EC4304BNB6R [E-CMOS]
PWM Control 1.2A Step-Down Converter;
| 型号： | EC4304BNB6R |
| 厂家： | 
E-CMOS Corporation |
| 描述： | PWM Control 1.2A Step-Down Converter |
| 文件： | 总11页 (文件大小：212K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PWM Control 1.2A Step-Down Converter EC4304B
FEATURES
GENERAL DESCRIPTION
• Wide Input Voltage Range: 7V to 36V
• LED Output Current Up to 1.2A
• Soft-start
• Single pin on/off and brightness control using
DC voltage or PWM
The EC4304B 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 7V and 36V and
provides an externally adjustable output
current of up to 1.2A. Depending upon supply
voltage and external components, this can
provide up to 42 watts of output power. The
EC4304B 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
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
• High efficiency (up to 97%)
• Up to 1MHz switching frequency
• Typical 5% output current accuracy
• SOT-23, SOT-89 Lead-free Package .
Applications
• LED/Display Back Light Driver
• Lightings
• Portable Communication Devices
• Handheld Electronics
frequency, this will provide either
a
continuous or a gated output current. The
PWM filter components are contained within
the chip. The EC4304B is available in SOT-23,
SOT-89 Lead-free package.
PART NUMBER EXAMPLES
PART NO.
EC4304BNB2R
EC4304BNB6R
PACKAGE
SOT-23-5
SOT-89-5
PIN ARRANGEMENT(Top view)
EC4304BNB2R
SOT-23-5
EC4304BNB6R
SOT-89-5
E-CMOS Corp. (www.ecmos.com.tw)
Page 1 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
PIN DESCRIPTION
DESCRIPTION
SOT-23 SOT-89
SYMBO
LX
1
2
1
2
Drain of NDMOS switch
Ground
GND
Multi-function On/Off and brightness control pin:
• Leave floating for normal operation.(VADJ = VREF = 1.25V giving
nominal average output current IOUTnom = 0.1/RS)
• Drive with DC voltage (0V < VADJ < 2.5V) to adjust output current
from 0% to 200% of IOUTnom
ADJ
3
3
• Drive with PWM signal from open-collector or open-drain transistor, to
adjust output current. Adjustment range 0% to 100% of IOUTnom for
f >10kHz and 0% to 100% of IOUTnom for f < 500Hz
Connect resistor RS from this pin to VIN to define nominal average output
current IOUTnom = 0.1/RS
ISENS
VIN
4
4
5
Input voltage (7V to 30V). Decouple to ground with 10uF or higher
5
X7R ceramic capacitor close to device
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Value
-0.3 to +36
-5 to +0.3
-0.3 to +6
-40 to +125
300
Unit
Voltage on intput pin relative to GND
ISENSE pin Voltage
VIN
V
V
V
C
C
C
ADJ and EN pin Voltage
Operating Temperature Rang
Maximum Soldering Temperature (at leads, 10 sec)
Storage Temperature Rang
T
A
T
LEAD
T
S
-65 to +150
SOT-23
SOT-89
SOT-23
SOT-89
0.35
0.5
Power Dissipation, PD @ TA = 25°C
Package Thermal Resistance, θJA
W
250
200
°C/W
E-CMOS Corp. (www.ecmos.com.tw)
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PWM Control 1.2A Step-Down Converter EC4304B
Electrical Characteristics (TA = -40 to 85°C unless otherwise noted. Typical values are at TA =25°C, VDD =12V)
Symbol
Description
Conditions
Min. Typ. Max Unit
VIN
Input Voltage
7
-
30
V
V
V
Internal regulator start-up threshold
Internal regulator shutdown
VIRU
VIN rising
VIN falling
5.65
5.55
VIRD
Quiescent supply current
with output off
IQOFF
IQON
EN pin grounded
35
uA
Quiescent supply current
with output switching
ADJ pin floating
f = 250kHz
1.8 5.0
mA
Measured on ISENSE pin with respect to
(Defines LED current setting accuracy) VIN, VADJ = 1.25V
Mean current sense threshold Voltage
VSENSE
95 100 105 mV
Sense threshold hysteresis
VSENTH
ISENSE
±15
10
%
uA
