MICROCHIP MCP1601

M
MCP1601
500 mA Synchronous BUCK Regulator
Features
Description
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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.
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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: -40°C to +85ºC
Small 8-Pin MSOP Package
Applications
•
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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
1
8
LX
SHDN
2
7
PGND
FB
3
6
VOUT
AGND
4
5
SYNC/PWM
MCP1601
 2003 Microchip Technology Inc.
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 -40°C to +85°C.
DS21762A-page 1
MCP1601
Typical Application
Typical Application (2.7V to 4.2V)
MCP1601
1 VIN
2 SHDN
Input
Voltage
2.7V-4.2V
CIN
10 µF
3 FB
4 AGND
VOUT Range
1.2V to 3.3V
IOUT = 0 mA to 400 mA
L Range
10 µH to 22 µH
10 µH
LX 8
COUT
10 µF
PGND 7
VOUT 6
SYNC/ 5
PWM
COUT Range
10 µF to 47 µF
R1
250 kΩ
(for 1.8V)
C1
47 pF
R2
200 kΩ
Functional Block Diagram
VIN
UVLO
Internal
Circuit
Enable
SHDN
10 pF
FB
3 MΩ
0.8V
800 kΩ 12 pF
RCOMP C
COMP
Enable Out
Duty
Clamp
Cycle
Internal
Band Gap
Reference
Buffered 0.8V Output
+
VREF
-
Soft Start
ISENSEP
EA
+
+
-
AGND
Duty
Cycle
Clamp
10% - 90%
PWM Latch
R
Feedforward Oscillator
K*VIN
OUT
SQW
LX
Inset
Timing
S
ISENSEN
ISENSEP
VREF
VOUT
-
PFM Comparator
PFM Mode
Timing
PGND
+
VREF
-
PGND
ISENSEN
AGND
VREF
-
SYNC/PWM
AGND
DS21762A-page 2
 2003 Microchip Technology Inc.
MCP1601
1.0
ELECTRICAL
CHARACTERISTICS
PIN FUNCTION TABLE
NAME
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 .....................................-65°C to +150°C
Ambient Temp. with Power Applied ................-40°C to +85°C
Operating Junction Temperature...................-40°C to +125°C
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.
FUNCTION
VIN
Input Source Voltage
SHDN
Device Shutdown Pin
FB
Output Voltage Feedback Input
AGND
Analog Ground
VOUT
Sensed Output Voltage
SYNC/PWM
Synchronous Clock input or PWM/
PFM select
PGND
Power Ground
LX
Output Inductor Node
ELECTRICAL SPECIFICATIONS
Electrical Specifications: Unless otherwise indicated, VIN=4.2V, VOUT=1.8V, ILOAD = 10 mA, TA=-40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
Conditions
VIN
2.7
—
5.5
V
Shutdown Current
I(VIN)
—
0.05
1.0
µA
Shutdown Mode (SHDN = GND)
PFM Mode Current
I(VIN)
—
119
180
µA
SYNC/PWM = GND, PFM Mode
(ILOAD = 0 mA)
