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Features
* * * * * * * * * * * * * * *
MCP1601
Description
The MCP1601 is a fully integrated synchronous BUCK (step down) DC/DC converter for battery powered systems. With an input operating range of 2.7V to 5.5V, the MCP1601 is ideal for applications being powered by one single cell Li-Ion, 2 to 3 cell NiMH, NiCd or alkaline sources. Output voltages can range from 0.9V to VIN to accommodate a wide range of applications. Efficiency can exceed 92% while operating at 750 kHz with load current capability up to 500 mA. The MCP1601 is used to minimize space, cost and wasted energy. The PWM mode switching frequency is internally set to a fixed 750 kHz allowing the use of low profile, surface mount inductors and ceramic capacitors while maintaining a typical efficiency of 92%. The MCP1601 is capable of three distinct operating modes: PWM, PFM and Low Drop Out. When operating in PWM (pulse width modulation) mode, the DC/DC converter switches at a single high frequency determined by either the internal 750 kHz oscillator or external synchronization frequency. For applications that operate at very light to no load for extended periods of time, the MCP1601 is capable of operating in PFM (pulse frequency modulation mode) to reduce the number of switching cycles/sec and consume less energy. The third mode of operation (LDO mode) occurs when the input voltage approaches the output voltage and the BUCK duty cycle approaches 100%. The MCP1601 will enter a low drop out mode and the high-side P-Channel BUCK switch will saturate, providing the output with the maximum voltage possible. The MCP1601 has integrated over-current protection, over-temperature protection and UVLO (Under Voltage Lockout) to provide for a fail safe solution with no external components. The MCP1601 is available in the 8-pin MSOP package, with an operating temperature range of -40C to +85C.
500 mA Synchronous BUCK Regulator
Input Range of 2.7V to 5.5V 3 Operating Modes: PWM, PFM and LDO Integrated BUCK and Synchronous Switches Ceramic or Electrolytic Input/Output Filtering Capacitors 750 kHz Fixed Switching Frequency Oscillator Synchronization to 1 MHz PWM Mode Auto-Switching from PWM/PFM Operation 100% Duty Cycle Capable for Low Input Voltage 500 mA Continuous Output Current Capability Integrated Under-Voltage Lock-Out Protection Integrated Over-Temperature Protection Integrated Soft Start Circuitry Low Output Voltage Capability to 0.9V Temperature Range: -40C to +85C Small 8-Pin MSOP Package
Applications
* * * * * * Low Power Handheld CPUs and DSPs Cellular Phones Organizers and PDAs Digital Cameras +5V or +3.3V Distributed Voltages USB Powered Devices
Package Type
8-Pin MSOP
VIN SHDN FB AGND 1 2 3 4 8 LX PGND VOUT SYNC/PWM
MCP1601
7 6 5
2003 Microchip Technology Inc.
DS21762A-page 1
MCP1601
Typical Application
Typical Application (2.7V to 4.2V)
L Range 10 H to 22 H 10 H VOUT Range 1.2V to 3.3V IOUT = 0 mA to 400 mA COUT 10 F COUT Range 10 F to 47 F C1 47 pF R1 250 k (for 1.8V)
MCP1601
1 VIN 2 SHDN Input Voltage 2.7V-4.2V CIN 10 F 3 FB 4 AGND LX 8 PGND 7 VOUT 6 SYNC/ 5 PWM
R2 200 k
Functional Block Diagram
VIN UVLO SHDN Internal Circuit Enable Duty Clamp Cycle Enable Out Internal Band Gap Reference Buffered 0.8V Output VOUT