ISENSE pin input current
VSENSE =VIN – 0.1
Internal reference voltage
Temperature coefficient of VREF
Measured on ADJ pin with pin floating
VREF
1.25
50
V
∆VREF/∆T
ppm/K
External control voltage range on
ADJ pin for DC brightness control*
VADJ
0
2
2.5
V
V
VIHEN EN Input Voltage Hight
EN Input Voltage Low
VILEN
RADJ
ILXM
RLX
0.5
1.2
V
Kohm
A
Resistance between ADJ pin and VREF
Continuous LX switch current
LX Switch ‘On’ resistance
0< VADJ < 2.5V
@ ILX = 1.2 A
200
0.3 0.45 ohm
LX switch leakage current
ILXI
5
uA
C
TTP
Thermal Shutdown Protect
160
Electrical Characteristics (continuous)
Duty cycle range of PWM signal
applied to ADJ pin during low
frequency PWM dimming mode
PWM frequency<500Hz
PWM amplitude = VREF
Measured on ADJ pin
0.01
0.16
1
DPWML
Brightness control range
100:1
Duty cycle range of PWM signal
applied to ADJ pin during high
frequency PWM dimming mode
PWM frequency>10KHz
PWM amplitude = VREF
Measured on ADJ pin
1
DPWMH
Brightness control range
5:1
ADJ pin floating, L = 33uH (0.093 ohm)
IOUT=1A @VLED = 3.6V Driving 1 LED
fLX
280
KHz
Operating frequency
Minimum switch ‘ON’ time
Minimum switch ‘OFF’ time
LX switch ‘ON’
LX switch ‘OFF’
ns
ns
TONmin
TOFFmin
240**
200**
Recommended minimum switch 'ON'
time
TONminR
fLXmax
LX switch ‘ON’
800
ns
Recommended maximum operating
frequency
MHz
1
Recommended duty cycle range of
DLX
0.3
0.7
f
output switch at LXmax
50
ns
TPD
Internal comparator propagation delay
E-CMOS Corp. (www.ecmos.com.tw)
Page 3 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
Notes :
*100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the
VSENSE. threshold and output current proportionally.
**Parameters are not tested at production. Parameters are guaranteed by design, characterization and
process control.
Block Diagram
V
C C
D 1
L E D
L 1
R S
L X
V I N
M N
V
r e f.
R 1
C 1
4 . 7 u F
B u ffe r
-
+
R 4
-
A D J
E N
D r iv e r
+
V o lt a g e
r e g u la t o r
R 2
I n t e r n a l
V D D
B a n d
g a p
O v e r
T e m p .
R 3
G N D
E-CMOS Corp. (www.ecmos.com.tw)
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PWM Control 1.2A Step-Down Converter EC4304B
Functional Description
The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a selfoscillating
continuous-mode buck converter.
Device operation
Operation can be best understood by assuming that the ADJ pin of the device is unconnected
and the voltage on this pin (VADJ) appears directly at the (+) input of the comparator.
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 (-) input to the comparator is
at ground and its output is high. This turns MN on and switches the LX 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 (VSENSE) across RS. The supply referred voltage VSENSE is
forced across internal resistor R1 by the current sense circuit and produces a proportional current
in internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of
the comparator. When this reaches the threshold voltage (VADJ), the comparator output switches
low and MN turns off. The comparator output also drives another NMOS switch, which
bypasses internal resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by
R3 to be nominally 15% of VADJ.
When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to VIN. The
current decays at a rate determined by the LED(s) and diode forward voltages to produce a falling
voltage at the input of the comparator. When this voltage returns to VADJ, the comparator output
switches high again. This cycle of events repeats, with the comparator input ramping between
limits of VADJ ± 15%.