Internal Oscillator Frequency
FOSC
650
750
850
kHz
SYNC/PWM = VIN
External Oscillator Capture Range
FSYNC
850
—
1000
kHz
FSYNC > FOSC
FSYN-FALL
10
—
90
%
FSYNC = 1 MHz
RDSon P-CHANNEL
RDSon-P
—
500
—
mΩ
IP=100 mA, TA=+25°C, VIN=4.2V
RDSon N-CHANNEL
RDSon-N
—
500
—
mΩ
IN=100 mA, TA=+25°C, VIN =4.2V
VDROPOUT
—
250
—
mV
VOUT = 2.7V, ILOAD = 300 mA,
TA=+25°C, VDROPOUT=97%VOUT
ILX
-1.0
—
1.0
µA
SHDN = 0V, VIN = 5.5V, LX = 0V, LX =
5.5V
IPEAK-PWM
—
1.0
—
A
PWM Mode, SYNC/PWM = VIN, TA =
+25°C
Power Input Requirements
Voltage
ILOAD = 0 mA to 500 mA
Oscillator Section
External Oscillator Duty Cycle
Internal Power Switches
Dropout Voltage
Pin Leakage Current
Output PWM Mode
Peak Current Limit
Output Voltage
Output Voltage Range
Reference Feedback Voltage
VOUT
0.9
—
VIN
V
VFB
0.78
0.8
0.82
V
IVFB
—
0.1
—
nA
Line Regulation
VLINE-REG
—
0.1
—
%/V
Load Regulation
VLOAD-REG
—
1.5
—
%
VIN = 3.6V,
ILOAD = 0 mA to 300 mA
TSTART
—
0.5
—
ms
PWM Mode, SYNC/PWM=VIN
Feedback Input Bias Current
Start-Up Time
 2003 Microchip Technology Inc.
VIN=2.7V to 5.5V, ILOAD=10 mA
DS21762A-page 3
MCP1601
ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Specifications: Unless otherwise indicated, VIN=4.2V, VOUT=1.8V, ILOAD = 10 mA, TA=-40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
—
UVLO
2.4
890
—
mA
—
2.7
V
UVLO-HYS
TSHD
—
190
—
mV
—
160
—
°C
TSHD-HYS
—
10
—
°C
Logic Low Input
VIN-HIGH
—
—
15
% of
VIN
Logic High Input
VIN-HIGH
45
—
—
% of
VIN
IIN-LK
—
—
0.1
µA
Conditions
Protection Features
Average Short Circuit Current
Under-Voltage Lockout
Under-Voltage Lockout Hysteresis
Thermal Shutdown
Thermal Shutdown Hysteresis
RLOAD < 1 ohm
For VIN decreasing
Interface Signals (SHDN, SYNC/PWM)
Input Leakage Current
TEMPERATURE SPECIFICATIONS
Electrical Specifications: Unless otherwise noted, all parameters apply at VDD = 2.7V to 5.5V
Parameters
Symbol
Min
Typ
Max
Units
Specified Temperature Range
TA
-40
—
+85
°C
Operating Junction Temperature Range
TJ
-40
—
+125
°C
Storage Temperature Range
TA
-65
—
+150
°C
θJA
—
208
—
°C/W
Conditions
Temperature Ranges
Thermal Package Resistances
Thermal Resistance, 8 Pin MSOP
DS21762A-page 4
Single-Layer SEMI G42-88
Board, Natural Convection
 2003 Microchip Technology Inc.
MCP1601
2.0
TYPICAL PERFORMANCE CURVES
Note:
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.
100
VOUT = 1.2V
Auto PWM/PFM
Efficiency (%)
90
80
70
VIN = 3.6V
VIN = 4.2V
60
VIN = 2.7V
50
40
0
100
200
300
400
PFM Mode Quiescent Current
(µA)
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 µH, COUT= 10 µF (X5R Ceramic), CIN = 10 µF (X5R
Ceramic), SYNC/PWM=VIN.
130
VOUT = 1.8V
PFM Mode
ILOAD = 0
TA = + 25°C
120
TA = + 85°C
TA = + 0°C
110
TA = - 40°C
100
500
2.7
3.1
3.5
Load Current (mA)
Efficiency vs. Load Current
110
VOUT = 1.8V
Auto PWM/PFM
Efficiency (%)
100
90
80
VIN = 4.2V
VIN = 3.6V
70
VIN = 2.7V
60
50
0
100
200
300
400
780.0
740.0
TA = + 125°C
720.0
TA = + 25°C
700.0
680.0
3.1
90
VIN = 5.0V
80
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
FIGURE 2-5:
Input Voltage.
VIN = 5.5V
70
60
Oscillator Frequency vs.
1.300
VOUT = 3.3V
Auto PWM/PFM
VIN = 4.5V
5.5
TA = - 40°C
2.7
VOUT = 1.2V
Auto PWM/PFM
1.275
Output Voltage (V)
Efficiency (%)
100
5.1
760.0
500
Efficiency vs. Load Current
110
4.7
TA = 0°C
ILOAD = 10 mA
Forced PWM Mode
Load Current (mA)
FIGURE 2-2:
(VOUT = 1.8V).
4.3
FIGURE 2-4:
PFM Mode Quiescent
Current vs. Input Voltage.
Internal Oscillator Frequency
(kHz)
FIGURE 2-1:
(VOUT = 1.2V).
3.9
Input Voltage (V)
1.250
1.225
VIN = 3.6V
VIN = 2.7V
1.200
1.175
1.150
VIN = 4.2V
1.125
50
1.100
0
100
200
300
400
500
0
FIGURE 2-3:
(VOUT = 3.3V).
Efficiency vs. Load Current
 2003 Microchip Technology Inc.
100
200
300
400
500
Load Current (mA)
Load Current (mA)
FIGURE 2-6:
Current.
Output Voltage vs. Load
DS21762A-page 5
MCP1601
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 µH, COUT= 10 µF (X5R Ceramic), CIN = 10 µF (X5R
Ceramic), SYNC/PWM=VIN.