10 pF FB 3 M 0.8V
800 k 12 pF RCOMP C COMP EA + AGND
+
VREF
Soft Start Duty Cycle Clamp 10% - 90% PWM Latch R
-
ISENSEP + -
Feedforward Oscillator K*VIN SQW S
OUT
Inset Timing
LX
ISENSEP VREF
-
ISENSEN PFM Mode Timing PGND PGND
PFM Comparator
+
VREF ISENSEN AGND AGND VREF
-
-
SYNC/PWM
DS21762A-page 2
2003 Microchip Technology Inc.
MCP1601
1.0 ELECTRICAL CHARACTERISTICS PIN FUNCTION TABLE
NAME VIN SHDN FB AGND VOUT SYNC/PWM PGND LX FUNCTION Input Source Voltage Device Shutdown Pin Output Voltage Feedback Input Analog Ground Sensed Output Voltage Synchronous Clock input or PWM/ PFM select Power Ground Output Inductor Node
Absolute Maximum Ratings
VIN - AGND ......................................................................6.0V SHDN, FB, SYNC/PWM, VOUT ..... (AGND-0.3V) to (VIN+0.3V) LX to PGND................................................ -0.3V to (VIN+0.3V) PGND to AGND .................................................. -0.3V to +0.3V Output Short Circuit Current .................................continuous Storage temperature .....................................-65C to +150C Ambient Temp. with Power Applied ................-40C to +85C Operating Junction Temperature...................-40C to +125C ESD protection on all pins .................................................. 4 kV Notice: Stresses above those listed under "Maximum ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operational listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL SPECIFICATIONS
Electrical Specifications: Unless otherwise indicated, VIN=4.2V, VOUT=1.8V, ILOAD = 10 mA, TA=-40C to +85C. Parameters Power Input Requirements Voltage Shutdown Current PFM Mode Current Oscillator Section Internal Oscillator Frequency External Oscillator Capture Range External Oscillator Duty Cycle Internal Power Switches RDSon P-CHANNEL RDSon N-CHANNEL Dropout Voltage Pin Leakage Current Output PWM Mode Peak Current Limit Output Voltage Output Voltage Range Reference Feedback Voltage Feedback Input Bias Current Line Regulation Load Regulation Start-Up Time VOUT VFB IVFB VLINE-REG VLOAD-REG TSTART 0.9 0.78 -- -- -- -- -- 0.8 0.1 0.1 1.5 0.5 VIN 0.82 -- -- -- -- V V nA %/V % ms VIN=2.7V to 5.5V, ILOAD=10 mA VIN = 3.6V, ILOAD = 0 mA to 300 mA PWM Mode, SYNC/PWM=VIN IPEAK-PWM -- 1.0 -- A PWM Mode, SYNC/PWM = VIN, TA = +25C RDSon-P RDSon-N VDROPOUT ILX -- -- -- -1.0 500 500 250 -- -- -- -- 1.0 m m mV A IP=100 mA, TA=+25C, VIN=4.2V IN=100 mA, TA=+25C, VIN =4.2V VOUT = 2.7V, ILOAD = 300 mA, TA=+25C, VDROPOUT=97%VOUT SHDN = 0V, VIN = 5.5V, LX = 0V, LX = 5.5V FOSC FSYNC FSYN-FALL 650 850 10 750 -- -- 850 1000 90 kHz kHz % SYNC/PWM = VIN FSYNC > FOSC FSYNC = 1 MHz VIN I(VIN) I(VIN) 2.7 -- -- -- 0.05 119 5.5 1.0 180 V A A ILOAD = 0 mA to 500 mA Shutdown Mode (SHDN = GND) SYNC/PWM = GND, PFM Mode (ILOAD = 0 mA) Sym Min Typ Max Units Conditions
2003 Microchip Technology Inc.
DS21762A-page 3
MCP1601
ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Specifications: Unless otherwise indicated, VIN=4.2V, VOUT=1.8V, ILOAD = 10 mA, TA=-40C to +85C. Parameters Protection Features Average Short Circuit Current Under-Voltage Lockout Under-Voltage Lockout Hysteresis Thermal Shutdown Thermal Shutdown Hysteresis Interface Signals (SHDN, SYNC/PWM) Logic Low Input Logic High Input Input Leakage Current VIN-HIGH VIN-HIGH IIN-LK -- 45 -- -- -- -- 15 -- 0.1 % of VIN % of VIN A UVLO UVLO-HYS TSHD TSHD-HYS -- 2.4 -- -- -- 890 -- 190 160 10 -- 2.7 -- -- -- mA V mV C C RLOAD < 1 ohm For VIN decreasing Sym Min Typ Max Units Conditions
TEMPERATURE SPECIFICATIONS
Electrical Specifications: Unless otherwise noted, all parameters apply at VDD = 2.7V to 5.5V Parameters Temperature Ranges Specified Temperature Range Operating Junction Temperature Range Storage Temperature Range Thermal Package Resistances Thermal Resistance, 8 Pin MSOP
JA
Symbol
Min
Typ
Max
Units
Conditions
TA TJ TA
-40 -40 -65 --
-- -- -- 208
+85 +125 +150 --
C C C C/W Single-Layer SEMI G42-88 Board, Natural Convection
DS21762A-page 4
2003 Microchip Technology Inc.
MCP1601
2.0
Note:
TYPICAL PERFORMANCE CURVES
The graphs and tables provided following this note are a statistical summary based on a limited number of samples and are provided for informational purposes only. The performance characteristics listed herein are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 H, COUT= 10 F (X5R Ceramic), CIN = 10 F (X5R Ceramic), SYNC/PWM=VIN.
PFM Mode Quiescent Current (A) 100 90 Efficiency (%) 80 70 60 50 40 0 100 200 300 400 500 Load Current (mA)
VIN = 4.2V VIN = 3.6V VIN = 2.7V
VOUT = 1.2V Auto PWM/PFM
130
VOUT = 1.8V PFM Mode ILOAD = 0 TA = + 25C TA = + 85C
120
110
TA = + 0C TA = - 40C
100 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V)
FIGURE 2-1: (VOUT = 1.2V).
110 100 Efficiency (%) 90 80
VIN = 4.2V
Efficiency vs. Load Current
FIGURE 2-4: PFM Mode Quiescent Current vs. Input Voltage.
Internal Oscillator Frequency (kHz) 780.0 760.0
TA = - 40C
VOUT = 1.8V Auto PWM/PFM
ILOAD = 10 mA Forced PWM Mode
TA = 0C
740.0 720.0 700.0 680.0 2.7 3.1 3.5 3.9 4.3
TA = + 125C
VIN = 3.6V VIN = 2.7V
70 60 50 0 100 200
TA = + 25C
300
400
500
4.7
5.1
5.5
Load Current (mA)
Input Voltage (V)
FIGURE 2-2: (VOUT = 1.8V).
