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DUAL CHANNEL1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER
FSP3112
FEATURES
High Efficiency : Up to 96% 1.5MHz Constant Frequency Operation 600mA Output Current at VIN=3.0V Very Low Quiescent Current of 500A No Schottky Diode Required Low RDS(ON) Internal Switches: 0.35 0.6V reference allows low Output Voltage Current Mode Operation for excellent line and load transient Response Short-Circuit &Thermal Fault Protection 1A Shutdown Current Power-on Reset Output Externally Synchronized Oscillator Small Thermally Enhanced MSOP10 and DFN10 Packages
GENERAL DESCRIPTION
The FSP3112 is a dual channel high efficiency monolithic synchronous step down current mode DC-DC converter operating at 1.5MHz constant frequency. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode for each of the channels. The FSP3112 can operate from a 2.5V to 5.5V input voltage and is ideal for powering portable equipment that runs from a single cell lithium-Ion (Li+) battery. It can supply 600mA output current for each channel and can also run at 100% duty cycle for low dropout operation, extending battery life in portable system. For FSP3112, Pulse Skipping Mode operation at light loads provides very low output ripple voltage for noise sensitive applications.
APPLICATIONS
Portable Media Players Digital Still Cameras Cellular Telephones PDAs Wireless and DSL modems
PIN CONFIGURATION
(Top View)
VFB1 1 RUN1 2 VIN 3 SW1 4 GND 5 11 EXPOSED PAD 10 VFB2 9 RUN2 8 POR 7 SW2 6 NC VFB1 1 RUN1 2 VIN 3 SW1 4 GND 5 11 EXPOSED PAD
(Top View)
10 VFB2 9 RUN2 8 POR 7 SW2 6 NC
10-Lead (3mm x3mm) Plastic DFN Exposed Pad is PGND (Pin 11) Must be connected to GND.
10-Lead Plastic MSOP Exposed Pad is PGND (Pin 11) Must be connected to GND.
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FSP3112
PIN DESCRIPTION
Pin Number 1 2 3 4 5 6 7 8 9 10 11 Pin Name VFB1 RUN1 VIN SW1 GND NC SW2 POR RUN2 VFB2 EXPOSED PAD Pin Function Channel 1 output feedback. It receives the feedback voltage from the external resistive divider across the output. Channel 1 Enable Power Supply Channel 1 power switch output Ground No Connection Channel 2 power switch output. Power On Reset. Enable Pin of Channel 2. Channel 2 output feedback. It receives the feedback voltage from the external resistive divider across the output. Power Ground. It must be connect to ground properly.
BLOCK DIAGRAM
SLOPE.COMP
Regulator 1 3 VIN
ISENCE
+ -
600mV
+
EA
+ -
R ICOMP S
Q PWM LOGIC
NON. OVERLAP CONTROL
1 VFB1
-
4 SW1
_Q
OVDET 650mV
+ -
ICMP
+
2 RUN1 9 RUN2 10 VFB2
BANDGAP REFERENCE
OSC
POR COUNTER
8 POR
REGULATOR 2(The same structure as regulator 1)
7 SW2
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FSP3112
ABSOLUTE MAXIMUM RATINGS (NOTE 1)
Parameter Rating Unit Input Supply Voltage -0.3 to +6 V RUN1, RUN2 -0.3 to VIN+0.3 V VFB1, VFB2 Voltages -0.3 to VIN+0.3 V SW1, SW2 Voltages -0.3 to VIN+0.3 V POR Voltages -0.3 to +6 V Peak SW1,SW2 Sink and Source Current 1.5 A -40 to +85 Operating Temperature Range +125 Junction Temperature (Note 2) -65 to 150 Storage Temperature Range +300 Lead Temperature (soldering, 10 sec.) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ=TA+PDxJA
ELECTRICAL CHARACTERISTICS (NOTE 3)
(VIN=VRUN=3.6V, TA=25, Test circuit of Figure 1, Unless otherwise noted) Parameter Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Regulated Feedback Voltage Feedback Pin Input Current Reference Voltage Line Regulation 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 SW Leakage RUN Threshold RUN Leakage Current Condition VFB1=VFB2=0.5V, RUN=0V, VIN=4.2V TA=+25, Channel 1 or 2 TA=0TA85, Channel 1 or 2 TA=-40TA85, Channel 1 or 2 VFB=0.65V VIN=2.5V to 5.5V VIN=2.5V to 5.5V, VOUT=1.8V, IOUT=10mA VIN=3.6V, IOUT=0 to 600mA, VIN=3.0V VFB 1/2= 0.6V ISW=300mA ISW=-300mA VIN=3V,VFB1=VFB2=0.5V, Duty cycle35% VRUN=0V, VSW=0V or 5V, VIN=5V -40TA85 Min. 2.5 Typ. 500 0.3 0.5880 0.5865 0.5850 0.6000 0.6000 0.6000 0.11 0.11 0.0015 600 1.2 1.5 0.35 0.28 1.2 0.3 1.8 0.45 0.45 Max. 5.5 800 2 0.6120 0.6135 0.6150 30 0.40 0.40 Unit V A V V V nA %/V %/V %/mA mA MHz A
A 0.01 1 0.45 1.50 V A 0.1 1 VFBX Ramping Up 8.5 % VFBX Ramping Down, -8.5 % Power-On Reset Threshold (POR) Power-On Reset Delay 175 mS Power-On Reset On-Resistance 100 Note 3: 100% production test at +25. Specifications over the temperature range are guaranteed by design and characterization.