Output Votlage (V)
VIN = 2.7V
1.800
VOUT = 1.8V
Auto PWM/PFM
1.780
1.760
VIN = 3.6V
1.740
VIN = 4.2V
1.720
1.700
LX Leakage Current (nA)
4.5
1.820
VIN = 5.0V
3.0
1.5
Synchronous NChannel
BUCK Switch PChannel
0.0
0
100
200
300
400
500
-40
Load Current (mA)
Output Voltage (V)
FIGURE 2-7:
Current.
10
35
60
85
Ambient Temperature (°C)
Output Voltage vs. Load
3.35
3.33
3.30
3.28
3.25
3.23
3.20
3.18
3.15
3.13
3.10
-15
FIGURE 2-10:
Temperature.
Switch Leakage vs.
VOUT = 3.3V
Auto PWM/PFM
VIN = 4.5V
VIN = 5.0V
VIN = 5.5V
0
100
200
300
400
500
Load Current (mA)
FIGURE 2-8:
Current.
Dropout Voltage (mV)
450
Output Voltage vs. Load
FIGURE 2-11:
Typical PWM Mode of
Operation Waveforms.
Dropout = (VIN-VOUT) in mV @ 97% of VOUT
400
350
VOUT = 2.7V
300
250
VOUT = 3.3V
200
150
100
50
0
0
100
200
300
400
500
Load Current (mA)
FIGURE 2-9:
Input to Output Voltage
Differential for 100% Duty Cycle vs. Load
Current.
DS21762A-page 6
FIGURE 2-12:
Typical PFM Mode of
Operation Waveforms.
 2003 Microchip Technology Inc.
MCP1601
Note: Unless otherwise indicated, VIN = 4.2V, VOUT = 1.8V, L = 10 µH, COUT= 10 µF (X5R Ceramic), CIN = 10 µF (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 µH, COUT= 10 µF (X5R Ceramic), CIN = 10 µF (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
TABLE 3-1:
3.5
PIN FUNCTION TABLE
Pin
Name
Function
1
VIN
2
SHDN
Shutdown Input
3
FB
Feedback Input
Input Voltage
Analog Ground Return
Oscillator Synchronization or
PWM/ PFM Select Mode Input
(SYNC/PWM)
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.
4
AGND
5
SYNC/
PWM
6
VOUT
Sensed Output Voltage Input
Connect the output voltage directly to VOUT for sensing.
7
PGND
Power Ground Return
3.7
8
LX
BUCK Inductor Output
3.1
Oscillator Synchronization or
PWM/ PFM Select Mode Input
Input Voltage (VIN)
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 µF is recommended.
3.2
Shutdown Input (SHDN)
3.6
Output Voltage Sense (VOUT)
Power Ground Return (PGND)
Connect all large signal ground returns to PGND. (See
Section 5.6, “Printed Circuit Board Layout”, for details).
3.8
BUCK Inductor Connection (LX)
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
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.
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 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 µH
inductor and 10 µF 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.
DS21762A-page 10
4.1.2
PULSE FREQUENCY MODULATION
(PFM) 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 µH inductor and 10 µF 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 µH inductor, a 10 µF capacitor should be
used. When using a 22 µH inductor, a 22 µF capacitor
should be used.
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.
 2003 Microchip Technology Inc.
MCP1601
4.2
Cross-Conduction Timing
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.
4.3
4.3.1
Integrated Protection Features
SHUTDOWN
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 µA.
4.3.2
4.3.3
INTERNAL SOFT START
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 160°C. The device will shut down, the
temperature will cool to approximately 150°C, soft start
will be enabled and normal operation will resume with
no external circuit intervention.
4.3.5
UNDER-VOLTAGE LOCKOUT
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.
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
MCP1601
1 VIN
2 SHDN
Input
Voltage
2.7V-4.2V
CIN
10 µF
3 FB
4 AGND
L Range
10 µH to 22 µH
10 µH
LX 8
COUT
10 µF
PGND 7
VOUT 6
SYNC/ 5
PWM
COUT Range
10 µF to 47 µF
C1
47 pF
1 MΩ
5.1
R1
250 kΩ
(for 1.8V)
R2
200 kΩ
For VOUT < 1.2V ONLY
FIGURE 5-1:
VOUT Range
1.2V to 3.3V
IOUT = 0 mA to 400 mA
Typical Application Circuit.
Setting Output Voltage
5.1.1
LEAD CAPACITOR
The MCP1601 output voltage is set by using two external resistors for output voltages ≥ 1.2V. For output voltages < 1.2V, a third 1 MΩ series resistor is necessary
to compensate the control system. A 200 kΩ 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 kΩ or below, if necessary.
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 0.2Ω or greater of ESR
(Equivalent Series Resistance), C1 is not necessary.