110 100 Efficiency (%) 90
VIN = 4.5V
Efficiency vs. Load Current
FIGURE 2-5: Input Voltage.
1.300 1.275 Output Voltage (V) 1.250 1.225 1.200 1.175 1.150 1.125 1.100
Oscillator Frequency vs.
VOUT = 3.3V Auto PWM/PFM
VOUT = 1.2V Auto PWM/PFM
VIN = 5.0V
VIN = 3.6V VIN = 2.7V
80 70 60 50 0
VIN = 5.5V
VIN = 4.2V
100
200
300
400
500
0
100
200
300
400
500
Load Current (mA)
Load Current (mA)
FIGURE 2-3: (VOUT = 3.3V).
Efficiency vs. Load Current
FIGURE 2-6: Current.
Output Voltage vs. Load
2003 Microchip Technology Inc.
DS21762A-page 5
MCP1601
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 H, COUT= 10 F (X5R Ceramic), CIN = 10 F (X5R Ceramic), SYNC/PWM=VIN.
1.820
VIN = 2.7V
4.5 LX Leakage Current (nA)
VOUT = 1.8V Auto PWM/PFM
VIN = 5.0V
Output Votlage (V)
1.800 1.780 1.760 1.740 1.720 1.700 0 100 200 300
VIN = 3.6V
3.0
VIN = 4.2V
1.5
Synchronous NChannel BUCK Switch PChannel
0.0 400 500 -40 -15 10 35 60 85 Load Current (mA) Ambient Temperature (C)
FIGURE 2-7: Current.
3.35 3.33 3.30 3.28 3.25 3.23 3.20 3.18 3.15 3.13 3.10 0 100
Output Voltage vs. Load
FIGURE 2-10: Temperature.
Switch Leakage vs.
VOUT = 3.3V Auto PWM/PFM
Output Voltage (V)
VIN = 4.5V VIN = 5.0V VIN = 5.5V
200
300
400
500
Load Current (mA)
FIGURE 2-8: Current.
450 Dropout Voltage (mV) 400 350 300 250 200 150 100 50 0 0 100
Output Voltage vs. Load
FIGURE 2-11: Typical PWM Mode of Operation Waveforms.
Dropout = (VIN-VOUT) in mV @ 97% of VOUT
VOUT = 2.7V
VOUT = 3.3V
200
300
400
500
Load Current (mA)
FIGURE 2-9: Input to Output Voltage Differential for 100% Duty Cycle vs. Load Current.
FIGURE 2-12: Typical PFM Mode of Operation Waveforms.
DS21762A-page 6
2003 Microchip Technology Inc.
MCP1601
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 H, COUT= 10 F (X5R Ceramic), CIN = 10 F (X5R Ceramic), SYNC/PWM=VIN.
FIGURE 2-13: Typical Startup From Shutdown Waveform.
FIGURE 2-16: to PWM).
Load Step Response (PFM
FIGURE 2-14:
Startup From 0V Input.
FIGURE 2-17: (Forced PWM).
Line Step Response
FIGURE 2-15: (Forced PWM).
Load Step Response
FIGURE 2-18: Mode).
Line Step Response (PFM
2003 Microchip Technology Inc.
DS21762A-page 7
MCP1601
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 H, COUT= 10 F (X5R Ceramic), CIN = 10 F (X5R Ceramic), SYNC/PWM=VIN.
FIGURE 2-19: Typical Output Ripple Voltage (Forced PWM Mode).
FIGURE 2-21: Synchronization.
External Oscillator
FIGURE 2-20: Typical Output Ripple Voltage (PFM Mode).
DS21762A-page 8
2003 Microchip Technology Inc.
MCP1601
3.0 PIN FUNCTIONS
PIN FUNCTION TABLE
Function Input Voltage Shutdown Input Feedback Input Analog Ground Return Oscillator Synchronization or PWM/ PFM Select Mode Input Sensed Output Voltage Input Power Ground Return BUCK Inductor Output
3.5
TABLE 3-1:
Pin 1 2 3 4 5 6 7 8
Oscillator Synchronization or PWM/ PFM Select Mode Input (SYNC/PWM)
Name VIN SHDN FB AGND SYNC/ PWM VOUT PGND LX
Connect an external oscillator to SYNC/PWM to synchronize. With an external oscillator present, the device is forced into a PWM-only mode of operation. For internal oscillator operation, the SYNC/PWM pin is tied high to operate in a forced PWM-only mode and low for a PWM/PFM mode of operation.
3.6
Output Voltage Sense (VOUT) Power Ground Return (PGND)
Connect the output voltage directly to VOUT for sensing.
3.7
3.1
Input Voltage (VIN)
Connect all large signal ground returns to PGND. (See Section 5.6, "Printed Circuit Board Layout", for details).
Connect the unregulated input voltage source to VIN. If the input voltage source is located more than several inches away, or is a battery, a typical input capacitor of 10 F is recommended.
