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AX3513-V1.2

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1.4MHz, 1A Synchronous Step-Down

Converter

GENERAL DESCRIPTION

AX3513 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version. Supply current with no load is 250uA and drops to <1uA in shutdown. The 2.5V to 6V input voltage range makes AX3513 ideally suited for single Li-Ion, two to four AA battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. Switching frequency is internally set at 1.4MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous switch increases efficiency and decreases need of an external schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. AX3513 is available in small TSOT23-5L and DFN-6L packages. FEATURES

- 2.5V to 6V Input Voltage Range - Output Voltage from 0.6V to VIN - High Efficiency: Up to 96%

- 1.4MHz Constant Frequency Operation - Up to 1A Output Current

- Quiescent Current: 250uA (Typical) - No Schottky Diode Required

- Current Mode Operation for Excellent Line and Load Transient Response - Current limit, Enable function - Short Circuit Protect (SCP) - Build in soft start function - ≤ 1μA Shutdown Current

- TSOT23-5L and DFN-6L Pb-Free packages

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BLOCK DIAGRAM

VIN

SW GND

PIN ASSIGNMENT

The packages of AX3513 are TSOT23-5L and DFN-6L; the pin assignment is given by:

(Top View)

EN GND SW

VIN FB 12

TSOT23-5L

DFN-6L (2*2)

VIN FB SW

EN GND NC

Name

Description

EN Enable pin

H ：normal operation

L ：Shutdown

VIN Power Supply Input Pin

Switch output pin. Connect external inductor here. Minimize trace area at this pin to reduce EMI. GND Ground Pin

FB Output Feedback pin NC No Connect.

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ABSOLUTE MAXIMUM RATINGS (at T A =25°C)

Characteristics

Symbol Rating Unit VIN Pin Voltage V IN V SS - 0.3 to V SS + 6.5 V Feedback Pin Voltage V FB V SS - 0.3 to V IN + 0.3 V EN Pin Voltage V EN V SS - 0.3 to V IN + 0.3 V Switch Pin Voltage

V SW V SS - 0.3 to V IN + 0.3

Peak SW Sink and Source Current I PSW 1.4 A

Power Dissipation

PD ( T J -T A ) / θJA mW Storage Temperature Range T ST -40 to +150 °C Operating Temperature Range T OP

-40 to +85

°C

Junction Temperature

T J +125 °C

DFN-6L 25 Thermal Resistance from Junction to case TSOT23 θJC 110 °C/W

DFN-6L 120

Thermal Resistance from Junction to ambient TSOT23 θJA 250

°C/W

Note: θJA is measured with the PCB copper area of approximately 1 in 2(Multi-layer). That need connect to GND pin or exposed pad (AX3513Z2).

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ELECTRICAL CHARACTERISTICS

(V IN = V EN =3.6V, T A =25°C, unless otherwise specified)

Characteristics Symbol

Conditions

Min

Typ

Max Units

Input Voltage Range V IN 2.5 - 6 V T A = +25°C 0.588 0.600 0.612 Feedback Voltage V FB -40°C ≤T A ≤ 85°C

0.582 0.600 0.618

Feedback Bias Current I FB V FB =

0.65V - - ±30 nA Quiescent Current I CCQ V FB =1V - 250 350 uA Shutdown Supply Current I SD

V EN =0V

0.1

Switching Current Limit I LIMIT 1.2 1.4 - A

Line Regulation △V OUT /V OUT V IN = 2.5V to 5.5V

0.04 0.4 %/V Load Regulation △V OUT /V OUT I OUT = 0.01 to 1A

0.5

Oscillation Frequency F OSC SW pin 1.1 1.4 1.7 MHz R DS(ON) of P-CH MOSFET R DSON V FB = 0V, I OUT = 0.5A - 0.3 0.4 ? R DS(ON) of N-CH MOSFET R DSON (Note 1)

- 0.25 0.35 ? V ENL

- - 0.4

EN pin logic input threshold voltage

V ENH 1.5 - - V

EN Pin Input Current

I EN

- ±0.1 ±1 uA Efficiency EFFI

V IN =5V, V OUT =3.3V,

I OUT =0.5A

- 94 - % Thermal shutdown

T DS - 140 - °C Thermal

shutdown Hysteresis T SH

- 30 - °C

Note 1: Guaranteed by design.

