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TM
MP2105
1MHz, 800mA Synchronous Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
The MP2105 is a 1MHz constant frequency, 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 MP2105 can supply 800mA of load current from a 2.5V to 6V input voltage. The output voltage can be regulated as low as 0.6V. The MP2105 can also run at 100% duty cycle for low dropout applications. The MP2105 is available in a low profile (1mm) 5-pin, TSOT package.
FEATURES
* * * * * * * * * * * * * * * * * High Efficiency: Up to 95% 1MHz Constant Switching Frequency 800mA Available Load Current 2.5V to 6V Input Voltage Range Output Voltage as Low as 0.6V 100% Duty Cycle in Dropout Current Mode Control Short Circuit Protection Thermal Fault Protection <0.1A Shutdown Current Space Saving 5-Pin TSOT23 Package Cellular and Smart Phones Microprocessors and DSP Core Supplies PDAs MP3 Players Digital Still and Video Cameras Portable Instruments
APPLICATIONS
EVALUATION BOARD REFERENCE
Board Number EV2105DJ-00A Dimensions 2.0"X x 2.0"Y x 0.5"Z
"MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
Efficiency vs Load Current
100
INPUT 2.5V to 6V
4 IN SW 3
MP2105
OFF ON
1 EN GND 2 FB 5
EFFICIENCY (%)
OUTPUT 1.8V 800mA
90 80 70 60 50 40 30 20 10 0
VIN = 3.3V VIN = 4.2V
MP2105_TAC_S01
10
100 LOAD CURRENT (mA)
1000
MP2105-EC01
MP2105 Rev. 1.3 5/11/2006
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MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
EN GND SW 1 2 3 4 IN 5 FB
ABSOLUTE MAXIMUM RATINGS (1)
VIN to GND .................................. -0.3V to +6.5V VSW to GND........................... -0.3V to VIN +0.3V VFB, VEN to GND.......................... -0.3V to +6.5V Junction Temperature.............................+150C Lead Temperature ..................................+260C Storage Temperature .............-65C to +150C
Recommended Operating Conditions
(2)
Supply Voltage VIN ............................. 2.5V to 6V Output Voltage VOUT .......................... 0.6V to 6V Operating Temperature .............-40C to +85C
MP2105_PD01_TSOT23-5
Thermal Resistance
Part Number* MP2105DJ * Package TSOT23-5 Temperature -40C to +85C
(3)
TSOT23-5.............................. 220 .... 110.. C/W
Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1" square of 1 oz copper.
JA
JC
For Tape & Reel, add suffix -Z (eg. MP2105DJ-Z) For Lead Free, add suffix -LF (eg. MP2105DJ-LF-Z)
ELECTRICAL CHARACTERISTICS (4)
VIN = VEN = 3.6V, TA = +25C, unless otherwise noted.
Parameter Supply Current Shutdown Current IN Undervoltage Lockout Threshold IN Undervoltage Lockout Hysteresis Regulated FB Voltage FB Input Bias Current PFET On Resistance NFET On Resistance SW Leakage Current PFET Current Limit Oscillator Frequency Thermal Shutdown Trip Threshold EN Trip Threshold EN Input Current fOSC Symbol Condition VEN = VIN, VFB = 0.65V VEN = 0V, VIN = 6V Rising Edge Min Typ 440 0.10 2.30 55 VFB TA = +25C -40C TA +85C VFB = 0.65V ISW = 100mA ISW = -100mA VEN = 0V, VIN = 6V, VSW = 0V or 6V Duty Cycle = 100%, Current Pulse Width < 1ms 0.588 0.582 -50 0.600 0.600 0.5 0.42 0.26 0.612 0.618 +50 Max 600 1 2.40 Units A A V mV V nA A A MHz C 1.5 +1 V A
2.15
-1 1.2 0.85 1.6 1.05 145
+1 2.1 1.25
-40C TA +85C VEN = 0V to 6V
0.3 -1
0.96
Notes: 4) 100% production test at +25C. Specifications over the temperature range are guaranteed by design and characterization.
