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* The output voltage is t by R2 and R3: V OUT = 1.21V • [1 + (R2/R3)].
* R T: R T is optional. The resistor range is from 130KΩto 1.5 MΩ. FT021G can work when keeping RT pin floating. The default frequency is 130KHZ.
如何打拼音* I LIM: FT021G can work when keeping ILIM pin floating, with 2.7A limit current in this situation.
P i n A s s i g n m e n t a n d D e s c r i p t i o n
A b s o l u t e M a x i m u m R a t i n g s(N o t e1)
Input Supply Voltage ....................................................................................................-0.3V ～ 35V FB, ILIM, . -0.3V ～ 6V SW Voltage ........................................................................................................-0.3V ～(VIN + 1V) Operating Temperature Range (Note 2).........................................................-40℃～ +85℃ Storage -65℃～ +150℃ Junction Temperature Range.. (150)
Lead Temperature (Soldering, 10 c.) (265)
Note 1: Stress beyond tho listed Absolute Maximum Ratings may cau permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.
Note 2: The FT021G is guaranteed to meet performance specifications from 0℃ to 70℃. Specifications over the –40℃to 85℃ operating temperature range are assured by design, characterization and correlation with statistical process controls.
PIN NAME DESCRIPTION
1 FB Feedback
2 RT Frequency
Setting
3 ILIM Current
Limit
4 VIN Input Supply Voltage
5, 6 SW Switch Node
7, 8 GND Ground
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E l e c t r i c a l C h a r a c t e r i s t i c s
Operating Conditions: T A=25, V
℃IN=12V, R2=470k, R3=150k, unless otherwi specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V IN Operating Voltage Range 8 30 V
I Q Quiescent
Current I LOAD
=0A 10
15
20
mA
I SHDN Shutdown
Current 110 150 μA V UVLO Input UVLO Threshold 4.25 4.5 V
ΔV UVLO UVLO
Hysteresis 50 100
mV V FB Regulated
Voltage 1.188 1.21 1.236 V
I FB Feedback Pin Input Current0.05 μA
f OSC Oscillator Frequency Range Float RT Pin 130 kHz
f OSC_MAX Maximum Oscillator
Frequency
500 kHz
DC Max Duty Cycle 100 % I LIM_def Default Limit Current Float ILIM Pin 2.7 A
I LIM-TH Current Limit Sen Pin
Source Current 7 8.5 10 μA八王之乱是哪八王
R PFET R DS(ON) of P-Channel FET 65 mΩR NFET R DS(ON) of N-Channel FET 30 mΩT SD Thermal Shutdown Temperature
Rising 145 ℃
ΔT SD Thermal Shutdown
Hysteresis 30
℃
P i n F u n c t i o n s
FB (Pin 1): Feedback Pin. Receive the feedback voltage from an external resistive divider across the output. In the adjustable version, the output voltage is fixed. The Output voltage is t by R2 and R3:
V OUT = 1.21V • [1 + (R2/R3)].
RT (Pin 2): The internal oscillator is t with a single resistor between this pin and the GND pin.
ILIM (Pin 3): Monitors current through the high-side switch and triggers current limit operation if the inductor valley current exceeds a ur defined value that is t by R LIM and the Sen current sourced out of this pin during operation.
VIN (Pin 4): Main Supply Pin. The FT021G operates from 8V to 30V unregulated input. It must be cloly decoupled to GND, with a 47μF or greater ceramic capacitor to prevent large voltage spikes from appearing at the input.
SW (Pin 5, 6): Switch Node Connection to Inductor.
GND (Pin 7, 8): Ground Pin.不相信眼泪
B l o c k D i a g r a m
A p p l i c a t i o n I n f o r m a t i o n
The FT021G operates by a constant frequency, current mode architecture. The output voltage is t by an external divider returned to the FB pin. An error amplifier compares the divided output voltage with a reference voltage of 1.21V and adjusts the peak inductor current accordingly.
