GENERAL DESCRIPTION
The PT4110 is a high efficiency step-up DC/DC converter designed for driving multiple strings of up to eight ries-connected white LED from a single cell Lithium Ion battery. It regulates the output current, ideal for driving light emitting diodes (LED) who light intensity is proportional to the current passing through them. The external ballast resistor ts the LED current ranging from 5mA to 20mA, which can be easily adjusted using either a DC voltage or a pul width modulated (PWM) signal alternatively. Its low 300mV feedback voltage reduces power loss and improves efficiency.
The PT4110 has multiple features to protect itlf from fault conditions including built-in open load protection, cycle-by-cycle current limit, over temperature shutdown, input under voltage control and integrated soft-start.
The PT4110 is available in SOT-89-5 and SOP-8 packages.
FEATURES
z 2.7V to 5.5V Input V oltage Range z 35V Maximum Step-Up V oltage z <1µA Shutdown Mode
z 1.2MHz Fixed Frequency Operation z Cycle-By-Cycle Current Limit z Open Load Protection z Under V oltage Lockout z Integrated Soft-Start z Thermal Shutdown
z Frequency Jittering for better EMI performance z SOT89-5 or SOP8 package z
RoHS compliant
APPLICATIONS
z White LED Power Suppliers z Flat Screen LCD Bias Suppliers z Portable Media Players z GPSs
z
General middle-sized LCD backlight
ORDERING INFORMATION
PACKAGE
TEMPERATURE
RANGE
ORDERING PART
产学研用一体化NUMBER
TRANSPORT MEDIA MARKING SOT89-5, Pb free -40℃ to 85℃ PT4110E89E Tape and Reel 1000 unis PT4110 xxxxxX SOP8, Pb free
-40℃ to 85℃ PT4110ESOH
Tape and Reel 2500 units
PT4110 xxxxxX
Note:
TYPICAL APPLICATION CIRCUIT
A sm bly Factory Code
Lot N um ber
PIN ASSIGNMENT
PIN DESCRIPTIONS
PIN NUMBER SOT89-5
SOP8 PIN NAME PIN DESCRIPTION
1 1 IN Input Supply Pin. Must be locally bypasd.
2
2
GND
Signal and power ground. Connect directly to ground plane.
3 3 EN
Enable input pin with 500kohmn pull-down resister. The voltage applied to this pin should be either less than 0.4V or more than 1.5V to turn off and on the device
respectively. The EN pin can also be ud for PWM dimming control. The PWM square wave applied to this pin must be within the range from 100Hz to 100kHz. 4 6 FB
Feedback Input. The PT4110 regulates the voltage across the current n resistor between FB and GND. Connect a current n resistor from the bottom of the LED
string to GND. Connect the bottom of the LED string to FB. The regulation voltage is 300mV.
5 8 SW Switch Output. SW is the drain of the internal N-Channel MOSFET switch. Connect
the power inductor between SW and the input source, and connect the output
rectifier between SW and the output to form the step-up converter.
EP
Expod PAD Only for SOT89-5. Internally connected to GND. Mount on board for lower thermal
resistance.
2, 4, 5
NC
Not connection
ABSOLUTE MAXIMUM RATINGS (note1)
SYMBOL
ITEMS
V ALUE UNIT V IN Supply V oltage -0.3~7 V SW Drain of the internal power switch -0.3~40 V All Other Pins
-
0.3~7 V θJA-SOT89-5 Thermal resistance for SOT89-5 65 ℃/W θJA-SOP-8 Thermal resistance for SOP-8 105
℃/W
P DMAX Power Dissipation SOT89-5(Note 2) 1 W T J Operation Junction Temperature Range
-40 to 125 o C T STG Storage Temperature
-55 to 150
o
C
ESD Susceptibility (Note 3)乌鸦医生
2
kV
RECOMMENDED OPERATING RANGE
SYMBOL ITEMS
V ALUE UNIT V IN V DD Supply V oltage 2.7 ~ 5.5 V
T OPT
Operating Temperature
-40 to +85
o
C
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. R
ecommended
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 T JMAX , θJA , and the ambient temperature T A . The maximum allowable power dissipation is P DMAX = (T JMAX - T A )/ θJA or the number given in Absolute Maximum Ratings, whichever is lower.
Note 3: Human body model, 100pF discharged through a 1.5k Ω resistor.
ELECTRICAL CHARACTERISTICS (Note 4, 5)
V IN =V EN =3.6V , TA=25℃ unless specified otherwi SYMBOL ITEMS
CONDITIONS Min.
Typ.
Max.
