Microchip MCP1612T-ADJIMS Single 1a, 1.4 mhz synchronous buck regulator Datasheet

MCP1612
Single 1A, 1.4 MHz Synchronous Buck Regulator
Features
Description
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The MCP1612 is a 1A, 1.4 MHz, fully-integrated,
current mode-controlled, synchronous buck regulator.
The MCP1612 is packaged in the 8-pin MSOP and
space-saving, 3x3 DFN packages. The DFN package
also provides a lower thermal resistance package
option for high-power, high ambient temperature
applications. With an input operating range from 2.7V
to 5.5V, the MCP1612 is ideal for applications that are
powered by one single-cell Li-Ion, 2- to 3-cell NiMH,
NiCd or alkaline sources.
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Fixed Switching Frequency: 1.4 MHz
Input Operating Voltage Range: 2.7V to 5.5V
Integrated Buck and Synchronous Switches
Adjustable-Output Voltage Range: 0.8V to 5.0V
100% Duty Cycle Capable for Low Input Voltage
Continuous Output Current Capability: 1A
Shutdown Control with IQ < 0.01 µ A (Typ.)
Integrated Soft-Start Feature
Integrated Undervoltage Lockout (UVLO)
Protection
Integrated Overtemperature Protection
Fast Dynamic Response to Line and Load Steps
Small, 8-Pin DFN and MSOP Packages
Operating Temperature Range: -40°C to +85°C
Applications
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Network Interface Cards
Portable Computers
Set-Top Boxes
DSL Modems and Routers
USB-Powered Devices
GBIC Modules
High-Speed Data System Bus Termination
Medical Instruments
Cellular/GSM/PHS Phones
+5V or +3.3V Distributed Voltages
The output voltage of the MCP1612 is easily set over
the range of 0.8V to 5.0V by using an external resistor
divider. The external inductor and output capacitor size
are minimized due to an internally-fixed, 1.4 MHz clock
being used to set the switching frequency. The fixed
clock allows for continuous, fixed-frequency PWM
operation over the full load range.
The MCP1612 is designed to provide fast dynamic
response to sudden changes in input voltage and load
current to minimize the necessary amount of external
output capacitance.
The MCP1612 can be used with ceramic, tantalum or
aluminum electrolytic output capacitors. Ceramic
capacitors with values as low as 4.7 µF can be used to
keep the output ripple voltage low. For applications that
require better load step performance, the value of the
output capacitor can be increased to 47 µF.
Additional features integrated into the MCP1612
include shutdown capability, soft-start, UVLO,
overcurrent and overtemperature protection.
Package Types
8-Lead DFN
VIN 1
VCC 2
© 2005 Microchip Technology Inc.
8 LX
8-Lead MSOP
VIN 1
8 LX
7 PGND
VCC 2
SHDN 3
6 AGND
SHDN 3
6 AGND
COMP 4
5 FB
COMP 4
5 FB
7 PGND
DS21921B-page 1
MCP1612
Functional Block Diagram
VCC
Undervoltage
Lockout
(UVLO)
UVLO
VIN
ISENSE P-Channel
Slope Comp.
+
+
Peak Current
Limit
Comp
VREF
FB
–
gm
+
Disable
PDRV
Disable
INSET
Circuit
LX
NDRV
IN
SoftStart
Disable
VREF
Peak Current
Limit
1.4 MHz Clock
PGND
LeadingEdge
Blank
PGND
VCC
VCC
UVLO
1.2V
A
VBG
SHDN
Disable
AGND
0.8V
Thermal
Shutdown
AGND
AGND
DS21921B-page 2
© 2005 Microchip Technology Inc.
MCP1612
Typical Application Circuit
MCP1612 3.3V to 1.2V Synchronous Buck Converter
3.3 VIN ±10%
CIN
10 µF
Ceramic
ON
1
VIN
Lx
8 L = 3.3 µH
MCP1612
10Ω
2
CBYP
0.1 µF
Ceramic
3
VCC
PGND
SHDN
AGND
7
1.2V VOUT @ 1A
COUT
10 µF
Ceramic
100 kΩ
6
200 kΩ
OFF
4
Comp
FB
5
25 kΩ
1000 pF
© 2005 Microchip Technology Inc.
DS21921B-page 3
MCP1612
1.0
ELECTRICAL
CHARACTERISTICS
† 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.
