MCP2021A/2A
LIN Transceiver with Voltage Regulator
Features:
Description:
• The MCP2021A/2A are compliant with LIN Bus
Specifications Version 1.3, 2.1 and with SAE
J2602-2
• Support Baud Rates up to 20 kBaud
• 43V Load Dump Protected
• Maximum Continuous Input Voltage: 30V
• Wide LIN-Compliant Supply Voltage: 6.0 – 18.0V
• Extended Temperature Range: -40 to +125°C
• Interface to PIC® MCU EUSART and Standard
USARTs
• Wake-Up on LIN Bus Activity or Local Wake Input
• Local Interconnect Network (LIN) Bus Pin:
- Internal Pull-Up Termination Resistor and
Diode for Slave Node
- Protected Against VBAT Shorts
- Protected Against Loss of Ground
- High-Current Drive
• TXD and LIN Bus Dominant Time-Out Function
• Two Low-Power Modes:
- Transmitter Off: 90 µA (typical)
- Power Down: 4.5 µA (typical)
• Output Indicating Internal Reset State (POR or
Sleep Wake)
• MCP2021A/2A On-Chip Voltage Regulator:
- Output Voltage of 5.0V or 3.3V
at 70 mA Capability with Tolerances of ±3%
Over the Temperature Range
- Internal Short Circuit Current Limit
- External Components Limited to Filter
Capacitor and Load Capacitor
• Automatic Thermal Shutdown
• High Electromagnetic Immunity (EMI), Low
Electromagnetic Emission (EME)
• Robust ESD Performance: ±15 kV for LBUS and
VBB pin (IEC61000-4-2)
• Transient Protection for LBUS and VBB Pins in
Automotive Environment (ISO7637)
• Meets Stringent Automotive Design
Requirements, including “OEM Hardware
Requirements for LIN, CAN and FlexRay
Interfaces in Automotive Applications”, Version
1.2, March 2011
• Multiple Package Options, including Small
4x4 mm DFN Package
The MCP2021A/2A provide a bidirectional, half-duplex
communication physical interface to meet the LIN bus
specification Revision 2.1 and SAE J2602-2. The
devices incorporate a voltage regulator with 5V or 3.3V
at 70 mA regulated power supply output. The devices
have been designed to meet the stringent quiescent
current requirements of the automotive industry and
will survive +43V load dump transients and double
battery jumps.
2012-2014 Microchip Technology Inc.
Package Types
MCP2021A
PDIP, SOIC
RXD
CS/LWAKE
VREG
TXD
1
2
3
4
FAULT/TXE
VBB
LBUS
VSS
8
7
6
5
MCP2021A
4x4 DFN
RXD 1
CS/LWAKE 2
VREG 3
TXD 4
EP
9
8 FAULT/TXE
7 VBB
6 LBUS
5 VSS
MCP2022A
PDIP, SOIC, TSSOP
RXD
CS/LWAKE
VREG
TXD
RESET
NC
NC
1
2
3
4
5
6
7
14
13
12
11
10
9
8
FAULT/TXE
VBB
LBUS
VSS
NC
NC
NC
* Includes Exposed Thermal Pad (EP), see Table 1-2.
DS20002298C-page 1
MCP2021A/2A
MCP2021A/2A Block Diagram
VREG
RESET
(MCP2022A only)
Thermal
Protection
Short Circuit
Protection
Voltage
Regulator
VBB
Ratiometric
Reference
VREG
Internal Circuits
VREG
4.2V
Wake-Up Logic
and
Power Control
Bus Wake-Up
RXD
~ 30 k
Slope Control
CS/LWAKE
LBUS
TXD
Bus
Dominant
Timer
FAULT/TXE
VSS
Thermal and
Short Circuit
Protection
DS20002298C-page 2
2012-2014 Microchip Technology Inc.
MCP2021A/2A
1.0
DEVICE OVERVIEW
1.1
The MCP2021A/2A devices provide a physical
interface between a microcontroller and a LIN
half-duplex bus. They are intended for automotive and
industrial applications with serial bus baud rates up to
20 kBaud. These devices will translate the CMOS/TTL
logic levels to LIN logic levels and vice versa.
Modes of Operation
The MCP2021A/2A work in five modes: Power-On
Reset, Power-Down, Ready, Operation and
Transmitter Off. For an overview of all operational
modes, please refer to Table 1-1. For the operational
mode transition, please refer to Figure 1-1.
The MCP2021A/2A offer optimum EMI and ESD
performance and can withstand high voltage on the LIN
bus. The devices support two low-power modes to
meet automotive industry power consumption
requirements. The MCP2021A/2A also provide a +5V
or 3.3V regulated power output at 70 mA.