MP2105 Rev. 1.3 5/11/2006
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TM
MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
TYPCIAL PERFORMANCE CHARACTERISTICS
VIN = 3.3V, VOUT = 1.8V, L1 = 4.7H, C1 = 4.7F, C3 = 10F, TA = +25C, unless otherwise noted.
100 95 90
EFFICIENCY (%)
VIN=3.3V
EFFICIENCY (%)
95 90 85 80 75 70 65 60 55 50 VIN=4.2V VIN=4.2V VIN=3.3V
85 80 75 70 65 60 55 50 10
100 LOAD CURRENT (mA)
1000
10
100 LOAD CURRENT (mA)
1000
MP2105-EC01
MP2105-EC02
Feedback Voltage vs Temperature
SWITCHING FREQUENCY (MHz)
Switching Frequency vs Temperature
1.10 1.08 1.06 1.04 1.02 1.00 0.98 0.96 0.94 -40 -20 0 +20 +40 +60 +80 +100 TEMPERATURE (C)
MP2105-TPC02
0.603
FEEDBACK VOLTAGE (V)
0.602 0.601 0.600 0.599 0.598 0.597 -40 -20 0 +20 +40 +60 +80 +100 TEMPERATURE (C)
MP2105-TPC01
Load Transient
(IOUT=0mA to 500mA step) VOUT 10mV/div. IL 0.2A/div.
Light Load Operation
(IOUT=0mA)
VOUT 100mV/div.
IOUT 0.5A/div.
SW 2V/div.
MP2105-TPC03
MP2105-TPC04
MP2105 Rev. 1.3 5/11/2006
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TM
MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
TYPCIAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 3.3V, VOUT = 1.8V, L1 = 4.7H, C1 = 4.7F, C3 = 10F, TA = +25C, unless otherwise noted.
Heavy Load Operation
IOUT = 800mA VOUT 10mV/div. IL 0.2A/div. VEN 2V/div. VOUT 1V/div.
Startup from Shutdown
SW 2V/div.
IL=0
IL 0.5A/div.
MP2105-TPC07
MP2105-TPC08
Short Circuit Protection (No Load)
VOUT 1V/div. VOUT 1V/div.
Short Circuit Recovery (No Load)
IL 0.5A/div.
IL 0.5A/div.
MP2105-TPC09
MP2105-TPC10
PIN FUNCTIONS
Pin # Name Description EN GND SW IN FB 1 2 3 4 5 Regulator Enable Control Input. Drive EN above 1.5V to turn on the MP2105. Drive EN below 0.3V to turn it off (shutdown current < 0.1A). Ground Power Switch Output. Inductor connection to drains of the internal PFET and NFET switches. Supply Input. Bypass to GND with a 2.2F or greater ceramic capacitor. Feedback Input. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V.
MP2105 Rev. 1.3 5/11/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
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TM
MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
OPERATION
The MP2105 is a constant frequency current mode PWM step-down converter. The MP2105 is optimized for low voltage, Li-Ion battery powered applications where high efficiency and small size are critical. The MP2105 uses an external resistor divider to set the output voltage from 0.6V to 6V. The device integrates both a main switch and a synchronous rectifier, which provides high efficiency and eliminates
IN + IAMP 10X -CURRENT SENSE AMP PWM DH MAIN SWITCH (PCH) PWM CONTROL LOGIC SW SYNCHRONOUS RECTIFIER (NCH) DL
an external Schottky diode. The MP2105 can achieve 100% duty cycle. The duty cycle D of a step-down converter is defined as:
D = TON x fOSC x 100% VOUT x 100% VIN
where TON is the main switch on time, and fOSC is the oscillator frequency (1MHz).