3.8
BUCK Inductor Connection (LX)
3.2
Shutdown Input (SHDN)
Connect LX directly to the BUCK inductor. This pin carries large signal-level currents and all connections should be as short and wide as possible. (See Section 5.6, "Printed Circuit Board Layout", for details).
Connect SHDN to a logic low input to force the device into a shutdown low quiescent current mode. When in shutdown, both the P-Channel and N-Channel switches are turned off, in addition to the internal oscillator and other circuitry. When connected to a logic high input, the device will operate in the selected mode.
3.3
Feedback Input (FB)
Connect FB to an external resistor divider to set output voltage regulation. The feedback pin is typically equal to 0.8V. See Section 5.0, "Applications Information", for details in selecting feedback resistors.
3.4
Analog Ground Return (AGND)
Tie all small signal ground returns to AGND. (See Section 5.6, "Printed Circuit Board Layout", for details).
2003 Microchip Technology Inc.
DS21762A-page 9
MCP1601
4.0 DEVICE OPERATION
4.1.2
The MCP1601 is a synchronous DC/DC converter with integrated switches. Developed to provide high efficiency across a wide line and load range, the MCP1601 integrates the three modes of operation described below. In addition to three operating modes, the MCP1601 also integrates many features that minimize external circuitry, saving board space and cost. With two external resistors used to set the output voltage, the MCP1601 output is adjustable from 0.9V to VIN.
PULSE FREQUENCY MODULATION (PFM) MODE
4.1
Operating Modes
The MCP1601 has three distinct modes of operation, with each one optimized for a specific operating condition commonly encountered in handheld portable power applications.
4.1.1
FEEDFORWARD VOLTAGE PULSE WIDTH MODULATION (PWM) MODE
The MCP1601 is also capable of operating in a pulse frequency modulation mode. This mode of operation is desired for applications that have very long periods of inactivity and the output current requirement placed on the MCP1601 is very low. By entering the PFM mode of operation, the switching frequency becomes mainly a function of load current and will decrease as the load current decreases. By switching slower, the energy used turning "on" and "off" the high-side P-Channel and low-side N-Channel is reduced, making the PFM mode more efficient with light output load currents. When load activity is encountered, the MCP1601 will automatically switch from the PFM mode to the fixed frequency PWM mode by sensing the increase in load current. The auto PWM/PFM mode is selected by placing a logic low at the SYNC/PWM input pin. If an external clock is used to synchronize the MCP1601 switching frequency, the PFM mode is automatically disabled. To enter the PFM mode of operation, the SYNC/PWM pin must be held to a logic low level and the peak inductor current, sensed internal to the MCP1601, is below the internal PFM threshold for more than 1024 clock cycles. If both of these conditions are met, the MCP1601 will enter the PFM mode. While in the PFM mode, the MCP1601 will disable the low-side N-Channel switch to optimize efficiency at low operating currents. A cycle will begin by turning on the high-side P-Channel switch and will end when the output voltage exceeds a predetermined voltage set point. If the peak inductor current exceeds the internal PFM mode current threshold prior to the output voltage exceeding the voltage set point, the load current has increased and the MCP1601 will automatically switch to PWM operation. The typical hysteresis on the PFM comparator is 6 mV. The typical output ripple voltage is below 40 mV when using a 10 H inductor and 10 F ceramic output capacitor when VIN = 4.2V. For proper PFM mode operation, the value of the external inductor and the external capacitor should be the same. For example, when using a 10 H inductor, a 10 F capacitor should be used. When using a 22 H inductor, a 22 F capacitor should be used.
The Pulse Width Modulation (PWM) mode of operation is desired when operating from typical to maximum output currents with the proper head room voltage at the input. This mode of operation optimizes efficiency and noise by switching at a fixed frequency. Typical output ripple voltage is less than 10 mV when using a 10 H inductor and 10 F ceramic capacitor. The internal operating frequency of the MCP1601 is 750 kHz, nominal. The duty cycle, or "ON" time, of the high-side, integrated, P-Channel MOSFET is determined by the continuous mode BUCK transfer function. For the continuous inductor current case, the duty cycle can be approximated by VOUT/VIN. The integrated high-side BUCK P-Channel switch will conduct for the "on" time. At the end of the "on" time, the high-side P-Channel switch is turned off and the integrated, low-side, NChannel synchronous switch is turned on to freewheel the inductor current. The PWM mode architecture employed in the MCP1601 is a feedforward voltage mode control and feeds the input voltage into the PWM oscillator ramp. This information is used to quickly change the operating duty cycle in the event of a sudden input voltage change. The effects on the output voltage are minimized. To force the MCP1601 into PWM mode, the SYNC/PWM pin should be tied to a logic high. The forced PWM mode should be used for applications that require the fastest transient response from light load to heavy load or applications that require a single switching frequency independent of load. An external oscillator between 850 kHz and 1 MHz can be connected to the SYNC/PWM pin for synchronization to an external clock source. The MCP1601 will always operate in the PWM mode when synchronized to an external oscillator.
