to
Dmaintain switch current below the specified
Ymaximum value. It is possible to use different
values of RS if the VSET pin is driven from an
Rexternal voltage.
I N ACapacitor selection
A low ESR capacitor should be used for input
I Mdecoupling, as the ESR of this capacitor appears
in series with the supply source impedance and
Llowers overall efficiency. This capacitor has to
Esupply the relatively high peak current to the coil
Rand smooth the current ripple on the input supply.
PA minimum value of 4.7μF is acceptable if the input
within the specified limits over the supply voltage
and load current range. The following equations
can be used as a guide.
LX Switch 'On' time
TON
=
VIN
-
VLED
LDI
- ILED (RS
+ RL
+ RLX )
LX Switch 'Off' time
TO F F
=
VLED
+
VD
LDI
+ ILED (R S
+ RL )
Where: L is the coil inductance; RL is the coil
resistance ; RS is the current sense resistance ILED
is the required LED current; ΔI is the coil peak-
peak ripple current (Internally set to 0.25 x I )LED ; VIN
is the supply voltage; VLED is the total LED forward
voltage; RLX is the switch resistance (0.3Ω
nominal); VD is the diode forward voltage at the
required load current.
Diode selection
For maximum efficiency and performance, the
rectifier (D1) should be a fast low capacitance
Schottky diode with low reverse leakage at the
maximum operating voltage and temperature.
They also provide better efficiency than silicon
source is close to the device, but higher values will diodes, due to a combination of lower forward
improve performance at lower input voltages, voltage and reduced recovery time.
especially when the source impedance is high.
The input capacitor should be placed as close as It is important to select parts with a peak current
possible to the IC.
rating above the peak coil current and a
continuous current rating higher than the
For maximum stability over temperature and maximum output load current. It is very important
voltage, capacitors with X7R, X5R, or better to consider the reverse leakage of the diode when
dielectric are recommended. Capacitors with Y5V operating above 85°C. Excess leakage will
dielectric are not suitable for decoupling in this increase the power dissipation in the device and if
application and should NOT be used.
close to the load may create a thermal runaway
condition.
Inductor selection
Recommended inductor values for the PAM2861 The higher forward voltage and overshoot due to
are in the range 33μH to 100μH. Higher values of reverse recovery time in silicon diodes will
inductance are recommended at higher supply increase the peak voltage on the LX output. If a
voltages in order to minimize errors due to silicon diode is used, care should be taken to
switching delays, which result in increased ripple ensure that the total voltage appearing on the LX
and lower efficiency. Higher values of inductance pin including supply ripple, does not exceed the
also result in a smaller change in output current specified maximum value.
Power Analog Microelectronics,Inc
www.poweranalog.com
11
03/2010
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet PAM2861.PDF ] | |
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