PT4211
30V 350mA Step-down HB LED Driver
GENERAL DESCRIPTION
FEATURES
The PT4211 is a continuous conduction mode inductive
step-down converter, designed for driving single or
multiple series connected LEDs from a voltage source
higher than the LED voltage. The device operates from
an input supply between 5V and 30V and provides an
externally adjustable output current of up to 350mA.
The PT4211 includes the output 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 a wide range of pulsed
dimming. Applying a voltage of 0.4V or lower to the
DIM pin turns the output off and switches the device
into a low current standby state. Built-in Soft Over
Temperature Protection protects the device from over
temperature damage.
Simple low parts count
Wide input voltage range: 5V to 30V
Up to 350mA output current
PWM dimming
3% output current accuracy.
Up to 1MHz switching frequency
Typical 3% output current accuracy
Inherent open-circuit LED protection
High efficiency (up to 93%)
Adjustable Constant LED Current
High-Side Current Sense
Hysteretic Control: No Compensation
Soft Over Temperature Protection
APPLICATION
Low voltage halogen replacement LEDs
Automotive lighting
LED back-up lighting
Illuminated signs
The PT4211 is available in SOT23-5 package.
ORDERING INFORMATION
TEMPERATURE
ORDERING PART
TRANSPORT
RANGE
NUMBER
MEDIA
SOT23-5
-40 oC 到 85 oC
PT4211E23E
SOT23-5
-40 oC 到 85 oC
PT4211F23E
PACKAGE
MARKING
Tape and Reel
4211
3000 units
Tape and Reel
4211
3000 units
TYPICAL APPLICATION CIRCUIT
RS
VIN
0.58Ω
DC5-30V
LED
D
3*1W
L=47uH
L
AC1218V
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
CIN
5
4
100uF
VIN
CSN
PT4211
SW
GND
1
2
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DIM
3
Page1
PT4211
30V 350mA Step-down HB LED Driver
PIN ASSIGNMENT
VIN
CSN
5
4
4211
PIN DESCRIPTIONS
1
2
3
SW
GND
DIM
ESOP8
PIN No.
PIN NAMES
DESCRIPTION
1
SW
Switch Output. SW is the drain of the internal N-Ch MOSFET switch.
2
GND
3
DIM
4
CSN
Current sense input
5
VIN
Input Supply Pin. Must be locally bypassed.
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
Signal and power ground. Connect directly to ground plane.
Logic level dimming input. Drive DIM low to turn off the current
regulator. Drive DIM high to enable the current regulator.
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PT4211
30V 350mA Step-down HB LED Driver
ABSOLUTE MAXIMUM RATINGS (note1)
SYMBOL
ITEMS
VALUE
UNIT
VIN
Supply Voltage
-0.3~40
V
SW
Drain of the internal power switch
-0.3~40
V
CSN
Current sense input (Respect to VIN)
+0.3~(-6.0)
V
DIM
Logic level dimming input
-0.3~5.5
V
PDMAX
Power Dissipation (Note 2)
260
θJA
PTR
Thermal Resistance, SOT23-5
TJ
Operation Junction Temperature Range
TSTG
Storage Temperature
HBM
ESD Susceptibility (Note 3)
250
mW
o
C /W
-40 to 150
o
-55 to 150
o
C
C
2
kV
VALUE
UNIT
RECOMMENDED OPERATING RANGE
SYMBOL
VIN
ITEMS
VDD Supply Voltage
TOPT
0 ~ 30
Operating Temperature
-40 to +85
V
o
C
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended
Operating Range indicates conditions for which the device is functional, but do not guarantee specific performance
limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Range. Specifications are
not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device
performance.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA,
and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA)/ θJA or the
number given in Absolute Maximum Ratings, whichever is lower.
Note 3:
Human body model, 100pF discharged through a 1.5kΩ resistor.
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
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PT4211
30V 350mA Step-down HB LED Driver
ELECTRICAL CHARACTERISTICS (Note 4, 5)
The following specifications apply for V IN=12V, TA=25 oC, unless specified otherwise.
Symbol
Parameter
Test condition
VIN
VIN supply voltage
FSW
Maximum operating frequency
VCSN
Current sense Reference voltage
VCSN_hys
Current sense Hysteretic voltage
ICSN
CSN pin bias current
IOFF
Min
Typ
5
VIN- VCSN
194
200
Max
Unit
30
V
1
MHz
206
mV
±15
%
VIN-VCSN=50mV
8
µA
Off state operating current
VDIM 230mV, the output of CS
reference remain powered during shutdown to provide
comparator switches low and the switch turns off. The
the reference for the shutdown circuit. Quiescent supply
current flowing on the RS decreases at another rate.
current during shutdown is nominally 95uA and switch
When (VIN-VCSN) < 170mV, the switch turns on again
leakage is below 5uA.
and the mean current on the LED is determined by
I OUT
0.17 0.23
0.2 / Rs .
