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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER
FSP3100
FEATURES
High Efficiency : Up to 96% 1.5MHz Constant Switching Frequency 600mA Output Current at VIN=3.0V 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 : 300uA 1uA Shutdown Current Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Short Circuit and Thermal Fault Protection Space Saving 5-pin SOT23 packages
GENERAL DESCRIPTION
The FSP3100 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 FSP3100 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 FSP3100 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 FSP3100 is offered in a low profile (1mm) 5-pin, SOT package, and is available in an adjustable version and fixed output voltage of 1.2V, 1.5V and 1.8V.
APPLICATIONS
Cellular and Smart Phones PDAs MP3 Player Digital Still and Video Cameras Portable instruments Microprocessors and DSP Core Supplies Wireless and DSL Modems
PIN CONFIGURATION
(Top View)
Run GND
1 2 3
5
VFB/VOUT
SW
4
VIN
PIN DESCRIPTION
Pin Number 1 2 3 4 Pin Name RUN GND SW IN Pin 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 disable drawing 1uA supply current. Do not leave RUN floating. Ground Power Switch Output. It is the Switch node 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, pin2, with a 2.2uF or greater ceramic capacitor. VFB (FSP3100): Feedback Input Pin. Connected FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. VOUT (FSP3100-1.2/1.5/1.8): Output Voltage Feedback Pin. An internal resistive divider divides the output voltage down for comparison to the internal reference voltage.
5
FB/VOUT
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER BLOCK DIAGRAM
FSP3100
For Adjustable Output R1+R2 is external.
THERMAL RESISTANCE (NOTE 1)
Package JA (/W) SOT23-5L 250 Note 1: Thermal Resistance is specified with approximately 1 square of 1 oz cooper. JC (/W) 110
ABSOLUTE MAXIMUM RATINGS (NOTE 2)
Parameter Rating Unit Input Supply Voltage -0.3 to +6 V RUN, VFB Voltages -0.3 to VIN +0.3 V -0.3 to VIN+0.3 V SWVout Voltages Peak SW Sink and Source Current 1.5 A -40 to +85 Operating Temperature Range +125 Junction Temperature (Note 3) -65 to 150 Storage Temperature Range +300 Lead Temperature ( solding, 10 sec.) Note 2: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 3: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ=TA+PDxJA
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (NOTE 4)
(VIN=VRUN=3.6V, TA=25, Unless otherwise noted) Parameter Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Regulated Feedback Voltage VFB Input Bias Current Reference Voltage Line Regulation Regulated Output Voltage Output Voltage Line Regulation Output Voltage Load Regulation Maximum Output Current Oscillator Frequency RDS(ON) of P-CH MOSFET RDS(ON) of N-CH MOSFET Peak Inductor Current Condition VFB=0.5V VFB=0V, VIN=4.2V TA=+25 TA=0TA85 TA=-40TA85 VFB=0.65V VIN=2.5V to 5.5V, VOUT=VFB (R2=0) FSP3100C12AD: -40TA85 FSP3100C15AD: -40TA85 FSP3100C18AD: -40TA85 VIN=2.5V to 5.5V, IOUT=10mA IOUT from 0 to 600mA VIN=3.0V VFB=0.6V or VOUT=100% ISW=300mA ISW=-300mA VIN=3V, VFB=0.5V or VOUT=90%, Duty Cycle35% VRUN=0V, VSW=0V or 5V, VIN=5V VOVL=VOVL-VFB -40TA85 0.5880 0.5865 0.5850 Min. 2.5 Typ. 270 0.08 0.6000 0.6000 0.6000 0.11 1.200 1.500 1.800 0.11 0.0015 1.5 0.30 0.20 1.20 Max. 5.5 400 1.0 0.6120 0.6135 0.6150 30 0.40 1.236 1.545 1.854 0.40 1.8 0.50 0.45 Unit V uA V V V nA %/V V V V %/V %/mA mA MHz A
FSP3100
1.164 1.455 1.746
600 1.2
SW Leakage uA 0.01 1 60 mV Output over voltage lockout 0.3 0.45 1.30 V RUN Threshold RUN Leakage Current uA 0. 1 1 Note 4: 100% production test at +25. Specifications over the temperature range are guaranteed by design and characterization.