4.1.3
LOW DROP OUT (LDO) MODE
When the input voltage to the MCP1601 is decreasing and approaches the set output voltage level, the duty cycle increases to a maximum of 90% (typically). To continue to regulate the output to as high a voltage as possible, the MCP1601 enters the low drop out mode of operation. In this mode, the high-side P-Channel MOSFET acts like a saturated LDO. This mode allows the operation of the load circuitry down to the minimum input supply that is typical in battery-powered applications.
DS21762A-page 10
2003 Microchip Technology Inc.
MCP1601
4.2 Cross-Conduction Timing 4.3.3 INTERNAL SOFT START
Proper timing between turning on the P-Channel, highside MOSFET and turning off the N-Channel, low-side MOSFET (and vice versa) is critical to obtaining high efficiency. This delay between transitions is what limits the maximum duty cycle obtainable by the MCP1601. The delay between transitions leads to more time when the external inductor current is freewheeling through the internal N-Channel body diode and leads to a decrease in efficiency. If the timing delay is too short and both the internal P-Channel MOSFET and NChannel MOSFET conduct, high peak currents will be observed shooting through the device. This will also reduce the operating efficiency. The MCP1601 inset timing is integrated to optimize efficiency for the entire line and load operating range of the device. The MCP1601 completely integrates the soft start function and requires no external components. The soft start time is typically 0.5 ms and is reset during overcurrent and over-temperature shutdown.
4.3.4
OVER-TEMPERATURE PROTECTION
The MCP1601 protects the internal circuitry from overtemperature conditions by sensing the internal device temperature and shutting down when it reaches approximately 160C. The device will shut down, the temperature will cool to approximately 150C, soft start will be enabled and normal operation will resume with no external circuit intervention.
4.3 4.3.1
Integrated Protection Features SHUTDOWN
4.3.5
UNDER-VOLTAGE LOCKOUT
By placing a logic low on the SHDN pin of the MCP1601, the device will enter a low quiescent current shutdown mode. This feature turns off all of the internal bias and drivers within the MCP1601 in an effort to minimize the quiescent current. This feature is popular for battery-operated, portable power applications. The shutdown low quiescent current is typically 1 A.
Protection from operating at sustained input voltages that are out of range is prevented with the integrated Under-Voltage Lockout feature. When the input voltage dips below 2.5V (typically), the MCP1601 will shutdown and the soft start circuit will be reset. Normal operation will resume when the input voltage is elevated above 2.7V, maximum. This hysteresis is provided to prevent the device from starting with too low of an input voltage.
4.3.2
INTERNAL OSCILLATOR AND SYNCHRONIZATION CAPABILITY
The internal oscillator is completely integrated and requires no external components. The frequency is set nominally to 750 kHZ in an effort to minimize the external inductor and capacitor size needed for the BUCK topology. In addition to the internal 750 kHz oscillator, the MCP1601 is capable of being synchronized to an external oscillator. The external oscillator frequency must be greater than 850 kHz and less than 1 MHz. For proper synchronization, the duty cycle of the external synchronization clock must be between 10% and 90%. The minimum low voltage level should be below 15% of VIN and the high level of the clock should be above 45% of VIN. Rise and fall time requirements for the external synchronization clock must be faster than 100 ns from 10% to 90%. When synchronizing to an external clock, the MCP1601 will always operate in the PWM mode in an effort to eliminate multiple switching frequency's and their harmonics.
2003 Microchip Technology Inc.
DS21762A-page 11
MCP1601
5.0 APPLICATIONS INFORMATION
MCP1601 Application Circuit
L Range 10 H to 22 H 10 H VOUT Range 1.2V to 3.3V IOUT = 0 mA to 400 mA COUT 10 F COUT Range 10 F to 47 F C1 47 pF 1 M For VOUT < 1.2V ONLY R2 200 k R1 250 k (for 1.8V)
MCP1601
1 VIN 2 SHDN Input Voltage 2.7V-4.2V CIN 10 F 3 FB 4 AGND LX 8 PGND 7 VOUT 6 SYNC/ 5 PWM
FIGURE 5-1:
Typical Application Circuit. 5.1.1 LEAD CAPACITOR
5.1
Setting Output Voltage
The MCP1601 output voltage is set by using two external resistors for output voltages 1.2V. For output voltages < 1.2V, a third 1 M series resistor is necessary to compensate the control system. A 200 k resistor is recommended for R2, the lower end of the voltage divider. Using higher value resistors will make the circuit more susceptible to noise on the FB pin, causing unstable operation. Lower value resistors can be used down to 20 k or below, if necessary. The feedback reference voltage for the MCP1601 is typically 0.8V. The equation used to calculate the output voltage is shown below.
Capacitor C1 is used for applications that utilize ceramic output capacitors. To lower the PFM mode ripple voltage, a 47 pf capacitor for C1 is used to couple the output AC ripple voltage to the internal PFM mode comparator. For PWM mode, only applications that use electrolytic capacitors that have 0.2 or greater of ESR (Equivalent Series Resistance), C1 is not necessary.