2 Rs
Additionally, to ensure the reliability, the PT4211 is
built with a thermal shutdown (TSD) protection. The
TSD protests the IC from over temperature, when
The high-side current-sensing scheme and on-board
junction temperature more than 135℃ the output
current-setting circuitry minimize the number of
current begins to decrease until to zero at 150℃.
TYPICAL PERFORMANCE CHARACTERISTICS
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
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Page5
PT4211
30V 350mA Step-down HB LED Driver
Efficiency vs. input voltage L=47uH，ILED=350mA
100.0%
DIM pin voltage vs. VIN DIM floating
Efficiency vs. Vin L=47uH ILED =350mA
Vdim vs Vin DIM Floating
5.00
Vdim
95.0%
4.95
90.0%
4.90
Vdim(V)
Eff(%)
85.0%
80.0%
75.0%
4.85
4.80
70.0%
4.75
7
31
.0
29
.0
27
.0
25
.0
23
.0
21
.0
19
.0
17
.0
4.70
15
.0
9.
0
11
.0
7.
0
60.0%
13
.0
1LED
2LEDs
3LEDs
65.0%
9
11
13
15
17
19
21
23
25
27
29
31
Vin(V)
Vin(V)
VCS vs. Temperature Vin=12V，L=47uH
Vdim vs. Temp Vin=12V
4.950
4.940
4.930
4.920
4.910
4.900
4.890
4.880
4.870
4.860
4.850
4.840
4.830
4.820
4.810
4.800
Vcs vs. Temp Vin=12V L=47uH
220.0
Vdim
Vcs
200.0
180.0
160.0
140.0
Vcs (mV)
Vdim(V)
DIM pin voltage vs. temperature Vin=12V
120.0
100.0
80.0
60.0
40.0
20.0
0.0
-40
-20
0
20
40
60
Temp(℃)
80
100
120
-40
0
Rsw vs. temperature Vin=12V/24V
120 124 128 132 136 140 144 148
Temp (C)
Rsw vs. Vin
1.1
Vin=12V
Vin=24V
Rsw
1
1.100
1.000
0.900
0.800
0.9
0.8
Rsw(Ω )
Rsw(Ω )
80
Rsw vs. VIN
Rsw vs Temp
1.400
1.300
1.200
40
0.700
0.600
0.500
0.400
0.300
0.7
0.6
0.5
0.200
0.100
0.000
0.4
0.3
-40
-20
0
20
40
60
80
100
120
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
12
18
24
30
Vin(V)
Temp(℃)
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PT4211
30V 350mA Step-down HB LED Driver
Shut down current vs. VIN. VDIM=0
Iout vs. PWM duty cycle. Vin=12V, L=47uH
IOFF (mA) vs. Vin
IOFF (mA)
0.160
350
0.140
300
0.120
250
I LED(mA)
Ioff (mA)
I LED vs DIM L=47uH LED=1 Rcs=0.57ohm
400
0.180
0.100
0.080
Fdim=100Hz
Fdim=20kHz
200
z
150
0.060
100
0.040
50
0.020
0
0.000
1
3
5
7
9
5
11 13 15 17 19 21 23 25 27 29
15
Vin (V)
Iout vs. VIN.
L=47uH, Rcs=0.57 ohm
1LED
2LEDs
3LEDs
370
367
361
Duty(%)
ILED (mA)
364
358
355
352
349
346
343
340
7
9
11
13
15
17
19 21
Vin(V)
23
25
27
29
9
11 13 15 17 19 21 23 25 27
Vin(V)
95
29 31
I LED vs Vin L=68uH Rcs=0.57ohm
362
1LED
2LEDs
3LEDs
360
358
550
356
500
354
450
I LED(mA)
Frequency(kHz)
85
输出电流随 VIN 变化 L=68uH，Rcs=0.57 ohm
Frequency vs Vin L=47uH Rcs=0.57ohm
600
75
1LED
2LEDs
3LEDs
7
31
1LED
2LEDs
3LEDs
650
45
55
65
Duty(%)
Duty vs Vin L=47uH Rcs=0.57ohm
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
工作频率随 VIN 变化 L=47uH，Rcs=0.57 ohm
700
35
Duty cycle vs. VIN L=47uH, Rcs=0.57 ohm
I LED vs Vin L=47uH Rcs=0.57ohm
373
25
400
350
352
350
300
348
250
346
200
344
150
342
340
100
7
9
11
13
15
17
19
21
23
25
27
29
31
7
Vin(V)
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PT4211_DS Rev EN_1.1,
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9
11 13 15 17 19 21 23 25 27
Vin(V)
29 31
Page7
PT4211
30V 350mA Step-down HB LED Driver
L=68uH, Rcs=0.57 ohm
Frequency vs. VIN. L=68uH, Rcs=0.57ohm
Duty vs Vin L=68uH Rcs=0.57ohm
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Frequency vs Vin L=68uH Rcs=0.57ohm
550
1LED
2LEDs
3LEDs
1LED
2LEDs
3LEDs
500
450
Frequency(kHz)
Duty(%)
Dyty cycle vs.VIN.