Absolute Maximum Ratings †
VIN – AGND .......................................................................6.0V
(SHDN, FB, VCC, Comp ........... (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 (HBM) ....................................... 4 kV
ESD protection on all pins (MM)......................................... 300V
DC CHARACTERISTICS
Electrical Specifications: Unless otherwise noted, VIN = VCC = VSHDN = 3.3V, VOUT = 1.8V, CIN = COUT = 10 µF, L = 3.3 µH,
ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
Conditions
Input Voltage
Input Operating Voltage
VIN
2.7
—
5.5
V
Input Shutdown Current
I(VIN)
—
0.01
1
µA
Shutdown mode (SHDN = GND)
Input Quiescent Current
I(VIN)
—
5
7
mA
ILOAD = 0 mA
FOSC
1.2
1.4
1.6
MHz
RDSon P-Channel
RDSon-P
—
300
—
mΩ
IP = 250 mA
RDSon N-Channel
RDSon-N
—
300
—
mΩ
IN = 250 mA
ILX
-1
—
1
µA
SHDN = 0V, VIN = 5.5V, LX = 0V,
LX = 5.5V
Positive Current Limit Threshold
+ILX(MAX)
—
2.3
—
A
Negative Current Limit Threshold
-ILX(MAX)
—
-1.4
—
A
gm
35
62
90
µA/V
Oscillator Characteristics
Internal Oscillator Frequency
Internal Power Swicthes
LX Pin Leakage Current
Feedback Characteristics
Transconductance from FB to
COMP
Output Voltage
Output Voltage Range
Reference Feedback Voltage
Feedback Input Bias Current
VOUT
0.8
—
VIN
V
VFB
0.78
0.8
0.82
V
IVFB
—
1
—
nA
Line Regulation
VLINE-REG
—
0.15
0.5
%/V
Load Regulation
VLOAD-REG
—
0.25
—
%
Note 1:
2:
VIN = 2.7V to 5.5V, ILOAD = 100 mA
VIN = 4.2V, ILOAD = 100 mA to 1A
The integrated MOSFET switches have an integral diode from the LX pin to VIN and from LX to PGND. In cases where
these diodes are forward-biased, the package power dissipation limits must be adhered to. Thermal protection is not
able to regulate the junction temperature for these cases.
UVLO is specified for a falling VIN. Once the UVLO is activated, the UVLO-HYS must be overcome before the device will
return to operation.
DS21921B-page 4
© 2005 Microchip Technology Inc.
MCP1612
DC CHARACTERISTICS (CONTINUED)
Electrical Specifications: Unless otherwise noted, VIN = VCC = VSHDN = 3.3V, VOUT = 1.8V, CIN = COUT = 10 µF, L = 3.3 µH,
ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Parameters
Sym
Min
Typ
Max
Units
UVLO
2.4
2.55
2.7
V
UVLO-HYS
—
200
—
mV
TSHD
—
160
—
°C
TSHD-HYS
—
9
—
°C
Logic-High Input
VIN-HIGH
45
—
—
% of VIN
Logic-Low Input
VIN-LOW
—
—
15
% of VIN
Conditions
Protection Features
Undervoltage Lockout
Undervoltage Lockout Hysteresis
Thermal Shutdown
Thermal Shutdown Hysteresis
Note 2
Note 1
Interface Signal (SHDN)
Note 1:
2:
The integrated MOSFET switches have an integral diode from the LX pin to VIN and from LX to PGND. In cases where
these diodes are forward-biased, the package power dissipation limits must be adhered to. Thermal protection is not
able to regulate the junction temperature for these cases.
UVLO is specified for a falling VIN. Once the UVLO is activated, the UVLO-HYS must be overcome before the device will
return to operation.
TEMPERATURE SPECIFICATIONS
Electrical Specifications: VIN = 3.0V to 5.5V, FOSC = 1 MHz with 10% Duty Cycle, CIN = 0.1 µF. TA = -40°C to +125°C.
Parameters
Sym
Min
Typ
Max
Units
Conditions
TA
-65
—
+150
°C
Continuous
Temperature Ranges
Storage Temperature Range
Maximum Junction Temperature
TJ
—
—
+150
°C
Transient Only
Operating Junction Temperature Range
TA
- 40
—
+ 125
°C
Continuous Operation
Thermal Resistance, 8L-MSOP
θJA
—
208
—
°C/W
Typical 4-layer board interconnecting
vias
Thermal Resistance, 8L-DFN
θJA
—
41
—
°C/W
Typical 4-layer board interconnecting
vias
Thermal Package Resistances
© 2005 Microchip Technology Inc.