UNIT
植树节手抄报内容V IN Input Voltage
2.7 5.5 V V UVLO Under voltage lock out
V IN rising 2.3 V V UVLO, HYS UVLO hysterisis
V IN falling
100
mV
Feedback
V FB FB Pin Voltage 280 300 320 mV I BIAS FB Pin Input Bias Current
0.05
1
µA
Operating Current
I OFF Operating Current （Shutdown ） V SW-ON =0V
0.1
1
µA
I OP Operating Current （Active ） 3 5 mA
F SW Switching Frequency
1.0 1.2 1.5 MHz
D MAX Maximum Duty Cycle
V FB =0V 90 95 %
Chip Enable
V EN_H EN Minimum High Level 1.5 V V EN_L EN Maximum Low Level
0.4
V
Output Switch
R ON SW On Resistance V IN =
绿豆粉条5V 0.4 Ω I LIMIT
SW Current Limit
1.2
1.5
A
I LEAK SW Leakage Current V sw ＝5V
马后炮0.01 1 µA
分班Open Circuit Protection
V OV Open Circuit Shutdown Threshold
V IN = 5V
35
V
Soft Start
t SST Soft Start Time V IN Power On 0.8 ms Note 4: Typical parameters are measured at 25˚C an
d reprent the parametric norm. Note 5: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
SIMPLIFIED BLOCK DIAGRAM
OPERATION DESCRIPTION
The PT4110 us a constant frequency, peak current mode boost regulator architecture to regulate the ries string of white LED. The operation of the PT4110 can be understood by referring to the block diagram. At the start of each oscillator cycle the power MOSFET, M1, is turned on through the control circuitry. To prevent sub-harmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the output of the current n amplifier and the result is fed into the positive input of the PWM comparator. When this voltage equals the output voltage of the error amplifier the power MOSFET is turned off. The voltage at the output of the error amplifier is an amplified version of the difference between the 300mV reference voltage and the feedback voltage. In this way the peak current level keeps the output in regulation. If the feedback voltage starts to drop, the output of the error amplifier
increas. This results in more current flowing through the power MOSFET, thus increasing the power delivered to the output.
The PT4110 can be ud to drive multiple strings of white LED as shown in figure “typical application”. The brightness of each LED in such kind of connection will almost be the same provided that the number of ries-connected LED in each string is equal and each string is terminated with a well-matched ballast resistor. Otherwi the differential current among strings will b
e huge enough to cau damage to LED permanently. To protect the step-up converter when the load is open, or the output voltage becomes excessive for any reason, the PT4110 features a dedicated open LED protection. When the output is in open circuit, and the input voltage exceeds 4.5V , the step-up converter switches off immediately and won’t be enabled until restart chip.
TYPICAL PERFORMANCE CHARACTERISTICS
0.72
0.740.760.780.800.820.84
0.86
0.880.90E f f i c i e n c y
Iout (mA)
I o u t (m A )
Duty Cycle
APPLICATION INFORMATION
Setting the LED current
The LED current is controlled by the feedback resistor. The feedback reference is 300mV. The LED current is 300mV/R FB. In order to have accuracy LED current, precision resistor is preferred. (1% is recommended). Selecting the inductor
Choo an inductor that does not saturate under the worst-ca load transient and startup conditions. A good rule for determining the inductance is to allow the peak-to-peak ripple current to be approximately 30% to 50% of the maximum input current. Make sure that the peak inductor current is below 1.2A to prevent loss of regulation due to the current limit. For most of the applications of the PT4110, it is recommended to u an inductor of 10uH.
Selecting the Input Capacitor
An input capacitor is required to supply the AC ripple current to the inductor, while limiting noi at the input source. A low ESR capacitor is required to keep the noi at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice.
U an input capacitor value greater than 22μF. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating. U a capacitor with RMS current rating greater than the inductor ripple current.
Selecting the Output Capacitor
The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple to a minimum. The characteristic of the output capacitor also affects the stability of the regulation control system. 2.2uF ceramic, tantalum, or low ESR electrolytic capacitors are recommended.香港公司查册
Selecting the Diode
The output rectifier diode supplies current to the inductor when the internal MOSFET is off. To reduce loss due to diode forward voltage and recovery time, u a Schottky diode. Choo a diode who maximum rever voltage rating is greater than the maximum output voltage. The rated average forward current needs to be equal to or greater than the load current.
Open Circuit Protection
when the input voltage exceeds 4.5V, the open load protection will shut off the PT4110 if the output is in open circuit. In some cas an LED may fail, which will result in the feedback voltage always being zero. The PT4110 will then switch at its maximum duty cycle boosting the output voltage highe
r and higher. The PT4110 detects the voltage of SW pin. The output of PT4110 is equal high level of SW pin subtracting the forward voltage of the Schottky diode. If the SW pin exceeds 35V for veral periods, the PT4110 will shut down. The part will not switch again until the power is recycled.
Dimming Control
There are two different types of dimming control circuits:
1. Using a DC Voltage
For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown as below. As the DC voltage increas, the voltage drop on R2 increas and the voltage drop on R1 decreas. Thus, the LED current decreas. The lection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current.
2. Using a PWM Signal to EN Pin
With the PWM signal applied to the EN pin, the reference of PT4110 is changed with the duty cycle of the PWM signal. The LEDs operate at either zero or full current. The average LED current increas proportionally with the duty cycle of the PWM signal.
乒乓球海报A 0% duty cycle will turn off the PT4110 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal should be higher than 20 kHz to avoid the audio noi.