5.2
5.2.1
Choosing External Components
CAPACITORS
EQUATION
R1 = R2 x [ ( VOUT V FB ) - 1 ] Where: VOUT is the desired output voltage, VFB is the MCP1601 internal feedback reference voltage R1 is the resistor connected to VOUT in the voltage divider R2 is the resistor connected to ground in the voltage divider Example: Desired VOUT = 2.5V VFB = 0.8V R2 = 200 k R1 = 425 k
The MCP1601 was developed to take full advantage of the latest ceramic capacitor technology, though electrolytic types can be used as well. When selecting the best capacitor for the application, the capacitance, physical size, ESR, temperature coefficient, ripple current ratings (electrolytic) and cost are considered in making the best choice. When selecting ceramic capacitors for COUT, the temperature coefficient of the dielectric should be evaluated. Two dielectrics are recommended as they are stable over a wide temperature range (X5R and X7R). Other dielectrics can be used, but their capacitance should stay within the recommended range over the entire operating temperature range.
DS21762A-page 12
2003 Microchip Technology Inc.
MCP1601
5.2.1.1 Input
For all BUCK-derived topologies, the input current is pulled from the source in pulses, placing some burden on the input capacitor. For most applications, a 10 F ceramic capacitor connected to the MCP1601 input is recommended to filter the current pulses. Less capacitance can be used for applications that have low source impedance. The ripple current ratings for ceramic capacitors are typically very high due to their low loss characteristics. Lower-cost electrolytic capacitors can be used, but ripple current ratings should not be exceeded. The maximum peak inductor current is equal to the maximum DC output current plus 1/2 the peak-to-peak AC ripple current in the inductor. The AC ripple current in the inductor can be calculated using the following relationship.
EQUATION
VL = L x Solving for IL: dI dt
5.2.1.2
Output
EQUATION
IL = ( VL L ) x t Where: t is equal to the "on" time of the P-Channel switch and, VL = the voltage across the inductor (VIN - VOUT) Example: VIN = VOUT = FSW = 3.6V 1.8V 750 kHz equal to the
For BUCK-derived topologies, the output capacitor filters the continuous AC inductor ripple current while operating in the PWM mode. Typical inductor AC ripple current for the MCP1601 is 120 mA peak-to-peak with a 3.6V input, 10 H inductor for a 1.8V output application. Using an output capacitor with 0.3 of ESR, the output ripple will be approximately 36 mV. The recommended range for the output capacitor is from 10 F (20%) to 47 F (20%). Larger value capacitors can be used, but require evaluation of the control system stability.
EQUATION
V Ripple = ILRipple x COUTesr The above equation assumes that the output capacitance is large enough so that the ripple voltage (as a result of charging and discharging the capacitor) is negligible and can be used for applications that use electrolytic capacitors with esr > 0.3. When using a 10 F ceramic X5R dielectric capacitor, the output ripple voltage is typically less than 10 mV.
IOUT(MAX) = 300 mA The approximate "on" time is Duty Cycle (VOUT / VIN) x 1/FSW. TON = TON = VL = IL = IL = IL(PEAK) = IL(PEAK) = IL(PEAK) = 667 ns 3.6V - 1.8V = 1.8V (1.8V/10 H) x 667 ns 120 mA IOUTMAX + 1/2 IL 300 mA + (120 mA) / 2 360 mA
(1.8V/3.6V) x 1/(750 kHz)
5.2.2
BUCK INDUCTOR
There are many suppliers and choices for selecting the BUCK inductor. The application, physical size requirements (height vs. area), current rating, resistance, mounting method, temperature range, minimum inductance and cost all need to be considered in making the best choice. When choosing an inductor for the MCP1601 Synchronous BUCK, there are two primary electrical specifications to consider. 1. 2. Current rating of the inductor. Resistance of the inductor.
When selecting a BUCK inductor, many suppliers specify a maximum peak current.
Many suppliers of inductors rate the maximum RMS (Root Mean Square) current. The BUCK inductor RMS current is dependent on the output current, inductance, input voltage, output voltage and switching frequency. For the MCP1601, the inductor RMS current over the 2.7V to 5.5V input range, 0.9V to 5V output voltage range is no more than 15% higher than the average DC output current for the minimum recommended inductance of 10 H 20%. When selecting an inductor that has a maximum RMS current rating, use a simple approximation that the RMS current is 1.2 times the maximum output current. Example: IOUT(MAX) = 300 mA, the inductor should have an RMS rating > 360 mA (1.2 x IOUT(MAX)).
2003 Microchip Technology Inc.
DS21762A-page 13
MCP1601
DC resistance is another common inductor specification. The MCP1601 will work properly with inductor DC resistance down to 0. The trade-off in selecting an inductor with low DC resistance is size and cost. To lower the resistance, larger wire is used to wind the inductor. The switch resistance in the MCP1601 is approximately 0.5. Inductors with DC resistance lower than 0.1 will not have a significant impact on the efficiency of the converter.