DS21921B-page 5
MCP1612
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
90
80
70
60
50
40
30
20
10
0
0.50
VOUT = 2.5V
Dropout Voltage (V)
Efficiency (%)
Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA,
TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.7V
0.40
0.30
VOUT = 3.3V
0.20
0.10
VIN = 3.3V
0.00
10
100
1000
0
200
Load Current (mA)
100
90
80
70
60
50
40
30
20
10
0
Efficiency vs. Load Current,
Efficiency (%)
VOUT = 3.3V
VOUT = 2.5V
VIN = 5.0V
10
100
FIGURE 2-4:
Load Current.
Input Quiescent Current (mA)
FIGURE 2-1:
VIN = 3.3V.
6.0
5.5
TA = +85oC
5.0
o
4.5
TA = +25 C
4.0
o
TA = -40 C
VOUT = 1.8V
3.5
3
VOUT = 1.2V VIN = 3.3V
-0.4
VOUT = 1.8V, VIN = 3.3V
-0.8
-1
-1.2
VOUT = 3.3V, VIN = 5.0V
-1.4
FIGURE 2-5:
Input Voltage.
Oscillator Frequency (MHz)
Change In Output Voltage (mV)
1000
3.5
4
4.5
5
5.5
Input Voltage (V)
0
-0.6
800
6.5
2.5
1000
Efficiency vs. Load Current,
-0.2
600
Dropout Voltage vs.
Load Current (mA)
FIGURE 2-2:
VIN = 5.0V.
400
Load Current (mA)
Input Quiescent Current vs.
1.42
TA = -40oC
1.41
1.40
TA = +25oC
1.39
1.38
1.37
TA = +85oC
1.36
0
200
400
600
800
1000
2.5
Load Current (mA)
FIGURE 2-3:
Load Current.
DS21921B-page 6
Output Voltage vs.
3
3.5
4
4.5
5
5.5
Input Voltage (V)
FIGURE 2-6:
Input Voltage.
Oscillator Frequency vs.
© 2005 Microchip Technology Inc.
MCP1612
TYPICAL PERFORMANCE CURVES (Continued)
Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA,
TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
Start-up from VIN = 0V to 3.3V
IOUT = 100 mA to 800 mA
VIN = 5.0V
VOUT = 3.3V
VOUT
100 mV/DIV
VIN
2.0V/DIV
IOUT
500 mA/DIV
VOUT
1.0V/DIV
VOUT = 1.8V
1.0 ms/DIV
FIGURE 2-7:
500 µs/DIV
Power-Up from VIN.
FIGURE 2-10:
Load Transient Response.
Line Step Response, VIN = 3.0V to 4.0V
Start-up from SHDN
VIN
2.0V/DIV
SHDN
2.0V/DIV
VOUT
50 mV/DIV
VOUT
1.0V/DIV
VOUT = 1.8V
IOUT = 800 mA
VOUT = 1.8V
1.0 ms/DIV
FIGURE 2-8:
200 µs/DIV
Power-Up from Shutdown.
FIGURE 2-11:
Line Step Response, VIN = 4.5V to 5.5V
IOUT = 100 mA to 800 mA
VIN
2.0V/DIV
VOUT
200 mV/DIV
VOUT
50 mV/DIV
IOUT
500 mA/DIV
VOUT = 3.3V
IOUT = 800 mA
VOUT = 1.8V
50 µs/DIV
FIGURE 2-9:
Line Transient Response.
Load Transient Response.
© 2005 Microchip Technology Inc.
200 µs/DIV
FIGURE 2-12:
Line Transient Response.
DS21921B-page 7
MCP1612
TYPICAL PERFORMANCE CURVES (Continued)
Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA,
TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C.
IOUT = 10 mA, VOUT = 1.8V
IOUT = 1A, VOUT = 1.8V
LX
5.0V/DIV
LX
2.0V/DIV
VOUT
10 mV/DIV
VOUT
10 mV/DIV
IIND
500 mA/DIV
IIND
100 mA/DIV
VIN = 3.3V
VIN = 3.3V
500 ns/DIV
FIGURE 2-13:
Waveform.
DS21921B-page 8
Low Load Current Switching
500 ns/DIV
FIGURE 2-14:
Waveform.
High Load Current Switching
© 2005 Microchip Technology Inc.
MCP1612
3.0
MCP1612 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1:
Pin No.