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APPLICATION CIRCUIT

FUNCTION DESCRIPTIONS

Operation

AX3513 is a monolithic switching mode step-down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This step-down DC-DC Converter supplies minimum 1000mA output current at input voltage range from 2.5V to 5.5V.

Current Mode PWM Control

Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line transient responses and protection of the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, I COMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, I ZERO , or the beginning of the next clock cycle.

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APPLICATION INFORMATION

Setting the Output Voltage

Application circuit item shows the basic application circuit with AX3513 adjustable output version. The external resistor sets the output voltage according to the following equation:

????

+×=2116.0R R V V

OUT

Table 1 Resistor select for output voltage setting

V OUT R2 R1 1.2V 300K 300K 1.5V 300K 450K 1.8V 300K 600K 2.5V 150K 470K 3.3V 120K 540K

Inductor Selection

For most designs, the AX3513 operates with inductors of 2.2μH to 3.3μH. 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:

()

I V

V V V L OSC

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. Choose inductor ripple current approximately 20% of the maximum load current 1000mA, ΔI L =200mA.

Table 2 Inductor select for output voltage setting (V IN =3.6V)

V OUT 1.2V 1.5V 1.8V 2.5V Inductor 2.7uH 2.7uH 2.7uH 2.2uH Part Number

WE-TPC

7440430027 7440430027 7440430027 7440430022

Note: Part type MH or M (https://www.sodocs.net/doc/f212274292.html,)

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For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.7μH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50m ? to 150m ? range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m ?. 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 (1000mA+100mA).

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching noise 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 used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 4.7μF ceramic capacitor for most applications is sufficient.

Output Capacitor Selection

The output capacitor is required to be 10uF to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current.

Compensation Capacitor Selection

The compensation capacitors for increasing phase margin provide additional stability. It is required 15pF, Please refer to Demo Board Schematic to design.

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TSOT23-5L Layout Guide

connected to Inductor by wide keep sensitive components C1's ground must be as closer to IC's GND pin as possible

closer to IC's FB pin as possible

DFN-6L Layout Guide

SW should be connected to Inductor by wide and short trace,keep sensitive components away from this trace

C1 and C2's ground must be as closer to IC's GND pin as possible

closer to IC's FB pin as possible and keep the switching trace away.

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TYPICAL CHARACTERISTICS

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TYPICAL CHARACTERISTICS (CONTINUES)

Power-on Waveform

EN-ON Waveform

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TYPICAL CHARACTERISTICS (CONTINUES)

EN-ON Waveform

Load Transient

TSD to release

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PACKAGE OUTLINES

(1) TSOT23-5L

Dimensions In Millimeters Dimensions In Inches

Symbol

Min. Nom. Max. Min. Nom. Max.

A 0.75 - 1.0 0.030 - 0.039 A1 0.00 - 0.15 0.000 - 0.004 A2 0.70 0.75 0.85 0.028 0.030 0.034 b 0.35 - 0.51 0.014 - 0.020 C 0.10 - 0.25 0.004 - 0.010 D 2.80 2.90 3.00 0.110 0.114 0.118 E 2.60 2.80 3.00 0.102 0.110 0.118 E1 1.50 1.60 1.70 0.059 0.063 0.067 e 0.95 BSC. 0.037 e1 1.90 BSC. 0.075 L 0.37 - - 0.015 - - L1 0.60 REF. 0.024 L2 0.25 BSC. 0.010 y - - 0.10 - - 0.004 R 0.10 - - 0.004 - - θ 0o - 8o 0o - 8o

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(2) DFN-6L (2*2 0.75mm)

(Bottom View)

(SIDE View)

Dimensions In Millimeters Dimensions In Inches Symbol

Min. Nom. Max. Min. Nom. Max.

A 0.70 0.75 0.80 0.028 0.030 0.031 A1 0.00 0.02 0.05 0.000 0.001 0.002 A3 0.203 REF 0.008 REF b 0.22 0.275 0.32 0.009 0.011 0.013 D 1.95 2.00 2.05 0.077 0.079 0.081 D2 1.4 1.5 1.60 0.055 0.059 0.063 E 1.95 2.00 2.05 0.077 0.079 0.081 E2 0.8 0.9 1.0 0.031 0.035 0.039 e 0.65 BSC 0.026 BSC

L 0.20 0.3 0.4 0.008 0.012 0.016

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AX3513-V1.2

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