FIGURE 1-1:
STATE DIAGRAM
CS/LWAKE = 0
POR(2)
VREG OFF
RX OFF
TX OFF
VBB > VON
READY
VREG ON
RX ON
TX OFF
CS/LWAKE = 1 &
FAULT/TXE = 1 (3) &
TXD = 1&
VREG_OK = 1 (1)
CS/LWAKE = 1&
FAULT/TXE = 0&
CS/LWAKE = 1 OR
Voltage Rising Edge on LBUS
TX OFF
VREG ON
RX ON
TX OFF
CS/LWAKE = 1&
FAULT/TXE = 1 (3)&
TXD = 1
CS/LWAKE = 0
POWER-DOWN
VREG OFF
RX OFF
TX OFF
CS/LWAKE = 1&
FAULT/TXE = 0
OPERATION
VREG ON
RX ON
TX ON
CS/LWAKE = 0
Note 1: VREG_OK: Regulator Output Voltage > 0.8VREG_NOM.
2: If the voltage on pin VBB falls below VOFF, the device will enter Power-On Reset mode from all other
modes, which is not shown in the figure.
3: FAULT/TXE = 1 represents input high and no fault conditions. FAULT/TXE = 0 represents input low or a
fault condition. Refer to Table 1-5.
2012-2014 Microchip Technology Inc.
DS20002298C-page 3
MCP2021A/2A
1.1.1
POWER-ON RESET MODE
Upon application of VBB or whenever the voltage on
VBB is below the threshold of regulator turn-off voltage
VOFF (typically 4.50V), the device enters Power-On
Reset (POR) mode. During this mode, the device
maintains the digital section in a Reset mode and waits
until the voltage on the VBB pin rises above the
threshold of regulator turn-on voltage VON (typically
5.75V) to enter Ready mode. In Power-On Reset
mode, the LIN physical layer and voltage regulator are
disabled and the RESET output (MCP2022A only) is
forced to low.
1.1.2
READY MODE
The device enters Ready mode from POR mode after
the voltage on VBB rises above the threshold of
regulator turn-on voltage VON or from Power-Down
mode when a remote or local wake-up event happens.
Upon entering Ready mode, the voltage regulator and
the receiver section of the transceiver are powered up.
The transmitter remains in an off state. The device is
ready to receive data but not to transmit. In order to
minimize the power consumption, the regulator
operates in a reduced-power mode. It has a lower
GBW product and it is thus slower. However, the 70 mA
drive capability is unchanged.
The device stays in Ready mode until the output of the
voltage regulator has stabilized and the CS/LWAKE pin
is high (‘1’).
1.1.3
OPERATION MODE
If VREG is OK (VREG > 0.8 VREG_NORM) and the
CS/LWAKE, FAULT/TXE and TXD pins are high, the
part enters Operation mode from either Ready or
Transmitter Off mode.
In this mode, all internal modules are operational. The
internal pull-up resistor between LBUS and VBB is
connected only in this mode.
The device goes into Power-Down mode at the falling
edge on CS/LWAKE or into Transmitter Off mode at the
falling edge on FAULT/TXE while CS/LWAKE stays
high.
DS20002298C-page 4
1.1.4
TRANSMITTER OFF MODE
In Transmitter Off mode, the receiver is enabled but the
LBUS transmitter is off. It is a lower power mode.
In order to minimize power consumption, the regulator
operates in a reduced-power mode. It has a lower
GBW product and it is thus slower. However, the 70 mA
drive capability is unchanged.
The transmitter may be re-enabled whenever the
FAULT/TXE signal returns high, by removing the
internal fault condition and by driving FAULT/TXE high.
The transmitter will not be enabled even if the
FAULT/TXE pin is brought high externally, when the
internal fault is still present. However, externally forcing
the FAULT/TXE high while the internal fault is still
present should be avoided, since this will induce high
current and power dissipation in the FAULT/TXE pin.
The transmitter is also turned off whenever the voltage
regulator is unstable or recovering from a fault. This
prevents unwanted disruption of the bus during times of
uncertain operation.
1.1.5
POWER-DOWN MODE
In Power-Down mode, the transceiver and the voltage
regulator are both off. Only the bus wake-up section
and the CS/LWAKE pin wake-up circuits are in
operation. This is the lowest power mode.
If any bus activity (e.g., a Break character) occurs
during Power-Down mode, the device will immediately
enter Ready mode and enable the voltage regulator.
Then, once the regulator output has stabilized
(approximately 0.3 ms to 1.2 ms), it goes into
Operation mode. Refer to Section 1.1.6 “Remote
Wake-Up”.