3.1
PIN FUNCTION TABLE
Name
Function
1
VIN
Input Voltage Pin
2
VCC
Analog Input Voltage Pin
3
SHDN
Shutdown Control Input Pin
4
COMP
Transconductance Amplifier Output Pin
5
FB
Feedback Input Pin
6
AGND
Analog Ground Pin
7
PGND
Power Ground Pin
8
LX
Buck Inductor Output Pin
Input Voltage Pin (VIN)
3.5
Feedback Pin (FB)
Connect the input voltage source to VIN. For normal
operation, the voltage on VIN should be between +2.7V
and +5.5V. A 10 µF bypass capacitor should be
connected between VIN and PGND.
Connect the output voltage of the buck converter
through an external resistor divider to FB to regulate
the output voltage. The nominal voltage compared to
this input for pulse termination is 0.8V.
3.2
3.6
Analog Input Voltage Pin (VCC)
VCC provides bias for internal analog functions. This
voltage is derived by filtering the VIN supply.
3.3
Tie all small-signal ground returns to AGND. Noise on
AGND can effect the sensitive internal analog
measurements.
Shutdown Input Pin (SHDN)
Connect SHDN to a logic-level input in order to turn the
regulator on or off. A logic-high (>45% of VIN) will
enable the regulator. A logic-low (<15% of VIN) will
force the regulator into Shutdown mode. When in
shutdown, both the P-channel and N-channel switches
are turned off.
3.7
Compensation Pin (COMP)
COMP is the internal transconductance amplifier
output pin. External compensation is connected to
COMP for control-loop stabilization.
© 2005 Microchip Technology Inc.
Power Ground Pin (PGND)
Connect all large-signal ground returns to PGND. These
large-signal traces should have a small loop area and
length to prevent coupling of switching noise to
sensitive traces.
3.8
3.4
Analog Ground Pin (AGND)
Buck Inductor Output Pin (LX)
Connect LX directly to the buck inductor. This pin
carries large signal-level currents; all connections
should be made as short as possible.
DS21921B-page 9
MCP1612
4.0
DETAILED DESCRIPTION
4.1
Device Overview
The MCP1612 is a 1A synchronous buck converter
switching at 1.4 MHz to minimize external component
size and cost. While utilizing a fixed-frequency Current
mode architecture, the MCP1612 provides fast
response to sudden load changes, as well as
overcurrent protection in the event of a shorted load.
The input voltage range is 2.7V to 5.5V, while the
output voltage is adjustable by properly setting an
external resistor divider and can range from 0.8V to
VIN. Integrated soft-start, UVLO and overtemperature
protection minimize external circuitry and component
count.
4.2
Current Mode Control Scheme
The MCP1612 incorporates a Peak Current mode
control scheme. Peak Current mode is used to obtain
high gain in the PWM control loop for very fast
response to dynamic line and load conditions. With
both the P-channel and N-channel MOSFETs turned
off, the beginning of a cycle occurs on the negative
edge of the internal 1.4 MHz oscillator, the P-channel
MOSFET turns on and current ramps up into the buck
inductor. The inductor current is sensed and tied to one
input of a high-speed comparator. The other input of
the high-speed comparator is the error amplifier output.
This is the amplified difference between the internal
0.8V reference and the divided-down VOUT signal at
the FB pin of the MCP1612. When the sensed inductor
current ramps up to the point that is equal to the
amplified error signal, the high-speed comparator
output switches states and the P-channel MOSFET is
turned off until the beginning of the next clock cycle and
the N-channel is turned on. The width of the pulse (or
duty cycle) is ideally determined by the VOUT/VIN ratio
of the DC/DC converter. The actual duty cycle is slightly
larger to account for the non-ideal losses of the
integrated MOSFET switches and the losses in the
external inductor.
4.3
Low-Dropout Operation
The MCP1612 is capable of operating over a wide
range of input voltages. The PWM architecture allows
for the P-channel MOSFET to achieve 100% duty cycle
operation for applications that have minimal input voltage headroom. During 100% Duty Cycle mode, the
output voltage (VOUT) is equal to the Output Current
(IOUT) x Resistance (P-channel RDSON + RINDUCTOR).
4.4
Current Limit
Cycle-by-cycle current limit is used to protect the
MCP1612 from being damaged when an external short
circuit is applied. The typical peak current limit is 2.3A.
If the sensed inductor current reaches the 2.3A limit,
the P-channel MOSFET is turned off, even if the output
voltage is not in regulation.
4.5
Soft-Start
During normal power-up, as VIN rises above the UVLO
protection setting (or, in the case of a logic-low to logichigh transition on the shutdown pin), the rise time of the
MCP1612 output voltage is controlled by the soft-start
feature. This is accomplished by allowing the output of
the error amplifier to slowly rise. This feature prevents
the output voltage from overshooting the desired value
and the sudden inrush of current, depleting the input
capacitors and causing a large dip in input voltage. This
large dip in the input voltage can trip the UVLO threshold, causing the converter to shut down prior to reaching steady-state operation.