The feedback reference voltage for the MCP1601 is
typically 0.8V. The equation used to calculate the
output voltage is shown below.
5.2.1
EQUATION
R1 = R2 × [ ( 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:
5.2
Choosing External Components
CAPACITORS
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.
Desired VOUT = 2.5V
VFB = 0.8V
R2 = 200 kΩ
R1 = 425 kΩ
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 µF
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.
5.2.1.2
Output
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 µH inductor for a 1.8V output application. Using an output capacitor with 0.3Ω of ESR, the
output ripple will be approximately 36 mV.
The recommended range for the output capacitor is
from 10 µF (±20%) to 47 µF (±20%). Larger value
capacitors can be used, but require evaluation of the
control system stability.
EQUATION
V Ripple = ILRipple × 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 > 0.3Ω.
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 ×
dI
dt
Solving for ∆IL:
EQUATION
∆IL = ( VL ⁄ L ) × ∆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 =
3.6V
VOUT =
1.8V
FSW =
750 kHz
IOUT(MAX) = 300 mA
The approximate “on” time is
Duty Cycle (VOUT / VIN) x 1/FSW.
equal
TON =
(1.8V/3.6V) x 1/(750 kHz)
TON =
667 ns
VL =
3.6V - 1.8V = 1.8V
∆IL =
(1.8V/10 µH) x 667 ns
∆IL =
120 mA
When using a 10 µF ceramic X5R dielectric capacitor,
the output ripple voltage is typically less than 10 mV.
IL(PEAK) =
5.2.2
IL(PEAK) =
300 mA + (120 mA) / 2
IL(PEAK) =
360 mA
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.
to
the
IOUTMAX + 1/2 ∆IL
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 µH ±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 0Ω. 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 0.5Ω. Inductors with DC resistance
lower than 0.1Ω will not have a significant impact on the
efficiency of the converter.
5.3
L and COUT Combinations
When selecting the L-COUT output filter components,
the inductor value range is limited from 10 µH to 22 µH.
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:
Note:
L-COUT COMBINATIONS
L
COUT
10 µH
10 µF to 47 µF
15 µH
15 µF to 47 µF
22 µH
22µF to 47 µF
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 µH inductor, a 10 µF
capacitor should be used. When using a
22 µH inductor, a 22 µF capacitor should
be used.
5.4
Passive Component Suppliers
TABLE 5-2:
Supplier
Type
Description
Murata®
Ceramic 10 µF 0805 X5R 6.3V
#GRM21BR60J106K
Murata®
Ceramic 10 µF 1206 X5R 6.3V
#GRM319R60J106K
Taiyo
Yuden™
Ceramic 10 µF 1210 X5R 6.3V
JMK325BJ106MD
AVX™
Ceramic 10 µF 0805 X5R 6.3V
#08056D106MAT4A
AVX™
Ceramic 10 µF 1206 X5R 6.3V
#12066D106MAT4A
Kemet®
Ceramic 10 µf 1210 6.3V
#C1210C106M9PAC
Murata®
Ceramic 22 µF 1206 X5R 6.3V
GRM31CR60J226ME20B
Taiyo
Yuden™
Ceramic 22 µF 1210 X5R 6.3V
JMK325BJ226MY
Note:
Taiyo Yuden 1210 is a low profile case
(1.15 mm)
TABLE 5-3:
Supplier
®
DS21762A-page 14
CERAMIC CAPACITOR
SUPPLIERS
ELECTROLYTIC CAPACITOR
SUPPLIERS
Type
Description
Kemet
Tantalum 47 µF D Case 200 MΩ 10V
#T495D476M010AS
AVX™
Tantalum 47 µF C Case 300 MΩ 6.3V
#TPSC476M006S300
Sprague®
Tantalum 47 µF C Case 110 MΩ 16V
594D47X0016C2T
Sprague®
Tantalum 22 µF B Case 380 MΩ 6.3V
594D226X06R3B2T
Sprague®
Tantalum 15 µF B Case 500 MΩ 10V
594D156X0010B2T
 2003 Microchip Technology Inc.
MCP1601
TABLE 5-4:
INDUCTOR SUPPLIERS
Supplier
L
Type
Area (mm)
Height
(mm)
DC
Resistance
Max.