Switching thresholds
With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of
100mV (measured on the ISENSE pin with respect to VIN). The average output current IOUTnom is
then defined by this voltage and RS according to:
IOUTnom = 100mV/RS
Nominal ripple current is ±15mV/RS
Adjusting output current
The device contains a low pass filter between the ADJ pin and the threshold comparator and an
internal current limiting resistor (200kohn nom) between ADJ and the internal reference voltage.
This allows the ADJ pin to be overdriven with either DC or pulse signals to change the VSENSE
switching threshold and adjust the output current. The filter is third order, comprising three
sections, each with a cut-off frequency of nominally 4kHz. Details of the different modes of
adjusting output current are given in the applications section.
Output shutdown
The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit
falls below the threshold, the internal regulator and the output switch are turned off. The voltage
reference remains powered during shutdown to provide the bias current for the shutdown circuit.
Quiescent supply current during shutdown is nominally 35uA and switch leakage is below 5uA.
E-CMOS Corp. (www.ecmos.com.tw)
Page 5 of 11
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PWM Control 1.2A Step-Down Converter EC4304B
Applications Information
Setting nominal average output current with external resistor RS
The nominal average output current in the LED(s) is determined by the value of the external current
sense resistor (RS) connected between VIN and ISENSE and is given by:
IOUTnom = 0.1/RS [for RS ≥ 0.066 ohm]
The table below gives values of nominal average output current for several preferred values
of current setting resistor (RS) in the typical application circuit :
RS (ohm)
0.066
0.1
0.142
0.285
Nominal average
output current (mA)
1500
1000
700
350
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V).
Note that RS = 0.066ohm is the minimum allowed value of sense resistor under these conditions to
maintain switch current below the specified maximum value.
It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See
next section)
Output current adjustment by external DC control voltage
The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current
to a value above or below the nominal average value defined by RS.
ADJ
EC4304B
GND
+
DC
GND
The nominal average output current in this case is given by:
IOUTdc = (VADJ /1.25) x (0.1V / RS), [for 0 < VADJ <2.5V]
Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above
1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 1.5A maximum.
The input impedance of the ADJ pin is 200kohm ±25%.
Output current adjustment by PWM control
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as
shown below, to adjust the output current to a value above or below the nominal average value
set by resistor RS:
PWM
VADJ
ADJ
EC4304B
0V
GND
E-CMOS Corp. (www.ecmos.com.tw)
Page 6 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
Driving the ADJ input via open collector transistor
The recommended method of driving the ADJ pin and controlling the amplitude of the PWM
waveform is to use a small NPN switching transistor as shown below:
ADJ
PWM
EC4304B
GND
This scheme uses the 200k resistor between the ADJ pin and the internal voltage reference as
a pull-up resistor for the external transistor.
Driving the ADJ input from a microcontroller
Another possibility is to drive the device from the open drain output of a microcontroller. The
diagram below shows one method of doing this:
ADJ
MCU
EC4304B
GND
If the NMOS transistor within the microcontroller has high Drain / Source capacitance, this
arrangement can inject a negative spike into ADJ input of the EC4304B and cause erratic
operation but the addition of a Schottky clamp diode (cathode to ADJ) to ground and inclusion of a
series resistor (10K) will prevent this. See the section on PWM dimming for more details of the
various modes of control using high frequency and low frequency PWM signals.
Shutdown mode
Taking the EN pin to a voltage below 0.8V for more than approximately 100us, will turn off the
output and supply current will fall to a low standby level of 35uA nominal.
E-CMOS Corp. (www.ecmos.com.tw)
Page 7 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
Capacitor selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in
series with the supply source impedance and lowers overall efficiency. This capacitor has to supply
the relatively high peak current to the coil and smooth the current ripple on the input supply. A
minimum value of 47uF is acceptable if the input source is close to the device, but higher values
will improve performance at lower input voltages, especially when the source impedance is high. In
order to avoid high frequency noise influence and improve circuit stability, it is recommended to
shunt a value of 0.22uF Capacitor. The input capacitor should be placed as close as possible to the
IC. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better
dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this
application and should not be used.