4.6
Undervoltage Lockout (UVLO)
The UVLO feature uses a comparator to sense the
input voltage level (VIN). If the input voltage is lower
than the voltage necessary to properly operate the
MCP1612, the UVLO feature will hold the converter off.
When VIN rises above the necessary input voltage, the
UVLO is released and soft-start begins. For the
MCP1612, the UVLO protection threshold is at a
maximum of 2.7V. 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 converter (once it starts), there
will be a voltage drop at the converter input equal to
IIN x RIN. The typical hysteresis for the MCP1612 is
200 mV.
4.7
Overtemperature Protection
The MCP1612 has an integrated overtemperature
protection circuit that monitors the device junction
temperature and shuts the device off if the junction
temperature exceeds the typical 160°C threshold. If the
overtemperature threshold is reached, the soft-start is
reset so that, when the junction temperature cools to
approximately 151°C, the device will automatically
restart and the output voltage will not overshoot.
4.8
Shutdown Input Operation
The SHDN pin is used to turn the MCP1612 on and off.
When the SHDN pin is tied low, the MCP1612 is off.
When tied high, the MCP1612 will be enabled and
begin operation as long as the input voltage is not
below the UVLO threshold.
DS21921B-page 10
© 2005 Microchip Technology Inc.
MCP1612
5.0
APPLICATION CIRCUITS/INFORMATION
MCP1612 3.3V to 1.2V Synchronous Buck Converter
3.3VIN ±10%
CIN
10 µF
Ceramic
ON
1
VIN
8 L = 3.3 µH
Lx
COUT
10 µF
Ceramic
MCP1612
10Ω
2
CBYP
0.1 µF
Ceramic
3
VCC
PGND
SHDN
AGND
1.2V VOUT @ 1A
7
100 kΩ
6
200 kΩ
OFF
4
Comp
5
FB
25 kΩ
1000 pF
FIGURE 5-1:
5.1
Typical Application Circuit.
Typical Applications
The MCP1612 buck controller can be used in several
different applications where a voltage that is lower than
the supply voltage is required. Its small size, low cost
and high efficiency make the MCP1612 a good choice
for densely-packaged applications. The input voltage
range, low-dropout voltage and low shutdown current
make this part perfectly suited for battery-powered
applications.
5.2
Design Example
The step-by-step design of a buck converter with the
following parameters is presented to illustrate how
easy the MCP1612 is to use.
Input voltage = 3.3V
Output voltage = 1.2V
Output current = 0A to 1A
Switching frequency = 1.4 MHz
5.2.1
SETTING OUTPUT VOLTAGE
The output voltage of the MCP1612 is set by using an
external resistor-divider network. The voltage present
at FB is internally compared to a 0.8V reference
voltage. A 200 kΩ resistor is recommended for R2, the
lower-end of the voltage divider. Using higher-value
© 2005 Microchip Technology Inc.
resistors will make the circuit more susceptible to noise
on the FB pin. Lower-value resistors can be used, if
necessary.
Equation 5-1, used to calculate the output voltage, is
shown below.
EQUATION 5-1:
V OUT
R1 = R 2 × ⎛ ------------- – 1⎞
⎝ V FB
⎠
Where:
VOUT = desired output voltage
VFB = MCP1612 internal reference
voltage
R1 = top resistor value
R2 = bottom resistor value
For this example:
VOUT = 1.2V
VFB = 0.8V
R2 = 200 kΩ
R1 = 100 kΩ
The MCP1612 is capable of a 15% duty cycle.
Instability may result when the duty cycle is below 15%.
If less than 15% duty cycle operation is needed, care
must be taken to ensure stable operation.
DS21921B-page 11
MCP1612
5.2.2
BUCK INDUCTOR
There are many requirements that need to be satisfied
when selecting the buck inductor. The application,
physical size, current rating, resistance, mounting
method, supplier, temperature range, minimum
inductance and cost all need to be considered.
Many suppliers specify the maximum peak current that
an inductor can handle before magnetic saturation
occurs. The peak current is equal to the maximum DC
output current, plus one-half the peak-to-peak AC
ripple current.
The value of the buck inductor is chosen to be 3.3 µH.
The AC ripple current is controlled by the size of the
buck inductor. The value of the inductor will therefore
need to be raised so that the converter operates in
Continuous Conduction mode. Calculation of the buck
inductor current rating follows.