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS
(Test Figure 1 below unless otherwise specified)
FSP3100
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
FSP3100
Output Voltage (V)
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
FSP3100
Frequency (MHz)
RDS(ON) (OHM)
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TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
FSP3100
Input Current (mA)
Load Transient Response PWM Mode Only
Supply Current (A)
Load Transient Response Idle Mode to PWM Mode
PWM
Idle Mode
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER OPERATION
FSP3100
FSP3100 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 suppliers 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 faults is no longer present.
IDLE MODE OPERATION
At very light loads, the FSP3100 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 FSP3100 allows the main switch to remain on for more than one switching cycle and increases the duty cycle until it reaches 100%. The duty cycle D of a step-down converter is defined as:
D=TON x f OSC x 100%
VOUT x 100% VIN
Where TON is the main switch on time and fOSC is the oscillator frequency (1.5MHz). 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 increase, 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.
MAXIMUM LOAD CURRENT
The FSP3100 will operate with input supply voltages 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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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER APPLICATION INFORMATION
Vin 2.7V-4.2V C1 4.7uF 1 Run GND 2 VFB 5 R2 632K R1 316K 4 Vin SW 3 L1 2.2uH C2 22pF Vout 1.8V C3 10uF
FSP3100
Fig.1 Basic Application Circuit with FSP3100 adjustable version
3 L1 2.2uH
Vin 2.5V-5.5V C1 4.7uF
4
Vin
SW
Vout 1.8V C3 10uF
1
Run GND 2
Vout
5
Fig.2 Basic Application Circuit with fixed output versions SETTING THE OUTPUT VOLTAGE Figure 1 above shows the basic application circuit with FSP3100 adjustable output version. The external resistor sets the output voltage according to the following equation:
R2 VOUT = 0.6V 1+ R1
R1=300k for all outputs; R2=300k for VOUT=1.2V, R2=200k for VOUT=1.5V, R2=150k for VOUT=1.8V and R=95.3k for VOUT=2.5V. INDUCTOR SELECTION For most designs, the FSP3100 operates with inductors of 1uH to 4.7uH. 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:
L=
VOUT x ( VIN - VOUT ) VIN x I L x f OSC
Where IL 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 IL=210mA. For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2uH. 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 (600mA+105mA). Table 1 lists some typical surface mount inductors that meet target applications for the FSP3100.
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FSP3100
Part # Sumida CR43 L (uH) 14 2.2 3.3 4.7 1.5 2.2 3.3 4.7 1.5 2.2 3.3 4.7 Max DCR (m) 56.2 71.2 86.2 108.7 75 110 162 120 140 180 240 Rated D.C. Current (A) 2.52 1.75 1.44 1.15 1.32 1.04 0.84 1.29 1.14 0.98 0.79 Size WxLxH (mm)
4.5x4.0x3.5
Sumida CDRH4D18
4.7x4.7x2.0
Toko D312C
3.6x3.6x1.2
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 minimum 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 4.7uF ceramic capacitor for most applications is sufficient. OUTPUT CAPACITOR SELECTION The output capacitor is requires 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. The output ripple VOUT is determined by:
VOUT
VOUT x ( VIN - VOUT ) 1 x ESR + VIN x f OSC x L 8 x f OSC x C3
ORDERING INFORMATION
FSP3100XXXX Package: C: SOT23-5L Output Voltage: Blank: ADJ 12: 1.2V 15: 1.5V 18: 1.8V Packing: A: Tape & Reel Temperature Grade: D: -40~85
MARKING INFORMATION
AXXXX
Internal Code (if needed) Date code: X: Year (1=2001) X: Week (A~Z,a~z; 0~52) Output Voltage: 1: ADJ 2: 1.5V 3: 1.8V 4: 1.2V Part Number: FSP3100
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1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER
PACKAGE INFORMATION
FSP3100
D
e1
5
4
E1 E
A2 A1 A
1
e
2
3
b
C L L1
Symbol A A1 A2 b C D E E1 L L1 e e1
Dimensions In Millimeters Min. Max. 0.900 1.250 0.000 0.100 0.900 1.150 0.300 0.400 0.100 0.200 2.820 3.020 2.650 2.950 1.500 1.700 0.300 0.600 0.700REF 0.95 Bsc. 1.90 Bsc. 0 8
Dimensions In Inches Min. Max. 0.036 0.050 0.000 0.004 0.041 0.045 0.012 0.016 0.004 0.008 0.111 0.119 0.104 0.116 0.060 0.068 0.012 0.024 0.028REF 0.038 Bsc. 0.076 Bsc. 0 8
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