400
350
300
250
200
150
100
50
0
7
9
11
13 15
17 19 21
Vin(V)
23 25
27
29
31
7
Iout vs. VIN. L=100uH, Rcs=0.57 ohm
9
Duty cycle vs. VIN.
9
29 31
L=100uH, Rcs=0.57 ohm
Duty vs Vin L=100uH Rcs=0.57ohm
1LED
2LEDs
3LEDs
Duty(%)
I LED(mA)
I LED vs Vin L=100uH Rcs=0.57ohm
359
357
355
353
351
349
347
345
343
341
339
337
335
7
11 13 15 17 19 21 23 25 27
Vin(V)
11 13 15 17 19 21 23 25 27 29 31
Vin(V)
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
1LED
2LEDs
3LEDs
7
9
11
13
15
17
19
21
23
25
27
29
31
Vin(V)
Frequency vs. VIN. L=100uH, Rcs=0.57ohm
Frequency vs Vin L=100uH Rcs=0.57ohm
500
1LED
2LEDs
3LEDs
450
Frequency (kHz)
400
350
300
250
200
150
100
50
0
7
9
11
13 15
17 19 21
Vin(V)
23 25
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
27 29
31
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PT4211
30V 350mA Step-down HB LED Driver
Dimming waveform Vin=24V，Fdim=100Hz，Duty=1%
Dimming waveform Vin=24V，Fdim=100Hz，Duty=99%
L=47uH，Rcs=0.57Ohm
L=47uH，Rcs=0.57Ohm
CH1：Iout
CH2 ：DIM pin voltage
CH1：Iout
CH2：DIM pin voltage
Dimming waveform. Vin=24V，Fdim=20KHz，Duty=10%
Dimming waveform. Vin=24V，Fdim=20KHz，Duty=90%
L=47uH，Rcs=0.57Ohm
L=47uH，Rcs=0.57Ohm
CH1 ：Iout CH2 ：DIM pin voltage
CH1 ：Iout
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CH2 ：DIM pin voltage
Page9
PT4211
30V 350mA 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:
I OUT 0.2 / Rs
( Rs 0.17)
This equation is valid when DIM pin is logic high.
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:
I OUT
0.2 D
(0 D 100%)
Rs
RS
VIN
0.58Ω
LED
1W
L
68uH
D
VIN
CSN
DIM
PT4211
SW
GND
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 PWM signal
cycle 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 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 PT4211 is
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
depending on the operating frequency. To achieve the
best dimming linearity, the dimming frequency is
recommended to limited less than 1% of operating
frequency.
Shutdown mode
Taking the DIM pin to a voltage below 0.4V will turn
off the output and the supply current will fall to a low
standby level of 95μA nominal.
Inherent open-circuit LED protection
If the connection to the LED(s) is open-circuited, the
coil is isolated from the SW pin of the chip, so the
device and LED will not be damaged. When the LED(s)
load is connected the device will enter normal
operation.
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
4.7uF is acceptable if the DC input source is close to
the device, but higher values will improve performance
at lower input voltages, especially when the source
impedance is high. For the rectified AC input, the
capacitor should be higher than 100uF and the tantalum
capacitor is recommended. 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.
A
suitable
Murata
capacitor
would
be
GRM42-2X7R475K-50.
The following web sites are useful when finding
alternatives:
www.murata.com
www.t-yuden.com
www.avxcorp.com
Inductor selection
Recommended inductor values for the PT4211 are in
the range 47uH to 100uH.
Higher values of inductance are recommended at lower
output current in order to minimize errors due to
switching delays, which result in increased ripple and
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PT4211
30V 350mA Step-down HB LED Driver
lower efficiency. Higher values of inductance also
result in a smaller change in output current over the
supply voltage range. (See graphs). The inductor should
be mounted as close to the device as possible with low
resistance connections to the SW 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.
Following table gives the guideline on inductor
selection:
Saturation
1LED
Vin
2LEDs
5V-10V
47uH
68uH
10V-20V
68uH
68uH
100uH
68uH
20V-30V
3LEDs
current
1.3-1.5
47uH
times of
load
47uH
current
Suitable coils for use with the PT4211 are listed in the
table below:
Part
L
DCR
ISAT
No.