VIN = 3.3V
VOUT = 1.2V
FSW = 1.4 MHz
IOUT(MAX) = 1A
TON = (1.2V/3.3V) x (1/1.4 MHz)
When the P-channel MOSFET is on, the current in the
buck inductor is ramped up. The voltage across the
inductor, the inductance and the MOSFET on-time are
required to determine the peak-to-peak ripple current.
When operating in Continuous Current mode, the ontime of the P-channel MOSFET is determined by
multiplying the duty cycle by the switching period. The
following equation can be used to determine the duty
cycle.
EQUATION 5-2:
V OUT
DutyCycle = ------------V IN
TON = 260 ns
VL = (3.3V – 1.2V) = 2.1V
ΔIL = (2.1V/3.3 µH) x 260 ns
ΔIL = 165 mA
IL(PEAK) = IOUT(MAX) + 1/2 ΔIL
IL(PEAK) = 1A + (165 mA)/2
IL(PEAK) = 1.08A
The inductor selected must have an inductance of
3.3 µH at a peak current rating of 1.08A. The DC resistance of the inductor should be as low as is feasibly
possible. Extremely low DC resistance inductors are
available, though a trade-off between size and cost
should be considered.
The on-time is then defined as follows.
5.2.3
EQUATION 5-3:
T ON
1
= DutyCycle × ---------F SW
Where:
FSW = switching frequency
The AC ripple current in the inductor can be calculated
by the following relationship.
EQUATION 5-4:
ΔI L
V L = L × -------Δt
Solving for ΔIL yields:
OUTPUT CAPACITOR
The output capacitor is used to filter the inductor AC
ripple current and provide storage for load transients.
The size and Equivalent Series Resistance (ESR) of
the output capacitor determines the amount of ripple
voltage present at the output of the converter. When
selecting the output capacitor, a design trade-off has to
be made between the acceptable ripple voltage and the
size/cost of the output capacitor. Ceramic capacitors
have very low ESR, but increase in cost with higher
values. Tantalum and electrolytic capacitors are
relatively inexpensive in higher values, but they also
have a much higher ESR.
The amount of capacitance needed to obtain the
desired ripple voltage is calculated by using the
following relationship.
EQUATION 5-6:
EQUATION 5-5:
VL
ΔI L = ------ × Δt
L
ΔV C
I C = C × ----------Δt
Where:
VL = voltage across the inductor
(VIN – VOUT)
Δt = on-time of the P-channel MOSFET
DS21921B-page 12
© 2005 Microchip Technology Inc.
MCP1612
5.2.6
Solving for C:
Δt
C = I C × ----------ΔV C
Where:
IC = peak-to-peak ripple current
Δt = on-time of P-channel MOSFET
ΔVC = output ripple voltage
There will also be some ripple voltage caused by the
ESR of the capacitor. The ripple is defined as follows.
EQUATION 5-7:
COMPENSATION COMPONENTS
An internal transconductance error amplifier is used to
compensate the buck converter. An external resistor
(RC) and capacitor (CC), connected between COMP
and GND, are all that is needed to provide a highbandwidth loop.
Table 5-1 identifies values for RC and CC for standard
buck inductor (L) and output capacitor (COUT) values.
TABLE 5-1:
RC and CC VALUES
L
COUT
RC
CC
3.3 µH
10.0 µF
25 kΩ
1000 pF
2.2 µH
4.7 µF
10 kΩ
1000 pF
V ESRRIPPLE = ESR × IC
5.3
For this example:
IC = 165 mA
C = 4.7 µF
Δt = 260 ns
ESR = 8 mΩ
ΔVC = (260 ns x 165 mA)/4.7 µF
ΔVC = 9.13 mV
VESRRIPPLE = 8 mΩ x 165 mA
VESRRIPPLE = 1.32 mV
ΔVOUT = ΔVC + VESRRIPPLE
ΔVOUT = 9.13 mV + 1.32 mV
ΔVOUT = 10.45 mV
5.2.4
INPUT CAPACITOR
Printed Circuit Board (PCB)
Layout
The MCP1612 is capable of switching over 1A at
1.4 MHz. As with all high-frequency switching power
supplies, good PCB layout techniques are essential to
prevent noise generated by the switching power-train
from interfering with the sensing circuitry.
There are two ground pins (PGND and AGND) on the
MCP1612 to separate the large-signal ground current
from the small-signal circuit ground. These two
grounds should be kept separate, only connecting near
the input bulk capacitor.