During normal operation, the internal P-channel MOSFET is turned on each cycle when the oscillator ts the RS latch, and turned off when the current comparator, rets the RS latch.While the P-channel MOSFET is off, the N-channel MOSFET is turned on until either the inductor current starts t
o rever, as indicated by the current reversal comparator or the beginning of the next clock cycle.
Thermal Protection
The total power dissipation in FT021G is limited by a thermal protection circuit. When the device temperature ris to approximately 145℃, this circuit turns off the output, allowing the IC to cool.The thermal protection circuit can protect the device from being damaged by overheating in the event of fault conditions.Continuously running the FT021G into thermal shutdown degrades device reliability.
Current Limit
Current limit detection occurs during the on-time by monitoring the current through the high-side P-MOSFET. The current limit value is defined by R LIM. If during the on-time the current in the high-side P-MOSFET exceeds the ur defined current limit value, the next on-time cycle is immediately terminated.Current nsing is achieved by comparing the voltage across the high-side FET with the voltage across the current limit t resistor R LIM. The current limit value ris when the t resistor R LIM ris.
后羿神弓Oscillator Frequency
The FT021G oscillator frequency is t by a single external resistor connected between the RT pin and the GND pin. The resistor should be located very clo to the device and connected directly to the pins of the IC (RT and GND). An internal amplifier holds the RT pin at a fixed voltage typically 0.6V. The oscillator frequency ris when the resistor R T falls. To determine the timing resistance for a given switching frequency, u the equation below:
R T(kΩ)= 4800000/ (200*f OSC(kHz)-24000)
Setting Output Voltage
The output voltage is t with a resistor divider from the output node to the FB pin. It is recommended to u divider resistors with 1% tolerance or better.To improve efficiency at very light loads consider using larger value resistors. If the values are too high the regulator is more susceptible to noi and voltage errors from the FB input current are noticeable. For most applications, a resistor in the 10kΩ to 1MΩrange is suggested for R3. R2 is then given by:
R2 = R3 • [(V OUT / V REF) – 1]
where V REF is 1.21V.
Output Cable Resistance Compensation
To compensate for resistive voltage drop across the charger's output cable, the FT021G integrates a
simple, ur-programmable cable voltage drop compensation using the impedance at the FB pin. Choo the proper feedback resistance values for cable compensation. The delta VOUT voltage ris when the feedback resistance R3 value ris. The delta VOUT voltage ris when the feedback resistance R3 value ris. Inductor Selection
For most applications, the value of the inductor will fall in the range of 4.7μH to 47μH. Its value is chon bad on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increas the ripple current as shown in equation. A reasonable starting point for tting ripple current is I △L =1.12A (40% of 2.8A).
The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 3.92A rated inductor should be enough for most applications (2.8A + 1.12A). For better efficiency, choo a low DC-resistance inductor.
Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or perm alloy materials are small and don’t radiate much energy, but generally cost more than powdered iron core inductors with similar electrical chara
cteristics. The choice of which style inductor to u often depends more on the price vs. size requirements and any radiated field/EMI requirements than on what the FT021G requires to operate. Output and Input Capacitor Selection
In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V OUT /V IN . To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be ud. The maximum RMS capacitor current is given by:
秋思是什么意思This formula has a maximum at V IN = 2V OUT , where I RMS = I OUT /2. This simple worst-ca condition is commonly ud for design becau even significant deviations do not offer much relief. Note that the capacitor manufacturer’s ripple current ratings are often bad on 2000 hours of life. This makes it advisable to further derate the capacitor, or choo a capacitor rated at a higher temperature than required. Always consult the manufacturer if there is any question.
The lection of C OUT is driven by the required effective ries resistance (ESR).Typically, once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the I RIPPLE(P-P) requirement. The output ripple ΔV OUT is determined by:
Where f = operating frequency, C OUT = output capacitance and ΔI L = ripple current in the inductor.
For a fixed output voltage, the output ripple is highest at maximum input voltage since ΔI L increas with input voltage.
FT021G
