The MCP1603 is a high efficient, fully integrated
500 mA synchronous buck regulator whose 2.7V to
5.5V input voltage range makes it ideally suited for
applications powered from 1-cell Li-Ion or 2-cell/3-cell
NiMH/NiCd batteries.
At heavy loads, the MCP1603 operates in the 2.0 MHz
fixed frequency PWM mode which provides a low
noise, low output ripple, small-size solution. When the
load is reduced to light levels, the MCP1603
automatically changes operation to a PFM mode to
minimize quiescent current draw from the battery. No
intervention is necessary for a smooth transition from
one mode to another. These two modes of operation
allow the MCP1603 to achieve the highest efficiency
over the entire operating current range.
The MCP1603 is available with either an adjustable or
fixed output voltage. The available fixed output voltage
options are 1.2V, 1.5V, 1.8V, 2.5V, and 3.3V. When a
fixed option is used, only three additional small external
components are needed to form a complete solution.
Couple this with the low profile, small-foot print
packages and the entire system solution is achieved
with minimal size.
Additional protection features include: UVLO,
overtemperature, and overcurrent protection.
† 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 sections of this specification is not intended.
Exposure to maximum rating conditions for extended periods
may affect device reliability.
2: Reference Feedback Voltage Tolerance applies to adjustable output voltage setting.
is the output voltage setting.
3: V
R
4: The maximum allowable power dissipation is a function of ambient temperature, the maximum allowable
temperature and the thermal resistance from junction to air (i.e. T
allowable power dissipation causes the device to initiate thermal shutdown.
5: The internal MOSFET switches have an integral diode from the L
to the GND pin. In cases where these diodes are forward-biased, the package power dissipation limits
must be adhered to. Thermal protection is not able to limit the junction temperature for these cases.
6: The current limit threshold is a cycle-by-cycle peak current limit.
= 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
OUT
ParametersSymMinTypMaxUnitsConditions
Output Characteristics
Adjustable Output Voltage RangeV
Reference Feedback VoltageV
Reference Feedback Voltage
To le r an c e
Feedback Input Bias CurrentI
Output Voltage Tolerance FixedV
V
Line RegulationV
Load RegulationV
Internal Oscillator FrequencyF
Start Up TimeT
R
P-ChannelR
DSon
R
N-ChannelR
DSon
L
Pin Leakage CurrentI
X
Positive Current Limit Threshold+I
Note 1: The minimum V
has to meet two conditions: VIN ≥ 2.7V and VIN ≥ V
IN
LX(MAX)
OUT
FB
VFB
OUT
OUT
LINE-
REG
LOADREG
OSC
SS
DSon-P
DSon-N
LX
0.8—4.5VNote 2
—0.8—V
-3.0—+3.0%TA = -40°C to +25°C
-2.5—+2.5%T
—0.1—nA
-3.0%V
-2.5V
R
R
—0.3—%/VV
—0.35—%VIN=VR+1.5V,
1.52.02.8MHz
—0.6—msT
—500—mΩIP=100mA
—500—mΩIN= 100 mA
-1.0±0.11.0µASHDN =0V, VIN=5.5V,
—860—mANote 6
2: Reference Feedback Voltage Tolerance applies to adjustable output voltage setting.
3: V
is the output voltage setting.
R
4: The maximum allowable power dissipation is a function of ambient temperature, the maximum allowable
temperature and the thermal resistance from junction to air (i.e. T
allowable power dissipation causes the device to initiate thermal shutdown.
5: The internal MOSFET switches have an integral diode from the L
to the GND pin. In cases where these diodes are forward-biased, the package power dissipation limits
must be adhered to. Thermal protection is not able to limit the junction temperature for these cases.
6: The current limit threshold is a cycle-by-cycle peak current limit.
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.
Note: Unless otherwise indicated, VIN= SHDN =3.6V, C
T
= +25°C. Adjustable or fixed output voltage options can be used to generate the Typical Performance Characteristics.
path to remove heat from the device. Electrically this pad is at
ground potential and should be connected to GND
MCP1603
Description
3.1Power Supply Input Voltage Pin
)
(V
IN
Connect the input voltage source to VIN. The input
source must be decoupled to GND with a 4.7 µF
capacitor.