THERMAL RESISTANCE (NOTE 4)
Package JA (/W) MSOP-10 (EXPOSE PAD) 45 DFN-10 (EXPOSE PAD) 45 Note 4: Thermal Resistance is specified with approximately 1 square of 1 oz cooper.
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TYPICAL PERFORMANCE CHARACTERISTICS
(Test Figure 1 below unless otherwise specified)
FSP3112
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TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
FSP3112
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OPERATION
FSP3112
FSP3112 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. For FSP3112 with the Pulse Skipping Mode feature, users can optimize ripple at light load for noise sensitive applications.
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.
PULSE SKIPPING MODE OPERATION
The FSP3112 can automatically switch to Pulse Skipping Mode operation at light load to improve efficiency. In the Pulse Skipping 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 FSP3112 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. 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 FSP3112 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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DUAL CHANNEL1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER
FSP3112
APPLICATION INFORMATION
Fig.1 FSP3112 Typical Application Circuit SETTING THE OUTPUT VOLTAGE The external resistor sets the output voltage according to the following equation:
R2 VOUT = 0.6V 1+ R1
Table 1 ----Resistor select for output voltage setting VOUT 1.2V 1.5V 1.8V 2.5V R1(R3) 316K 316K 316K 316K R2(R4) 316K 474K 634K 1001K
INDUCTOR SELECTION For most designs, the FSP3112 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 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 2.2H. 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 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). Table2 lists some typical surface mount inductors that meet target applications for the FSP3112.
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FSP3112
Part # Sumida CR43 L (H) 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 4.7F 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
FSP3112XXXX Package: MS: MSOP10 L: DFN10 Output Voltage: Blank: ADJ Packing: A: Tape & Reel Temperature Grade: D: -40~85
MARKING INFORMATION
(1) MSOP10 (2) DFN10
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PACKAGE INFORMATION
(1) MSOP10
FSP3112
GAGE PLANE L 0.25
DETAIL A
Symbol A A1 A2 b D E e L y
Dimensions In Millimeters Min. Max. 1.10 0.05 0.15 0.75 0.95 0.17 0.27 2.90 3.10 4.80 5.00 0.50BSC. 0.40 0.70 0.10 0 6
Dimensions In Inches Min. Max. 0.0433 0.0020 0.0060 0.0295 0.0374 0.0067 0.0106 0.1142 0.1220 0.1890 0.1970 0.0197BSC. 0.0157 0.0276 0.0039 0 6
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2) DFN10
FSP3112
Symbol A A1 A3 E E2 D D2 b L p
Min. 0.80 0.00 2.85 1.39 2.85 1.20 0.18 0.30
Dimensions In Millimeters Nom. Max. 0.90 1.00 0.02 0.05 0.20REF 3.00 3.15 2.45 3.00 3.15 1.75 0.25 0.30 0.40 0.50 0.50BSC
Min. 0.031 0.000 0.112 0.055 0.112 0.047 0.008 0.012
Dimensions In Inches Nom. 0.035 0.001 0.008REF 0.118 0.118 0.010 0.016 0.020BSC
Max. 0.039 0.002 0.124 0.096 0.124 0.069 0.015 0.020
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