5.4
Passive Component Suppliers
CERAMIC CAPACITOR SUPPLIERS
Type Description Ceramic 10 F 0805 X5R 6.3V #GRM21BR60J106K Ceramic 10 F 1206 X5R 6.3V #GRM319R60J106K Ceramic 10 F 1210 X5R 6.3V JMK325BJ106MD Ceramic 10 F 0805 X5R 6.3V #08056D106MAT4A Ceramic 10 F 1206 X5R 6.3V #12066D106MAT4A Ceramic 10 f 1210 6.3V #C1210C106M9PAC Ceramic 22 F 1206 X5R 6.3V GRM31CR60J226ME20B Ceramic 22 F 1210 X5R 6.3V JMK325BJ226MY
TABLE 5-2:
Supplier Murata(R) Murata(R) Taiyo YudenTM AVXTM AVXTM Kemet(R) Murata(R) Taiyo YudenTM Note:
5.3
L and COUT Combinations
When selecting the L-COUT output filter components, the inductor value range is limited from 10 H to 22 H. However, when using the larger inductor values, larger capacitor values should be used. The following table lists the recommended combinations of L and COUT.
TABLE 5-1:
L 10 H 15 H 22 H Note:
L-COUT COMBINATIONS
COUT 10 F to 47 F 15 F to 47 F 22F to 47 F
For proper PFM mode operation, the value of the external inductor and the external capacitor should be the same. For example, when using a 10 H inductor, a 10 F capacitor should be used. When using a 22 H inductor, a 22 F capacitor should be used.
Taiyo Yuden 1210 is a low profile case (1.15 mm)
TABLE 5-3:
Supplier Kemet
(R)
ELECTROLYTIC CAPACITOR SUPPLIERS
Type Description Tantalum 47 F D Case 200 M 10V #T495D476M010AS Tantalum 47 F C Case 300 M 6.3V #TPSC476M006S300 Tantalum 47 F C Case 110 M 16V 594D47X0016C2T Tantalum 22 F B Case 380 M 6.3V 594D226X06R3B2T Tantalum 15 F B Case 500 M 10V 594D156X0010B2T
AVXTM Sprague(R) Sprague(R) Sprague(R)
DS21762A-page 14
2003 Microchip Technology Inc.
MCP1601
TABLE 5-4:
Supplier Sumida(R) Sumida(R) Sumida(R) CT* Coilcraft Coilcraft
(R)
INDUCTOR SUPPLIERS
L 10 H 10 H 10 H 10 H 10 H 15 H 22 H 10 H 15 H 10 H Type Unshielded Shielded Shielded Shielded Shielded Shielded Shielded Unshielded Wafer Unshielded Wafer Shielded Area (mm) 4.1 mm x 3.8 mm 4.0 mm x 4.0 mm 5.7 mm x 5.7 mm 7.3 mm x 7.3 mm 6.6 mm x 4.5 mm 6.6 mm x 4.5 mm 6.6 mm x 4.5 mm 6.0 mm x 5.4 mm 6.0 mm x 5.4 mm 5.0 mm x 5.0 mm Height (mm) 3.0 mm 1.8 mm 3.0 mm 3.5 mm 3.0 mm 3.0 mm 3.0 mm 1.3 mm 1.3 mm 2.0 mm DC Resistance 230 M 160 M 65 M 70 M 75 M 90 M 110 M 300 M 380 M 66 M Max. Current 0.76A 0.66A 1.3A 1.7A 1.0A 0.8A 0.7A 0.60A 0.55A 0.7A Series C32 CDRH3D16 CDRH5D28 CTCDRH73 DS1608 DS1608 DS1608 LPO6013 LPO6013 NP04SB100M
Coilcraft(R)
(R)
Coilcraft(R) Coilcraft(R) Taiyo YudenTM Note:
CT* = Central Technologies
5.5
Efficiency
5.6
Printed Circuit Board Layout
Efficiency will be affected by the external component selection and the specific operating conditions for the application. In Section 2.0, "Typical Performance Curves", there are curves plotted using typical inductors that can be used to estimate the converter efficiency for 1.2V, 1.8V and 3.3V.
The MCP1601 is capable of switching over 500 mA at 750 kHz. As with all high-frequency, switch mode, power supplies, a good board layout is essential to preventing the noise generated by the power train switching from interfering with the sensing circuitry. The MCP1601 has not demonstrated a sensitivity to layout, but good design practice will prevent undesired results.
MCP1601 CIN
PGND AGND
COUT
PGND
C1 R2 SILK
FIGURE 5-2:
AGND
R1
Component Placement.
When designing a board layout for the MCP1601, the first thing to consider is the physical placement of the external components. In Figure 5-2, SM0805 10 F ceramic capacitors are used for CIN and COUT. The SM0603 package is used for R1, R2 and C1. The inductor used is the Coilcraft(R) LPO2506 series low profile (0.047" high). The board outline in this example is 1" x 1". CIN, L and COUT are positioned around the MCP1601 to make the high current paths as short as possible.
2003 Microchip Technology Inc.
DS21762A-page 15
MCP1601
MCP1601
PGND PGND
AGND
BOT
AGND
FIGURE 5-3:
Top Layer.
FIGURE 5-4:
Bottom Layer.