3.2Ground Pin (GND)
Ground pin for the device. The loop area of the ground
traces should be kept as minimal as possible.
3.3Shutdown Control Input Pin
(SHDN
The SHDN pin is a logic-level input used to enable or
disable the device. A logic high (> 45% of VIN) will
enable the regulator output. A logic-low (< 15% of VIN)
will ensure that the regulator is disabled.
)
3.4Feedback / Output Voltage Pin
(V
FB/VOUT
For adjustable output options, connect the center of the
output voltage divider to the VFB/V
output voltage options, connect the output directly to
the V
FB/VOUT
pin.
)
pin. For fixed-
OUT
3.5Switch Node, Buck Inductor
Connection Pin (L
Connect the LX pin directly to the buck inductor. This
pin carries large signal-level current; all connections
should be made as short as possible.
)
X
3.6Exposed Metal Pad (EP)
For the DFN package, connect the Exposed Pad to
GND, with vias into the GND plane. This connection to
the GND plane will aid in heat removal from the
package.
The MCP1603 is a synchronous buck regulator that
operates in a Pulse Frequency Modulation (PFM)
mode or a Pulse Width Modulation (PWM) mode to
maximize system efficiency over the entire operating
current range. Capable of operating from a 2.7V to
5.5V input voltage source, the MCP1603 can deliver
500 mA of continuous output current.
When using the MCP1603, the PCB area required for
a complete step-down converter is minimized since
both the main P-Channel MOSFET and the synchronous N-Channel MOSFET are integrated. Also while in
PWM mode, the device switches at a constant
frequency of 2.0 MHz (typ) which allow for small filtering components. Both fixed and adjustable output
voltage options are available. The fixed voltage options
(1.2V, 1.5V 1.8V, 2.5V, 3.3V) do not require an external
voltage divider which further reduces the required
circuit board footprint. The adjustable output voltage
options allow for more flexibility in the design, but
require an external voltage divider.
Additionally the device features undervoltage lockout
(UVLO), overtemperature shutdown, overcurrent
protection, and enable/disable control.
4.2Synchronous Buck Regulator
The MCP1603 has two distinct modes of operation that
allow the device to maintain a high level of efficiency
throughout the entire operating current and voltage
range. The device automatically switched between
PWM mode and PFM mode depending upon the output
load requirements.
4.2.1FIXED FREQUENCY, PWM MODE
During heavy load conditions, the MCP1603 operates
at a high, fixed switching frequency of 2.0 MHz (typical)
using current mode control. This minimizes output ripple (10 - 15 mV typically) and noise while maintaining
high efficiency (88% typical with V
V
= 1.8V, I
OUT
During normal PWM operation, the beginning of a
switching cycle occurs when the internal P-Channel
MOSFET is turned on. The ramping inductor current is
sensed and tied to one input of the internal high-speed
comparator. The other input to the high-speed comparator is the error amplifier output. This is the difference
between the internal 0.8V reference and the divideddown output voltage. When the sensed current
becomes equal to the amplified error signal, the highspeed comparator switches states and the P-Channel
MOSFET is turned off. The N-Channel MOSFET is
turned on until the internal oscillator sets an internal RS
latch initiating the beginning of another switching cycle.
PFM-to-PWM mode transition is initiated for any of the
following conditions:
• Continuous device switching
• Output voltage has dropped out of regulation
= 300 mA).
OUT
= 3.6V,
IN
4.2.2LIGHT LOAD, PFM MODE
During light load conditions, the MCP1603 operates in
a PFM mode. When the MCP1603 enters this mode, it
begins to skip pulses to minimize unnecessary quiescent current draw by reducing the number of switching
cycles per second. The typical quiescent current draw
for this device is 45 µA.
PWM-to-PFM mode transition is initiated for any of the
following conditions:
• Discontinuous inductor current is sensed for a set
duration
• Inductor peak current falls below the transition
threshold limit
The output of the MCP1603 is controlled during startup. This control allows for a very minimal amount of
overshoot during start-up from VIN rising above
V
OUT
the UVLO voltage or SHDN being enabled.