The part will also enter Ready mode from Power-Down
mode, followed by the Operation mode, if the
CS/LWAKE pin becomes active high (‘1’).
1.1.6
REMOTE WAKE-UP
The Remote Wake-Up sub-module observes the LBUS
in order to detect bus activity. In Power-Down mode,
normal LIN recessive/dominant threshold is disabled
and the LIN bus wake-up voltage threshold VWK(LBUS)
is used to detect bus activities. Bus activity is detected
when the voltage on the LBUS falls below the LIN bus
wake-up voltage threshold VWK(LBUS) (approximately
3.5V) for at least tBDB (a typical duration of 80 µs)
followed by a rising edge. Such a condition causes the
device to leave Power-Down mode.
2012-2014 Microchip Technology Inc.
MCP2021A/2A
TABLE 1-1:
State
OVERVIEW OF OPERATIONAL MODES
Transmitter Receiver
Internal
Voltage
Wake
Regulator
Module
Operation
Comments
POR
OFF
OFF
OFF
OFF
Proceed to Ready mode after
VBB > VON
Ready
OFF
ON
OFF
ON
If CS/LWAKE is high, then proceed to Bus Off
Operation or Transmitter Off mode.
state
Operation
ON
ON
OFF
ON
If CS/LWAKE is low, then proceed to
Power-Down mode.
If FAULT/TXE is low, then proceed to
Transmitter Off mode.
Power-Down
OFF
OFF
ON
Activity
Detect
OFF
On LIN bus rising edge or CS/LWAKE Lowest
high level, go to Ready mode.
power mode
Transmitter Off
OFF
ON
OFF
ON
If CS/LWAKE is low, then proceed to
Power-Down mode.
If FAULT/TXE is high, then proceed to
Operation mode.
2012-2014 Microchip Technology Inc.
Normal
Operation
mode
Bus Off
state,
lower power
mode
DS20002298C-page 5
MCP2021A/2A
1.2
Pin Descriptions
The descriptions of the pins are listed in Table 1-2.
TABLE 1-2:
PIN FUNCTION TABLE
Pin Number
Pin Name
8-lead
PDIP, SOIC
14-lead
PDIP, SOIC, TSSOP
Pin Type
4x4 DFN
RXD
1
1
1
Output
CS/LWAKE
2
2
2
TTL Input,
HV-tolerant
VREG
3
3
3
TXD
4
4
4
Description
Receive Data Output
Output
Chip Select and Local Wake-up
Input
Voltage Regulator Output
Input, HV-tolerant Transmit Data Input
RESET
—
—
5
Output
NC
—
—
6–10
—
Reset Output
No Connection
VSS
5
5
11
Power
Ground
LBUS
6
6
12
I/O, HV
LIN Bus
Battery
VBB
7
7
13
Power
FAULT/TXE
8
8
14
I/O, HV-tolerant
EP
—
9
—
—
1.2.1
RECEIVE DATA OUTPUT (RXD)
1.2.3
Fault Detect Output/Transmitter
Enable Input
Exposed Thermal Pad
POWER OUTPUT (VREG)
Receive Data Output pin. The RXD pin is a standard
CMOS output pin and it follows the state of the LBUS
pin.
Positive Supply Voltage Regulator Output pin. An
on-chip LDO gives +5.0 or +3.3V at 70 mA regulated
voltage on this pin.
1.2.2
1.2.4
CHIP SELECT AND LOCAL
WAKE-UP INPUT (CS/LWAKE)
Chip Select and Local Wake-up Input pin (TTL level,
high-voltage tolerant). This pin controls the device state
transition. Refer to Figure 1-1.
If CS/LWAKE = 1, the device can work in Operation
mode (FAULT/TXE = 1) or in Transmitter Off mode
(FAULT/TXE = 0). If CS/LWAKE = 0, the device can
work in Power-Down mode or in Ready mode.
An internal pull-down resistor will keep the CS/LWAKE
pin low to ensure that no disruptive data will be present
on the bus while the microcontroller is executing a
Power-On Reset and I/O initialization sequence. When
CS/LWAKE is ‘1’, a weak pull-down (~600 kΩ) is used
to reduce current. When CS/LWAKE is ‘0’, a stronger
pull-down (~300 kΩ) is used to maintain the logic level.
This pin may also be used as a local wake-up input
(see Figure 1-1). The microcontroller will set the I/O pin
to control the CS/LWAKE. An external switch or
another source can then wake up both the transceiver
and the microcontroller.
Note:
CS/LWAKE should NOT be tied directly to
the VREG pin as this could force the
MCP2021A/2A into Operation mode
before the microcontroller is initialized.