Inductor selection
Recommended inductor values for the EC4304B are in the range 33uH to 100uH. Higher values of
inductance are recommended at higher supply voltages in order to minimize errors due to
switching delays, which result in increased ripple and lower efficiency. Higher values of
inductance also result in a smaller change in output current over the supply voltage range. The
inductor should be mounted as close to the device as possible with low resistance connections to
the LX and VIN pins. The chosen coil should have a saturation current 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 operating duty cycle and switch 'on'/'off'
times within the specified limits over the supply voltage and load current range.
LX switch on time : ton = L∆I / (VIN – VLED - Iavg (RS+rL+RLX)) , note: tonmin > 240ns
LX switch off time : toff = L∆I / (VLED + VD + Iavg (RS+rL)) , note: toffmin > 200ns
Where:
“L” is the coil inductance (H)
“∆I” is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}
“rL” is the coil resistance (ohm)
“RS” is the current sense resistance
“Iavg” is the required LED current (A)
“VIN” is the supply voltage (V)
“VLED” is the total LED forward voltage (V)
“RLX” is the switch resistance (ohm) {=0.3 ohm nominal}
“VD” is the diode forward voltage at the required load current (V)
E-CMOS Corp. (www.ecmos.com.tw)
Page 8 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
TYPICAL APPLICATION CIRCUITS
VIN 7V to 36V
RS 0.1 ohm
C1
47uF
LED
C2
0.22uF
L1
47uH
D1
* C3
0.1uF
* C4
1000PF
VIN
ADJ
ISENSE
LX
EC4304
NC
B
GND
* note : When outputs the big current, the noise are big, this and the system environment and PCB layout have
the influential, may defer to the actual need to increase the capacitor filtration noise.
E-CMOS Corp. (www.ecmos.com.tw)
Page 9 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
PACKAGE DIMENSIONS
SOT-23-5
B
B
1
B
2
A
1
A
C
1
C
C
2
F
D
G
E
H
I
Dimension in mm
Typ.
Dimension in inch
Typ.
Symbol
Min.
2.60
1.40
2.70
Max.
3.00
1.60
3.00
Min.
Max.
0.118
0.063
0.118
A
A1
B
2.80
1.575
2.85
0.102
0.055
0.106
0.110
0.062
0.112
B1
B2
C
C1
C2
D
1.90(BSC)
0.95(BSC)
1.20
0.075(BSC)
0.037(BSC)
0.047
0.95
0.90
0
1.45
1.30
0.150
0.037
0.035
0
0.057
0.051
0.06
1.10
0.075
0.40
0.043
0.003
0.015
E
F
0.30
0.08
0.45
0.15
0.60
0.22
0.012
0.003
0.018
0.006
0.023
0.009
G
0.60(REF)
0~8°
H
5~15°
5~15°
I
E-CMOS Corp. (www.ecmos.com.tw)
Page 10 of 11
2011/10/06
PWM Control 1.2A Step-Down Converter EC4304B
PACKAGE DIMENSIONS
SOT-89
D
POLISHED(2X)
E
L
H
3
1
2
B1
C
B
10'(2X)
A
e
e1
Dimension in mm
Dimension in inch
Symbol
Min.
1.40
0.44
0.36
0.35
4.40
2.29
3.94
Max.
1.60
0.56
0.48
0.44
4.60
2.60
4.25
Min.
Max.
0.063
0.022
0.019
0.017
0.181
0.102
0.167
A
B
B1
C
D
E
H
e
0.055
0.017
0.014
0.013
0.173
0.090
0.155
1.50 BSC
3.00 BSC
0.89
0.059 BSC
0.118 BSC
e1
L
1.2
0.035
0.047
*Note :
The thermal pad on the IC’s bottom has to be mounted on the copper foil.
To eliminate the noise influence, the thermal pad is suggested to be connected to GND on PCB. In
addition, desired thermal conductivity will be improved, if a heat-conducting copper foil on PCB is
soldered with thermal pad. The thermal pad enhances the power dissipation. As a result, a large
amount of current can be sunk safely in one package.
E-CMOS Corp. (www.ecmos.com.tw)
Page 11 of 11
2011/10/06
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