AX3301
PWM Step-Down Controller GENERAL DESCRIPTION
The AX3301 integrates Pul-Width-Modulation (PWM) control circuit into a single chip. The devi include a reference voltage source, oscillation circuit, error amplifier and etc.
AX3301 provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to very the duty ratio linearly form 0 up to 100%. This controller also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. An enable function, an over current protect function and short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced. Also, an internal compensation block is built in to minimum external component count.
With the addition of an external P-channel Power MOS, a coil, capacitors, and a diode connected externally, the components can function as step-down switching regulators. They rve as ideal power supply units for portable devices when coupled with the SOP-8L & MSOP-8L mini-package, prov
iding such outstanding features as low current consumption. Since this converter can accommodate an input voltage up to 24V, it is also suitable for the operation via an AC adapter.
FEATURES
-Input voltage 3.6V to 24V
-Output voltage 0.8V to Vcc
-Duty ratio 0% to 100% PWM control
-Oscillation frequency 330 KHz typ.
-Soft-start (SS), Current Limit (CL), Enable function.
-Thermal Shutdown function.
-Short Circuit Protect (SCP).
-External SW P-channel MOS.
-MSOP-8L & SOP-8L Pb-Free package.
1/11
Block Diagram
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GATE
Vcc
FB
PIN ASSIGNMET
The packages of AX3301 are MSOP-8L & SOP-8L; the pin assignment is given by:
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Description
EN Shutdown Control Input. H normal operation(Step-down)
L Shutdown mode
OCSET
Add an external resistor to t max
switch output current.
小腹痛男性什么原因V CC IC power supply pin
GATE
Gate drive for external P-channel
MOSFET.
( Top View )
LX EN FB Vss Vcc
GATE
NC Oct MSOP - 8L & SOP - 8L
LX LX is the current n input. V SS GND pin
FB
Feedback pin
Absolute Maximum Ratings (at Ta=25 )
Characteristics Symbol Rating Unit VCC Pin Voltage V CC V SS - 0.3 to V SS + 26 V Feedback Pin Voltage V FB V SS - 0.3 to V CC V
ON/OFF Pin Voltage V EN V SS - 0.3 to V CC + 0.3 V Switch Pin Voltage V SW V SS - 0.3 to V CC + 0.3 V Power Dissipation PD Internally limited mW
Storage Temperature Range T ST
-40 to +150 Operating Temperature Range T OP -20 to +125
Operating Supply Voltage
V OP +3.6 to +24
V
Thermal Resistance from Junction to ca
θJC SOP8=40, MSOP8=45 /W Thermal Resistance from Junction to ambient
θJA
SOP8=120, MSOP8=200
/W
Note : JA is measured with the PCB copper area of approximately 1 in 2(Multi-layer).
Electrical Characteristics (V CC = 12V, Ta=25°C, unless otherwi specified)
Characteristics Symbol Conditions Min Typ Max Units
西安植物园Feedback Voltage V FB I OUT =0.1A 0.784 0.800 0.816 V
Quiescent Current I CCQ V FB =1.2V force driver off 3 5 mA Feedback Bias Current I FB I OUT =
0.1A - 0.1 0.5 uAaslongasyouloveme
Shutdown Supply Current I SD V EN =0V
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2
10
uA
OCSET pin bias current I OCSET
95 110 125 uA
Line Regulation V OUT /V OUT V CC = 5V~24V, I OUT =
0.2A - 0.6 1.2 % Load Regulation V OUT /V OUT I OUT = 0.1 to 5A -
0.3
0.5
%
Oscillation Frequency F OSC SW pin 260 330 400 KHz V SH High (regulator ON) 2.0 - - EN Pin Logic input threshold voltage V SL Low (regulator OFF) - - 0.8
V
I SH V EN =2.5V (ON) - 20 - uA EN Pin Input Current I SL V EN =0.3V (OFF)
- -10 - uA Soft-Start Time T SS
0.3 4 8 ms
LX Ri Time T LXR C LX =
1000pF 45
LX Fall Time T LXF C LX =
1000pF 45 nS
I OUT = 2A - 92 -
Efficiency
EFFI V OUT = 5V I OUT = 3A
- 91 - %
Thermal shutdown Temp
北京旅游必去景点TSD
125
Application Circuit
A.Typical circuit
B.Standby current (Iout=0A) < 4mA
Function Descriptions
PWM Control
The AX3301 integrates Pul-Width-Modulation (PWM) control circuit into a single chip.
The pul width varies in a range from 0 to 100%, according to the load current. The ripple voltage produced by the switching can easily be removed through a filter becau the
switching frequency remains constant. Therefore, the controllers provide a low-ripple power over broad ranges of input voltage and load current.
RDS (ON) Current Limiting
The current limit threshold is tting by the external resistor (R3) connecting from V CC supply to OCSET pin. The internal 110uA sink current crossing the resistor ts the voltage at pin of OCSET. When the PWM voltage is less than the voltage at OCSET, an over-current condition is triggered. Plea refer to the formula for tting the current limit value
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R I I DS(ON)
OCSET SW(MAX)
075.0R3+×=
(Normally, The I SW(MAX) tting more than I OUT 0.5~1.0A ).
Example:
I SW = (110uA * 1.8k + 0.075)/ 50m Ω (AP9435GM SPEC) = 5.5A
Setting the Output Voltage
Application circuit item shows the basic application circuit with AX3301 adjustable output version. The external resistor ts the output voltage according to the following equation:
⎟⎠
⎞⎜⎝⎛
+×=2118.0R R V V OUT
Table 1 Resistor lect for output voltage tting
V OUT R2 R1 1.3K 6.8K 5V 5.6K 30K 1.5K 4.7K 3.3V 5.6K 18K 2.2K 4.7K 2.5V
5.6K 12K
1.8V 1.2K 1.5K 1.5V
2.2K 2.0K
Inductor Selection
For most designs, Low inductance values are physically smaller but require faster
switching, which results in some efficiency loss. The inductor value can be derived from the following equation:
()f
I V V V V L
LX
L IN OUT IN OUT ××−×=∆
Where is inductor Ripple Current. Large value inductors lower ripple current and small
value inductors result in high ripple currents. Choo inductor ripple current approximately 15% of the maximum input current 3A, ∆I L=0.45A.
Table 2 Inductor lect for output voltage tting (AX3301 at V CC=12V)
5V(5A) V OUT 2.5V 3.3V 5V 3.3V(5A)
L1 Value 15uH 18uH 22uH 12uH 15uH 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 (3A+0.3A).
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noi from the device. The input capacitor impedance at the switching frequency shall be less
than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be ud.
The capacitor voltage rating should be at least 1.5 times greater than the input voltage, and often much higher voltage ratings are needed to satisfy.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. A low ESR capacitor sized for maximum RMS current must be ud. the low
ESR requirements needed for low output ripple voltage.
The capacitor voltage rating should be at least 1.5 times greater than the input voltage, and often much higher voltage ratings are needed to satisfy.
Layout Guidance
When laying out the PC board, the following suggestions should be taken to ensure proper operation of the AX3301. The items are also illustrated graphically in below.
1. The power traces, including the PMOS Drain & Source trace, the Schottky and the C2 trace should be kept short, direct and wide to allow large current flow.
2. Keep the switching node, away from the nsitive FB node.
3. Connect ground side of the C2 & D1 as cloly as possible.
4. Connect PMOS Source and R3 as cloly as possible.
5. Do not trace signal line under inductor.