Care must also be taken to minimize the length and
loop area of the large signal connections. Components
connected to this loop consist of the input bulk
capacitor, VIN, PGND and LX pins of the MCP1612, the
buck inductor and the output filter capacitor.
For the buck topology, the input current is pulled from
the source and the input capacitor in pulses. The size
of the input capacitor will determine the amount of
current pulled from the source. For most applications,
a 10 µF ceramic capacitor connected between the
MCP1612’s VIN and PGND is recommended to filter the
current pulses. Less capacitance can be used for
applications that have low source impedance. The
ripple current rating for ceramic capacitors are typically
very high due to their low loss characteristics. Low-cost
electrolytic capacitors can be used, but their ripple
current rating should not be exceeded.
5.2.5
VCC INPUT
The VCC input is used to bias the internal MCP1612
circuitry. A 10Ω resistor is recommended between the
unregulated inputs VIN and VCC, along with a 0.1 µF
capacitor to ground to help isolate the VCC pin from the
switching noise.
© 2005 Microchip Technology Inc.
DS21921B-page 13
MCP1612
6.0
PACKAGING INFORMATION
6.1
Package Marking Information
8-Lead DFN (3mm x 3mm)
XXXX
YYWW
NNN
8-Lead MSOP
XXXXX
YWWNNN
Legend: XX...X
Y
YY
WW
NNN
e3
*
Note:
DS21921B-page 14
Example:
1612
I0532
256
Example:
1612I
532256
Customer-specific information
Year code (last digit of calendar year)
Year code (last 2 digits of calendar year)
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
Pb-free JEDEC designator for Matte Tin (Sn)
This package is Pb-free. The Pb-free JEDEC designator ( e3 )
can be found on the outer packaging for this package.
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.
© 2005 Microchip Technology Inc.
MCP1612
8-Lead Plastic Dual-Flat, No-Lead Package (MF) 3x3x0.9 mm Body (DFN) – Saw Singulated
D
p
b
n
L
EXPOSED
METAL
PAD
(NOTE 2)
E
PIN 1
ID INDEX
AREA
(NOTE 1)
E2
2
1
D2
TOP VIEW
BOTTOM VIEW
ALTERNATE EXPOSED
PAD CONFIGURATIONS
A1
A
EXPOSED
TIE BAR
(NOTE 3)
A3
INCHES
Units
Dimension Limits
MIN
MILLIMETERS*
NOM
MAX
MIN
NOM
MAX
Pitch
n
p
Overall Height
A
.031
.035
.039
0.80
0.90
1.00
Standoff
A1
.000
.001
.002
0.00
0.02
0.05
Contact Thickness
A3
Number of Pins
Overall Length
Exposed Pad Width
Overall Width
8
.026 BSC
0.65 BSC
.008 REF.
E
E2
8
0.20 REF.
.118 BSC
.043
D
.061
3.00 BSC
.063
1.09
.118 BSC
1.55
1.60
3.00 BSC
D2
.059
.092
.096
1.50
2.37
2.45
Contact Width
b
.009
.012
.015
0.23
0.30
0.37
Contact Length
L
.008
.016
.020
0.20
0.40
0.50
Exposed Pad Length
* Controlling Parameter
Notes:
1. Pin 1 visual index feature may vary, but must be located within the hatched area.
2. Exposed pad varies according to die attach paddle size.
3. Package may have one or more exposed tie bars at ends.
BSC: Basic Dimension. Theoretically exact value shown without tolerances.
See ASME Y14.5M
REF: Reference Dimension, usually without tolerance, for information purposes only.
See ASME Y14.5M
JEDEC equivalent: M0-229
Drawing No. C04-062
© 2005 Microchip Technology Inc.
Revised 07-20-05
DS21921B-page 15
MCP1612
8-Lead Plastic Micro Small Outline Package (MS) (MSOP)
E
E1
p
D
2
B
n
1
α
c
φ
L
F
A2
A
A1
β
Units
MILLIMETERS*
INCHES
NOM
MIN
Dimension Limits
MIN
MAX
NOM
MAX
Number of Pins
n
Pitch
p
Overall Height
A
-
-
.043
-
-
1.10
Molded Package Thickness
A2
.030
.033
.037
0.75
0.85
0.95
Standoff
A1
.000
-
.006
0.00
-
0.15
Overall Width
E
.193 BSC
4.90 BSC
Molded Package Width
E1
.118 BSC
3.00 BSC
Overall Length
D
.118 BSC
Foot Length
L
0.60
0.80
Footprint (Reference)
Foot Angle
F
φ
Lead Thickness
c
.003
.006
.009
0.08
-
0.23
Lead Width
B
α
.009
.012
.016
0.22
-
0.40
Mold Draft Angle Top
Mold Draft Angle Bottom
β
8
8
.026 BSC
.016
0.65 BSC
3.00 BSC
.024
.031
0.40
.037 REF
0°
0.95 REF
-
8°
0°
8°
-
5°
-
15°
5°
-
15°
5°
-
15°
5°
-
15°
* Controlling Parameter
Notes:
Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed .010" (0.254mm) per side.