EN
BIAS & VOLTAGE REFERENCE ICS SLOPE COMP EAO
0.6V + FEEDBACK ERROR\ EAMP AMP --
+ + PWMCMP --
FB
CC 17pF
1.0MHz OSCILLATOR
OSC
GND
MP2105_BD01
Figure 1--Functional Block Diagram
MP2105 Rev. 1.3 5/11/2006
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MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER the PFET current limit. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. Short Circuit Protection The MP2105 has short circuit protection. When the output is shorted to ground, the oscillator frequency is reduced to prevent the inductor current from increasing beyond the PFET current limit. The PFET current limit is also reduced to lower the short circuit current. The frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage reaches 0.6V. Maximum Load Current The MP2105 can operate down to 2.5V input voltage; 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.
Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load and line response and protection of the internal main switch and synchronous rectifier. The MP2105 switches at a constant frequency (1MHz) and regulates the output voltage. During each cycle the PWM comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. During normal operation, the main switch 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. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the next cycle starts. Dropout Operation The MP2105 allows the main switch to remain on for more than one switching cycle and increases the duty cycle while the input voltage is dropping close to the output voltage. When the duty cycle reaches 100%, the main switch is held on continuously to deliver current to the output up to
APPLICATION INFORMATION
Output Voltage Setting The external resistor divider sets the output voltage (see Figure 3). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor (see Figure 1). Choose R1 around 500k for optimal transient response. R2 is then given by: R2 = R1 VOUT -1 0.6 V Inductor Selection A 1H to 10H inductor with DC current rating at least 25% higher than the maximum load current is recommended for most applications. For best efficiency, the inductor DC resistance shall be <200m. See Table 2 for recommended inductors and manufacturers. For most designs, the inductance value can be derived from the following equation:
L= VOUT x (VIN - VOUT ) VIN x IL x fOSC
Table 1--Resistor Selection vs. Output Voltage Setting
VOUT 1.2V 1.5V 1.8V 2.5V R1 499k (1%) 499k (1%) 499k (1%) 499k (1%) R2 499k (1%) 332k (1%) 249k (1%) 158k (1%)
where IL is Inductor Ripple Current. Choose inductor ripple current approximately 30% of the maximum load current, 800mA. The maximum inductor peak current is:
IL(MAX ) = ILOAD + IL 2
Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Table 3 lists inductors recommended for this purpose.
MP2105 Rev. 1.3 5/11/2006
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MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
Table 2--Suggested Surface Mount Inductors
Manufacturer
Coilcraft Toko Sumida
Part Number
D01605T-472 D52LC CR43-4R7
Inductance (H)
4.7 4.7 4.7
Max DCR ()
0.150 0.087 0.109
Saturation Current (A)
1.20 1.14 1.15
Dimensions L x W x H (mm3)
5.4 x 4.2 x 1.8 5x5x2 4.3 x 4.8 x 3.5
Table 3--Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Manufacturer
Coilcraft Murata Sumida Sumida
Part Number
DO1605T-103MX LQH4C100K04 CR32-100 CR54-100
Inductance (H)
10 10 10 10
Max DCR ()
0.3 0.2 0.2 0.1
Saturation Current (A)
1.0 1.2 1.0 1.2
IRMS (A)
0.9 0.8 0.7 1.4
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. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a 4.7F capacitor is sufficient. Output Capacitor Selection The output capacitor keeps output voltage ripple small and ensures regulation loop stable. The output capacitor impedance shall be low at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended. The output ripple VOUT is approximately:
VOUT VOUT x (VIN - VOUT ) 1 x ESR + VIN x fOSC x L 8 x fOSC x C3
PC Board Layout The high current paths (GND, IN and SW) should be placed very close to the device with short, direct and wide traces. Input capacitor C1 needs to be as close as possible to the IN and GND pins. The external feedback resistors shall be placed next to the FB pin. Keep the switching node SW short and away from the feedback network. Figure 2 illustrates an example of PCB layout and signal routing.
Figure 2--MP2105 Suggested Layout
MP2105 Rev. 1.3 5/11/2006
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TM
MP2105 - 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
PACKAGE INFORMATION
TSOT23-5
NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications.
MP2105 Rev. 1.3 5/11/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
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