Current
Sumida®
10 µH
Unshielded
4.1 mm x 3.8 mm
3.0 mm
230 MΩ
0.76A
C32
Sumida®
10 µH
Shielded
4.0 mm x 4.0 mm
1.8 mm
160 MΩ
0.66A
CDRH3D16
Series
Sumida®
10 µH
Shielded
5.7 mm x 5.7 mm
3.0 mm
65 MΩ
1.3A
CDRH5D28
CT*
10 µH
Shielded
7.3 mm x 7.3 mm
3.5 mm
70 MΩ
1.7A
CTCDRH73
®
10 µH
Shielded
6.6 mm x 4.5 mm
3.0 mm
75 MΩ
1.0A
DS1608
Coilcraft®
15 µH
Shielded
6.6 mm x 4.5 mm
3.0 mm
90 MΩ
0.8A
DS1608
®
22 µH
Shielded
6.6 mm x 4.5 mm
3.0 mm
110 MΩ
0.7A
DS1608
Coilcraft®
10 µH
Unshielded
Wafer
6.0 mm x 5.4 mm
1.3 mm
300 MΩ
0.60A
LPO6013
Coilcraft®
15 µH
Unshielded
Wafer
6.0 mm x 5.4 mm
1.3 mm
380 MΩ
0.55A
LPO6013
Taiyo
Yuden™
10 µH
Shielded
5.0 mm x 5.0 mm
2.0 mm
66 MΩ
0.7A
NP04SB100M
Coilcraft
Coilcraft
Note:
5.5
CT* = Central Technologies
Efficiency
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.
5.6
Printed Circuit Board Layout
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
COUT
CIN
PGND
AGND
C1
PGND
R1
R2
SILK
FIGURE 5-2:
AGND
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 µF
ceramic capacitors are used for CIN and COUT. The
SM0603 package is used for R1, R2 and C1. The inductor used is the Coilcraft® 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
FIGURE 5-3:
Top 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.
FIGURE 5-4:
AGND
Bottom 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.
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.
DS21762A-page 16
 2003 Microchip Technology Inc.
MCP1601
6.0
PACKAGING INFORMATION
6.1
Package Marking Information
8-Lead MSOP
XXXXXX
YWWNNN
Legend:
Note:
*
Example:
1601I
344025
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
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
α
A2
A
c
φ
A1
(F)
L
β
Units
Number of Pins
Pitch
Dimension Limits
n
p
Overall Height
MILLIMETERS*
INCHES
MIN
MAX
NOM
MIN
NOM
0.65
.026
.044
A
1.18
.038
0.76
.006
0.05
.193
.200
.114
.118
.114
.118
L
.016
.035
Foot Angle
F
φ
Lead Thickness
c
.004
Lead Width
B
α
.010
Mold Draft Angle Top
Mold Draft Angle Bottom
β
Molded Package Thickness
A2
.030
Standoff
A1
.002
E
.184
Molded Package Width
E1
Overall Length
D
Foot Length
Footprint (Reference)
§
Overall Width
MAX
8
8
0.86
0.97
4.67
4.90
.5.08
.122
2.90
3.00
3.10
.122
2.90
3.00
3.10
.022
.028
0.40
0.55
0.70
.037
.039
0.90
0.95
1.00
6
0
.006
.008
0.10
0.15
0.20
.012
.016
0.25
0.30
0.40
.034
0
0.15
6
7
7
7
7
*Controlling Parameter
§ Significant Characteristic
Notes:
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
/XX
Temperature
Range
Package
Device:
MCP1601: 500 mA Synchronous BUCK Regulator
MCP1601T: 500 mA Synchronous BUCK Regulator
Tape and Reel
Temperature Range:
I
Package:
MS = Plastic Micro Small Outline (MSOP), 8-lead
Examples:
a)
MCP1601-I/MS:
b)
MCP1601T-I/MS: Tape and Reel,
8LD MSOP package.
8LD MSOP package.
= -40°C to +85°C
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.
© 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® 8-bit MCUs, KEELOQ® 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
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Tel: 65-6334-8870 Fax: 65-6334-8850
Taiwan
Microchip Technology (Barbados) Inc.,
Taiwan Branch
11F-3, No. 207
Tung Hua North Road
Taipei, 105, Taiwan
Tel: 886-2-2717-7175 Fax: 886-2-2545-0139
EUROPE
Austria
Microchip Technology Austria GmbH
Durisolstrasse 2
A-4600 Wels
Austria
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark
Microchip Technology Nordic ApS
Regus Business Centre
Lautrup hoj 1-3
Ballerup DK-2750 Denmark
Tel: 45 4420 9895 Fax: 45 4420 9910
France
Microchip Technology SARL
Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79
Germany
Microchip Technology GmbH
Steinheilstrasse 10
D-85737 Ismaning, Germany
Tel: 49-89-627-144 0 Fax: 49-89-627-144-44
Italy
Microchip Technology SRL
Centro Direzionale Colleoni
Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy
Tel: 39-039-65791-1 Fax: 39-039-6899883
United Kingdom
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.