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AP2406
AP2406 1.5Mhz, 600mA Synchronous Step-Down Converter
Description
The AP2406 is a 1.5Mhz constant frequency, slope compensated current mode PWM step-down converter. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode. It is ideal for powering portable equipment that runs from a single cell lithium-Ion (Li+) battery. The AP2406 can supply 600mA of load current from a 2.5V to 5.5V input voltage. The output voltage can be regulated as low as 0.6V. The AP2406 can also run at 100% duty cycle for low dropout operation, extending battery life in portable system. Idle mode operation at light loads provides very low output ripple voltage for noise sensitive applications. The AP2406 is offered in a low profile (1mm) 5-pin, thin SOT package, and is available in an adjustable version and fixed output voltage of 1.2V, 1.5V and 1.8V
MP3 Player Digital Still and Video Cameras Portable Instruments
Features
High Efficiency: Up to 96% 1.5Mhz Constant Switching Frequency 600mA Output Current at VIN=3V Integrated Main switch and synchronous rectifier. No Schottky Diode Required 2.5V to 5.5V Input Voltage Range Output Voltage as Low as 0.6V 100% Duty Cycle in Dropout Low Quiescent Current: 300A Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Short Circuit Protection Thermal Fault Protection <1uA Shutdown Current Space Saving 5-Pin Thin SOT23 package
Applications
Cellular and Smart Phones Microprocessors and DSP Core Supplies Wireless and DSL Modems PDAs
Typical Application
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Figure 1. Basic Application Circuit with AP2406 adjustable version
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(Note 1)
AP2406
Peak SW Sink and Source Current......................1.3A Operating Temperature Range...........-40C to +85C Junction Temperature ............................+125C Storage Temperature Range............-65C to +150C Lead Temperature (Soldering, 10s)................+300C
(Note2)
Absolute Maximum Rating
Input Supply Voltage............................ -0.3V to +6V RUN, V Voltages............................-0.3V to +0.3V SW Voltages..................................-0.3V to V +0.3V P-Channel Switch Source Current (DC)..........800mA N-Channel Switch Sink Current (DC).............800mA
IN FB
Package/Order Information Adjustable Output Version: Fixed Output Versions:
Part Number AP2406ES-ADJ
TSOT23-5 Top Mark Temp Range A1XY -40C to +85C
(Note 3)
Thermal Resistance
Package TSOT23-5
:
JA
Part Number AP2406ES5-1.5 AP2406ES5-1.8 AP2406ES5-1.2
TSOT23-5 Top Mark Temp Range A2XY -40C to +85C A3XY A4XYB
JC
220C/W
110C/W
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ www..com is calculated from the ambient temperature TA and power dissipation PD according to the following formula: AP2406: TJ = TA + (PD)x(220C/W) Note 3: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
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(Note 4)
AP2406
Electrical Characteristics
(V =V
IN RUN
= 3.6V, TA = 25C, unless otherwise noted.) Conditions V =0.5V or V
FB FB IN
Parameter Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Regulated Feedback Voltage V Input Bias Current
MIN 2.5
OUT
TYP
MAX 5.5 400 1.0 0.6120 0.6135 0.6180 30
unit V A A V V V nA %/V V V V % %
=90% 0.5880
V =0V, V =4.2V T = +25C
A A A
300 0.1 0.6000 0.6000 0.6000 0.5865 0.5820
T = 0C T V = 0.65V
A A
85C 85C
T = -40C T
FB FB IN
Reference Voltage Line Regulation Regulated Output Voltage Output Voltage Line Regulation Output Voltage Load Regulation Peak Inductor Current Oscillator Frequency R of P-CH MOSFET
DS(ON) DS(ON)
V = 2.5V to 5.5V, AP2406-1.2, -40C T AP2406-1.5, -40C T VIN = 2.5V to 5.5V 85C 85C 85C 1.164 1.455 1.746
0.04
A A A
0.4 1.236 1.545 1.854 0.40
1.200 1.500 1.800 0.04 0.5
AP2406-1.8, -40C T
V =3V, V =0.5V or V
IN FB
Duty Cycle <35% V =0.6V or V =100%
FB OUT
OUT
=90%
0.75 1.2
1.00 1.5 0.40 0.35 0.01
1.25 1.8 0.50 0.45 1 1.30 1
A MHz A V A
I I
SW SW
= 300mA = -300mA
R
of N-CH MOSFET
SW Leakage RUN Threshold RUN Leakage Current www..com characterization.
VRUN = 0V, VSW= 0V or 5V, VIN = 5V -40C T 85C
A
0.3
1.0 0.01
Note 4: 100% production test at +25C. Specifications over the temperature range are guaranteed by design and
Typical Performance Characteristics (Test Figure 1 above unless otherwise specified)
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AP2406
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Pin Description
PIN 1 2 3 4 5 NAME RUN GND SW IN FB/VOUT
AP2406
FUNCTION Regulator Enable control input. Drive RUN above 1.5V to turn on the part. Drive RUN below 0.3V to turn it off. In shutdown, all functions are disabled drawing <1A supply current. Do not leave RUN floating. Ground Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the drains of the internal P-CH and N-CH MOSFET switches. Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2F or greater ceramic capacitor. VFB (AP2406): Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. VOUT (AP2406ES5-1.5/AP2406ES5-1.8): Output Voltage Feedback Pin. An internal resistive divider divides the output voltage down for comparison to the internal reference voltage.
Functional Block Diagram
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Operation
AP2406
AP2406 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 600mA output current at VIN = 3V with 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 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, ICOMP, 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, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present.
Idle Mode Operation
At very light loads, the AP2406 automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator.
Dropout Operation
When the input voltage decreases toward the value of the output voltage, the AP2406 allows the main switch to remain on for more than one switching cycle and increases the duty cycle (Note 5) until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. Note 5: The duty cycle D of a step-down converter is defined as:
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where TON is the main switch on time, and fOSC is the oscillator frequency (1.5Mhz).
Maximum Load Current
The AP2406 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases.
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Application Information
Figure 2 below shows the basic application circuit with AP2406 fixed output versions.
AP2406
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 (600mA+105mA). Table 1 lists some typical surface mount inductors that meet target applications for the AP2406. Part # L (H) Max DCR (m) Rated D.C. Current (A) 2.52 1.75 1.44 1.15 Size WxLxH (mm)
Sumida CR43 Figure 2. Basic Application Circuit with fixed output versions Setting the Output Voltage Figure 1 above shows the basic application circuit with AP2406 adjustable output version. The external resistor sets the output voltage according to the following equation:
1.4 2.2 3.3 4.7 1.5 2.2 3.3 4.7 1.5 2.2 3.3 4.7
56.2 71.2 86.2 108.7
4.5x4.0x3.5
Sumida CDRH4D18
75 110 162 120 140 180 240
1.32 1.04 0.84 1.29 1.14 0.98 0.79
4.7x4.7x2.0
Toko D312C
3.6x3.6x1.2
R2= 300K for all outputs; R1= 300k for V R1=200k for V and R1=95.3k for V Inductor Selection
OUT
=1.5V, R1=150k for V
OUT
OUT
=1.2V, =1.8V, 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 4.7F ceramic capacitor for most applications is sufficient. 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. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple is determined by: current. The output ripple V
OUT
=2.5V.
OUT
For most designs, the AP2406 operates with inductors of 1H to 4.7H. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be www..com derived from the following equation:
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 35% of the maximum load current 600mA, or =210mA. For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2H. 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
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Package Description
AP2406
Note: Package outline exclusive of mold flash and metal burr.
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