4.4Overtemperature Protection
Overtemperature protection circuitry is integrated in the
MCP1603. This circuitry monitors the device junction
temperature and shuts the device off, if the junction
temperature exceeds the typical 150°C threshold. If
this threshold is exceeded, the device will automatically
restart once the junction temperature drops by
approximately 10°C. The soft start is reset during an
overtemperture condition.
4.5Overcurrent Protection
Cycle-by-cycle current limiting is used to protect the
MCP1603 from being damaged when an external short
circuit is applied. The typical peak current limit is
860 mA. If the sensed current reaches the 860 mA
limit, the P-Channel MOSFET is turned off, even if the
output voltage is not in regulation. The device will
attempt to start a new switching cycle when the internal
oscillator sets the internal RS latch.
4.6Enable/Disable Control
The SHDN pin is used to enable or disable the
MCP1603. When the SHDN
device is disabled. When pulled high the device is
enabled and begins operation provided the input
voltage is not below the UVLO threshold or a fault
condition exists.
pin is pulled low, the
4.7Undervoltage Lockout (UVLO)
The UVLO feature uses a comparator to sense the
input voltage (V
than the voltage necessary to properly operate the
MCP1603, the UVLO feature will hold the converter off.
When V
UVLO is released and soft start begins. Hysteresis is
built into the UVLO circuit to compensate for input
impedance. For example, if there is any resistance
between the input voltage source and the device when
it is operating, there will be a voltage drop at the input
to the device equal to I
is 140 mV.
The MCP1603 500 mA synchronous buck regulator
operates over a wide input voltage range (2.7V to 5.5V)
and is ideal for single-cell Li-Ion battery powered
applications, USB powered applications, three cell
NiMH or NiCd applications and 3V or 5V regulated
input applications. The 5-lead TSOT and 8-lead 2x3
DFN packages provide a small footprint with minimal
external components.
5.2Fixed Output Voltage Applications
Typical Application Circuit shows a fixed MCP1603
in an application used to convert three NiMH batteries
into a well regulated 1.8V @ 500 mA output. A 4.7 µF
input capacitor, 4.7 µF output capacitor, and a 4.7 µH
inductor make up the entire external component solution for this application. No external voltage divider or
compensation is necessary. In addition to the fixed
1.8V option, the MCP1603 is also available in 1.2V,
1.5V, 2.5V, or 3.3V fixed voltage options.
5.3Adjustable Output Voltage
Applications
For adjustable output applications, an additional R-C
compensation network is necessary for control loop
stability. Recommended values for any output voltage
are:
R
COMP
C
COMP
Refer to Figure 6-2 for proper placement of R
C
COMP
=4.99kΩ
=33pF
.
COMP
and
5.4Input Capacitor Selection
The input current to a buck converter, when operating
in continuous conduction mode, is a squarewave with
a duty cycle defined by the output voltage (V
input voltage (V
undesirable input voltage transients, the input capacitor
should be a low ESR type with an RMS current rating
given by Equation 5.5. Because of their small size and
low ESR, ceramic capacitors are often used. Ceramic
material X5R or X7R are well suited since they have a
low temperature coefficient and acceptable ESR.
) relationship of V
IN
OUT/VIN
. To prevent
EQUATION 5-2:
OUT
) to
When the desired output for a particular application is
not covered by the fixed voltage options, an adjustable
MCP1603 can be used. The circuit listed in Figure 6-2
shows an adjustable MCP1603 being used to convert a
5V rail to 1.0V @ 500 mA. The output voltage is adjustable by using two external resistors as a voltage
divider. For adjustable-output voltages, it is
recommended that the top resistor divider value be
200 kΩ. The bottom resistor value can be calculated
using the following equation:
EQUATION 5-1:
Table 5-1 contains the recommend range for the input
capacitor value.