DS20002298C-page 6
TRANSMIT DATA INPUT (TXD)
Transmit Data Input pin (TTL level, HV-compliant,
adaptive pull-up). The transmitter reads the data
stream on the TXD pin and sends it to the LIN bus. The
LBUS pin is low (dominant) when TXD is low and high
(recessive) when TXD is high.
TXD is internally pulled up to approximately 4.2V. When
TXD is ‘0’, a weak pull-up (~900 kΩ) is used to reduce
current. When TXD is ‘1’, a stronger pull-up (~300 kΩ)
is used to maintain the logic level. A series
reverse-blocking diode allows applying TXD input
voltages greater than the internally generated 4.2V and
renders the TXD pin HV-compliant up to 30V (see
MCP2021A/2A Block Diagram).
1.2.5
RESET (MCP2022A ONLY)
RESET output pin. This pin is open-drain with ~90 kΩ
pull-up to VREG. It indicates the internal voltage has
reached a valid, stable level. As long as the internal
voltage is valid (above 0.8 VREG), this pin will remain
high (‘1’); otherwise, the RESET pin switches to low
(‘0’).
1.2.6
NO CONNECTION (NC)
No internal connection.
2012-2014 Microchip Technology Inc.
MCP2021A/2A
1.2.7
GROUND (VSS)
1.2.10
Ground pin.
1.2.8
LIN BUS (LBUS)
Fault Detect Output/Transmitter Enable Input pin. The
output section is HV-tolerant open-drain (up to 30V).
The input section is identical to the TXD section (TTL
level, HV-compliant, adaptive pull-up). The internal
pull-up resistor may be too weak for some applications.
We recommend adding a 10 k external pull-up
resistor to ensure a logic high level. Its state is defined
as shown in Table 1-5. The device is placed in
Transmitter Off mode whenever this pin is low (‘0’),
either from an internal fault condition or by external
drive.
LIN Bus pin. LBUS is a bidirectional LIN bus interface
pin and is controlled by the signal TXD. It has an open
collector output with a current limitation. To reduce
electromagnetic emission, the slopes during signal
changes are controlled and the LBUS pin has
corner-rounding control for both falling and rising
edges.
The internal LIN receiver observes the activities on the
LIN bus and generates the output signal RXD that
follows the state of the LBUS. A 1st degree 160 kHz
low-pass input filter optimizes electromagnetic
immunity.
1.2.9
FAULT DETECT
OUTPUT/TRANSMITTER ENABLE
INPUT (FAULT/TXE)
If CS/LWAKE is high (‘1’), the FAULT/TXE signals a
mismatch between the TXD input and the LBUS level.
This can be used to detect a bus contention. Since the
bus exhibits a propagation delay, the sampling of the
internal compare is debounced to eliminate false faults.
BATTERY POSITIVE SUPPLY
VOLTAGE (VBB)
After the device wakes up, the FAULT/TXE indicates
what wakes the device if CS/LWAKE remains low (‘0’)
(refer to Table 1-5).
Battery Positive Supply Voltage pin. An external diode
is connected in series to prevent the device from being
reversely powered (refer to Figure 1-7).
The FAULT/TXE pin sampled at a rate faster than every
10 µs.
TABLE 1-3:
FAULT/TXE TRUTH TABLE
FAULT/TXE
TXD
In
RXD
Out
LINBUS
I/O
Thermal
Override
External
Input
Definition
Driven
Output
CS = 1
VBB
OFF
H
L
FAULT, TXD driven low, LBUS shorted to VBB (Note 1)
or LBUS/TXD permanent dominant detected and Transmit time-out shutdown.
H
H
OK
H
H
OK
L
H
H
H
VBB
OFF
L
L
GND
OFF
H
L
GND
OFF
H
H
OK, data is being received from LBUS
x
x
VBB
ON
H
L
FAULT, Transceiver in thermal shutdown
x
x
VBB
x
L
x
NO FAULT, the CPU is commanding the transceiver
to turn off the transmitter driver
CS = 0
x
x
x
x
x
L
Wake-up from LIN bus activity
x
x
x
x
x
H
Wake-up from POR
Legend: x = Don’t care
Note 1: The FAULT/TXE is valid after approximately 25 µs after the TXD falling edge. This is to eliminate false fault
reporting during bus propagation delays.
2012-2014 Microchip Technology Inc.
DS20002298C-page 7
MCP2021A/2A
1.3
1.3.3
Fail-Safe Features
1.3.1
GENERAL FAIL-SAFE FEATURES
• An internal pull-down resistor on CS/LWAKE pin
disables the transmitter if the pin is floating.