BSC: Basic Dimension. Theoretically exact value shown without tolerances.
See ASME Y14.5M
REF: Reference Dimension, usually without tolerance, for information purposes only.
See ASME Y14.5M
JEDEC Equivalent: MO-187
Drawing No. C04-111
DS21921B-page 16
Revised 07-21-05
© 2005 Microchip Technology Inc.
MCP1612
APPENDIX A:
REVISION HISTORY
Revision B (September 2005)
The following is the list of modifications:
1.
2.
3.
4.
5.
Changed pin 6 in Package Types diagram on
front page.
Removed device qualification note in Package
Marking section.
Removed device qualification note in Package
Outline drawing.
Removed device qualification note in Package
Identification System section
Replaced MSOP and QFN package diagrams.
Revision A (December 2004)
• Original Release of this Document.
© 2005 Microchip Technology Inc.
DS21921B-page 17
MCP1612
NOTES:
DS21921B-page 18
© 2005 Microchip Technology Inc.
MCP1612
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.
X
/XX
Device
Temperature
Range
Package
Device:
MCP1612: Synchronous Buck Regulator
MCP1612T: Synchronous Buck Regulator
(Tape and Reel)
Temperature Range:
I
Package:
MF = Dual Flat, No Lead (3x3mm Body), 8-lead
MS = Plastic MSOP, 8-lead
Examples:
a)
b)
c)
d)
MCP1612-ADJI/MS:
Industrial Temperature,
8LD MSOP package.
MCP1612T-ADJI/MS: Tape and Reel
Industrial Temperature,
8LD MSOP package.
MCP1612-ADJI/MF: Industrial Temperature,
8LD DFN package.
MCP1612T-ADJI/MF: Tape and Reel
Industrial Temperature,
8LD DFN package.
= -40°C to +85°C
© 2005 Microchip Technology Inc.
DS21921B-page 19
MCP1612
NOTES:
DS21921B-page 20
© 2005 Microchip Technology Inc.
MCP1612
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 provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED,
WRITTEN OR ORAL, STATUTORY OR OTHERWISE,
RELATED TO THE INFORMATION, INCLUDING BUT NOT
LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE,
MERCHANTABILITY OR FITNESS FOR PURPOSE.
Microchip disclaims all liability arising from this information and
its use. 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 Microchip intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, Accuron,
dsPIC, KEELOQ, microID, MPLAB, PIC, PICmicro, PICSTART,
PRO MATE, PowerSmart, rfPIC, and SmartShunt are
registered trademarks of Microchip Technology Incorporated
in the U.S.A. and other countries.
AmpLab, FilterLab, Migratable Memory, MXDEV, MXLAB,
PICMASTER, SEEVAL, SmartSensor and The Embedded
Control Solutions Company are registered trademarks of
Microchip Technology Incorporated in the U.S.A.
Analog-for-the-Digital Age, Application Maestro, dsPICDEM,
dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR,
FanSense, FlexROM, fuzzyLAB, In-Circuit Serial
Programming, ICSP, ICEPIC, Linear Active Thermistor,
MPASM, MPLIB, MPLINK, MPSIM, PICkit, PICDEM,
PICDEM.net, PICLAB, PICtail, PowerCal, PowerInfo,
PowerMate, PowerTool, rfLAB, rfPICDEM, Select Mode,
Smart Serial, SmartTel, Total Endurance and WiperLock are
trademarks of Microchip Technology Incorporated in the
U.S.A. and other countries.
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.
© 2005, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received ISO/TS-16949:2002 quality system certification for
its worldwide headquarters, design and wafer fabrication facilities in
Chandler and Tempe, Arizona and Mountain View, California in
October 2003. The Company’s quality system processes and
procedures are for its PICmicro® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
© 2005 Microchip Technology Inc.
DS21921B-page 21
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08/24/05
DS21921B-page 22
© 2005 Microchip Technology Inc.
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