(uH)
(Ω)
(A)
MSS1038-473
47
0.128
2
MSS1038-683
68
0.213
1.6 www.coilcraft.co
MSS1038-104
100
0.304
1.3 m
Manufacturer
CoilCraft
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.
The following equations can be used as a guide.
SW Switch 'On' time
TON
VIN VLED
L I
I avg ( Rs rL Rsw )
VLED
VLED is the total LED forward voltage (V)
RSW is the switch resistance (Ω ) {=1Ω nominal}
VD is the diode forward voltage at the required load
current (V)
Diode selection
For maximum efficiency and performance, the rectifier
(D) 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 diodes,
due to a combination of lower forward voltage and
reduced recovery time.
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 and if close
to the load may create a thermal runaway condition.
The higher forward voltage and overshoot due to
reverse recovery time in silicon diodes will increase the
peak voltage on the SW output. If a silicon diode is
used, care should be taken to ensure that the total
voltage appearing on the SW pin including supply
ripple, does not exceed the specified maximum value.
The following web sites are useful when finding
alternatives: www.onsemi.com
Reducing output ripple
Peak to peak ripple current in the LED(s) can be
reduced, if required, by shunting a capacitor CLED
across the LED(s) as shown below:
RS
VIN
SW Switch 'Off' time
TOFF
VIN is the supply voltage (V)
0.58Ω
LED
1W
L I
VD I avg ( Rs rL)
L
68uH
D
Where:
L is the coil inductance (H)
VIN
CSN
DIM
PT4211
rL is the coil resistance (Ω )
RS is the current sense resistance (Ω )
SW
GND
Iavg is the required LED current (A)
Δ I is the coil peak-peak ripple current (A) {Internally
set to 0.3 x Iavg}
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Page11
PT4211
30V 350mA Step-down HB LED Driver
A value of 1uF will reduce the supply 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 and reduce
the frequency of dimming, by reducing the rate of rise
Operation at low supply voltage
With the supply voltage below the output voltage, 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.
Thermal considerations
When operating the device at high ambient
temperatures, or when driving maximum load, care
must be taken to avoid exceeding the package power
dissipation limits. Note that the device power
dissipation will most often be a maximum at minimum
supply voltage. It will also increase if the efficiency of
the circuit is low. This may result from the use of
unsuitable coils, or excessive parasitic output
capacitance on the switch output.
Thermal shutdown protection
To ensure the reliability, the PT4211 is built with a soft
over temperature protection function. When junction
temperature excess 135℃ the output current begin to
decrease until to zero at 150℃. The soft over
temperature function protects the IC and avoid the
flicker when operation at high temperature.
Layout considerations
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
of LED voltage.
By adding this capacitor the current waveform through
the LED(s) changes from a triangular ramp to a more
sinusoidal version without altering the mean current
value.
Careful PCB layout is critical to achieve low switching
losses and stable operation. Use a multilayer board
whenever possible for better noise immunity. Minimize
ground noise by connecting high-current ground returns,
the input bypass-capacitor ground lead, and the
output-filter ground lead to a single point (star ground
configuration).
SW pin
The SW 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 CSN 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
because of track resistance.
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PT4211
30V 350mA Step-down HB LED Driver
TYPICAL APPLICATION CIRCUIT
RS
VIN
0.58Ω
DC5-30V
D
LED
1W
L=100uH
5
AC1218V
CIN
4
100uF
VIN
CSN
PT4211
SW
GND
1
2
DIM
3
Fig1 ：1W application
RS
VIN
0.58Ω
DC5-30V
D
LED
1W
L=100uH
5
AC1218V
CIN
4
100uF
VIN
CSN
PT4211
SW
GND
1
2
DIM
3
Fig 2： 3W application
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PT4211
30V 350mA Step-down HB LED Driver
PACKAGE INFORMATION
SOT23-5
SYMBOL
A
A1
A2
A3
b
b1
c
c1
D
E
E1
e
e1
L
L1
L2
R
R1
θ
θ1
θ2
China Resources Powtech (Shanghai) Limited
PT4211_DS Rev EN_1.1,
MIN
0
1.00
0.60
0.36
0.36
0.14
0.14
2.826
2.60
1.526
0.35
0.10
0.10
0°
3°
6°
MILLIMETERS
TYP
1.10
0.65
0.38
0.15
2.926
2.80
1.626
0.95BSC
1.90BSC
0.45
0.59REF
0.25BSC
5°
8°
WWW.CRPOWTECH.COM
MAX
1.25
0.15
1.20
0.70
0.50
0.45
0.20
0.16
3.026
3.00
1.726
0.60
0.25
8°
7°
10°
Page14
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