5.5Output Capacitor Selection
The output capacitor helps provide a stable output
voltage during sudden load transients, smooths the
current that flows from the inductor to the load, and
reduces the output voltage ripple. Therefore, low ESR
capacitors are a desirable choice for the output capacitor. As with the input capacitor, X5R and X7R ceramic
capacitors are well suited for this application.
The output ripple voltage is often a design specification. A buck converters’ output ripple voltage is a
function of the charging and discharging of the output
capacitor and the ESR of the capacitor. This ripple
voltage can be calculated by Equation 5-3.
Table 5-1 contains the recommend range for the output
capacitor value.
TABLE 5-1:CAPACITOR VALUE RANGE
C
IN
Minimum4.7 µF4.7 µF
Maximum—22 µF
C
OUT
5.6Inductor Selection
When using the MCP1603, the inductance value can
range from 3.3 µH to 10 µH. An inductance value of
4.7 µH is recommended to achieve a good balance
between converter load transient response and minimized noise.
The value of inductance is selected to achieve a
desired amount of ripple current. It is reasonable to
assume a ripple current that is 20% of the maximum
load current. The larger the amount of ripple current
allowed, the larger the output capacitor value becomes
to meet ripple voltage specifications. The inductor
ripple current can be calculated according to the following equation.
When considering inductor ratings, the maximum DC
current rating of the inductor should be at least equal to
the maximum load current, plus one half the peak-topeak inductor ripple current (1/2 * ΔI
resistance adds to the total converter power loss. An
inductor with a low DC resistance allows for higher
converter efficiency.
). The inductor DC
L
5.7Thermal Calculations
The MCP1603 is available in two different packages
(TSOT-23 and 2x3 DFN). By calculating the power
dissipation and applying the package thermal
resistance, (θ
estimated. The maximum continuous junction
temperature rating for the MCP1603 is +125°C.
To quickly estimate the internal power dissipation for
the switching buck regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency, the internal power dissipation is
estimated by:
EQUATION 5-5:
The difference between the first term, input power
dissipation, and the second term, power delivered, is
the internal power dissipation. This is an estimate
assuming that most of the power lost is internal to the
MCP1603. There is some percentage of power lost in
the buck inductor, with very little loss in the input and
output capacitors.
Good printed circuit board layout techniques are
important to any switching circuitry and switching
power supplies are no different. When wiring the high
current paths, short and wide traces should be used.
This high current path is shown with red connections in
Figure 5-1. The current in this path is switching.
FIGURE 5-1:PCB High Current Path.
Therefore, it is important that the components along the
high current path should be placed as close as possible
to the MCP1603 to minimize the loop area.
The feedback resistors and feedback signal should be
routed away from the switching node and this switching
current loop. When possible ground planes and traces
should be used to help shield the feedback signal and
minimize noise and magnetic interference.
YYear code (last digit of calendar year)
YYYear code (last 2 digits of calendar year)
WWWeek code (week of January 1 is week ‘01’)
NNNAlphanumeric traceability code
Pb-free JEDEC designator for Matte Tin (Sn)
*This package is Pb-free. The Pb-free JEDEC designator ()
can be found on the outer packaging for this package.
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.
8-Lead Plastic Dual Flat, No Lead Package (MC) – 2x3x0.9 mm Body [DFN]
Notes:
1. Pin 1 visual index feature may vary, but must be located within the hatched area.
2. Package may have one or more exposed tie bars at ends.
3. Package is saw singulated.
4. Dimensioning and tolerancing per ASME Y14.5M.
BSC: Basic Dimension. Theoretically exact value shown without tolerances.
REF: Reference Dimension, usually without tolerance, for information purposes only.
Note:For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
UnitsMILLIMETERS
Dimension LimitsMINNOMMAX
Number of PinsN8
Pitche0.50 BSC
Overall HeightA0.800.901. 00
Standoff A10.000.020.05
Contact ThicknessA30.20 REF
Overall LengthD2.00 BSC
Overall WidthE3.00 BSC
Exposed Pad LengthD21.30–1.75
Exposed Pad WidthE21.50–1.90
Contact Widthb0.180.250.30
Contact LengthL0.300.400.50
Contact-to-Exposed PadK0.20––
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