The top layer of the board layout is shown in Figure 5-3. The power conversion process is made up of two types of circuits. One circuit carries changing large signals (current, voltage), like CIN, COUT, L and the VIN, LX PGND pins of the MCP1601. The other circuitry is much smaller in signal and is used to sense, regulate and control the high-power circuitry. These components are R1, R2, C1 and pins FB, AGND. The top layer is partitioned so that the larger signal connections are short and wide, while the smaller signals are routed away from the large signals. The MCP1601 utilizes two ground pins to separate the large signal ground current from the small signal circuit ground. The large signal ("Power Ground") is labeled "PGND". The small signal is labeled "Analog Ground" or "AGND". In Figure 5-3, the PGND and the AGND are kept separate on the top layer.
In Figure 5-4, the bottom layer is a partitioned ground plane that connects AGND to PGND near the input capacitor. The large signal current will circulate on the top PGND partition. The lower partition is used for a "quiet" ground, where AGND is connected.
DS21762A-page 16
2003 Microchip Technology Inc.
MCP1601
6.0
6.1
PACKAGING INFORMATION
Package Marking Information
8-Lead MSOP
Example:
XXXXXX YWWNNN
1601I 344025
Legend:
XX...X Customer specific information* YY Year code (last 2 digits of calendar year) WW Week code (Week of January 1 is week `01) NNN Alphnumeric traceability code
Note:
In the event the full Microchip part number cannot be marked on one line, it will be carried over to the next line thus limiting the number of available characters for customer specific information.
*
Standard device marking consists of Microchip part number, year code, week code, and traceability code.
2003 Microchip Technology Inc.
DS21762A-page 17
MCP1601
8-Lead Plastic Micro Small Outline Package (MS) (MSOP)
E E1 p
D 2 B n 1
A c
A2
A1
(F)
L
Units Number of Pins Pitch Overall Height Molded Package Thickness Standoff Overall Width Molded Package Width Overall Length Foot Length Footprint (Reference) Foot Angle Lead Thickness Lead Width Mold Draft Angle Top Mold Draft Angle Bottom *Controlling Parameter Significant Characteristic Notes: Dimension Limits n p A A2 A1 E E1 D L F c B
INCHES MIN NOM 8 .026 .044 .030 .002 .184 .114 .114 .016 .035 0 .004 .010 .006 .012 7 7 .193 .118 .118 .022 .037 .034 .038 .006 .200 .122 .122 .028 .039 6 .008 .016 MAX MIN
MILLIMETERS* NOM 0.65 1.18 0.76 0.05 4.67 2.90 2.90 0.40 0.90 0 0.10 0.25 0.15 0.30 7 7 4.90 3.00 3.00 0.55 0.95 0.86 0.97 0.15 .5.08 3.10 3.10 0.70 1.00 6 0.20 0.40 MAX 8
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed .010" (0.254mm) per side. Drawing No. C04-111
DS21762A-page 18
2003 Microchip Technology Inc.
MCP1601
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. PART NO. Device X Temperature Range /XX Package Examples:
a) b) MCP1601-I/MS: 8LD MSOP package. MCP1601T-I/MS: Tape and Reel, 8LD MSOP package.
Device:
MCP1601: 500 mA Synchronous BUCK Regulator MCP1601T: 500 mA Synchronous BUCK Regulator Tape and Reel
Temperature Range:
I
= -40C to +85C
Package:
MS = Plastic Micro Small Outline (MSOP), 8-lead
Sales and Support
Data Sheets Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recommended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following: 1. 2. 3. Your local Microchip sales office The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277 The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using. Customer Notification System Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
2003 Microchip Technology Inc.
DS21762A-page19
MCP1601
NOTES:
DS21762A-page 20
2003 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices: * * Microchip products meet the specification contained in their particular Microchip Data Sheet. Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip's Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. Microchip is willing to work with the customer who is concerned about the integrity of their code. Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as "unbreakable."
*
* *
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break microchip's code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip's products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights.
Trademarks The Microchip name and logo, the Microchip logo, KEELOQ, MPLAB, PIC, PICmicro, PICSTART, PRO MATE and PowerSmart are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Accuron, dsPIC, dsPICDEM.net, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, microPort, Migratable Memory, MPASM, MPLIB, MPLINK, MPSIM, PICC, PICkit, PICDEM, PICDEM.net, PowerCal, PowerInfo, PowerTool, rfPIC, Select Mode, SmartSensor, SmartShunt, SmartTel and Total Endurance are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. Serialized Quick Turn Programming (SQTP) is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. (c) 2003, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona in July 1999 and Mountain View, California in March 2002. The Company's quality system processes and procedures are QS-9000 compliant for its PICmicro(R) 8-bit MCUs, KEELOQ(R) code hopping devices, Serial EEPROMs, microperipherals, non-volatile memory and analog products. In addition, Microchip's quality system for the design and manufacture of development systems is ISO 9001 certified.
2003 Microchip Technology Inc.
DS21762A - page 21
M
WORLDWIDE SALES AND SERVICE
AMERICAS
Corporate Office
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ASIA/PACIFIC
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EUROPE
Austria
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Microchip Ltd. 505 Eskdale Road Winnersh Triangle Wokingham Berkshire, England RG41 5TU Tel: 44 118 921 5869 Fax: 44-118 921-5820
12/05/02
DS21762A-page 22
2003 Microchip Technology Inc.

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