• An internal pull-up resistor on the TXD pin places
TXD in high and the LBUS in recessive if the TXD
pin is floating.
• High-impedance and low-leakage current on LBUS
during loss of power or ground.
• The current limit on LBUS protects the transceiver
from being damaged if the pin is shorted to VBB.
1.3.2
THERMAL PROTECTION
The thermal protection circuit monitors the die
temperature and is able to shut down the LIN
transmitter and voltage regulator.
There are three causes for a thermal overload. A
thermal shutdown can be triggered by any one, or a
combination of, the following thermal overload
conditions:
• Voltage regulator overload
• LIN bus output overload
• Increase in die temperature due to increase in
environment temperature
The recovery time from the thermal shutdown is equal
to adequate cooling time.
Driving the TXD and checking the RXD pin make it
possible to determine whether there is a bus contention
(TXD = high, RXD = low) or a thermal overload
condition (TXD = low, RXD = high).
FIGURE 1-2:
THERMAL SHUTDOWN
STATE DIAGRAMS
Output
Overload
Voltage
Regulator
Shutdown
LIN Bus
Shorted to
VBB
Operation
Mode
Transmitter
Shutdown
Temp < SHUTDOWNTEMP Temp < SHUTDOWNTEMP
The LIN bus can be driven to a dominant level either
from the TXD pin or externally. An internal timer
deactivates the LBUS transmitter if a dominant status
(low) on the LIN bus lasts longer than Bus Dominant
Time-out
Time,
tTO(LIN)
(approximately
20 milliseconds). At the same time, the RXD output is
put in recessive (high), FAULT/TXE is also driven to low
and the internal LIN pull-up resistor is disconnected.
The timer is reset on any recessive LBUS status or POR
mode. The recessive status on LBUS can be caused
either by the bus being externally pulled up or by the
TXD pin being returned high.
1.4
Internal Voltage Regulator
The MCP2021A/2A have a positive regulator capable
of supplying +5.00 or +3.30 VDC ±3% at up to 70 mA of
load current over the entire operating temperature
range of -40°C to +125°C. The regulator uses a LDO
design, is short-circuit-protected and will turn the
regulator output off if its output falls below the shutdown
voltage threshold, VSD.
With a load current of 70 mA, the minimum input to
output voltage differential required for the output to
remain in regulation is typically +0.5V (+1V maximum
over the full operating temperature range). Quiescent
current is less than 100 µA with a full 70 mA load
current when the input to output voltage differential is
greater than +3.00V.
Regarding the correlation between VBB, VREG and IDD,
please refer to Figures 1-4 and 1-5. When the input
voltage (VBB) drops below the differential needed to
provide stable regulation, the voltage regulator output,
VREG, will track the input down to approximately VOFF,
at which point the regulator will turn off the output. This
will allow PIC® microcontrollers with internal POR
circuits to generate a clean arming of the POR trip
point. The MCP2021A/2A will then monitor VBB and
turn on the regulator when VBB is above the threshold
of regulator turn-on voltage, VON.
In Power-Down mode, the VBB monitor is turned off.
Under specific ambient temperature and battery
voltage range, the voltage regulator can output as high
as 150 mA current. For current load capability of the
voltage regulator, refer to Figures 2-8 and 2-9.
Note:
DS20002298C-page 8
TXD/LBUS TIME-OUT TIMER
The regulator has an overload current limit
of approximately 250 mA. The regulator
output voltage, VREG, is monitored. If
output voltage VREG is lower than VSD, the
voltage regulator will turn off. After a
recovery time of about 3 ms, the VREG will
be checked again. If there is no short
circuit (VREG > VSD), then the voltage
regulator remains on.
2012-2014 Microchip Technology Inc.
MCP2021A/2A
The regulator requires an external output bypass
capacitor for stability. See Figure 2-1 for correct
capacity and ESR for stable operation.
Note:
TABLE 1-4:
A ceramic capacitor of at least 10 µF or a
tantalum capacitor of at least 2.2 µF is
recommended for stability.
In worst-case scenarios, the ceramic capacitor may
derate by 50%, based on tolerance, voltage and
temperature. Therefore, in order to ensure stability,
ceramic capacitors smaller than 10 µF may require a
small series resistance to meet the ESR requirements,
as shown in Table 1-4.
FIGURE 1-3:
RECOMMENDED SERIES
RESISTANCE FOR CERAMIC
CAPACITORS
Resistance
Capacitor
1
1 µF
0.47
2.2 µF
0.22
4.7 µF
0.1
6.8 µF
VOLTAGE REGULATOR BLOCK DIAGRAM
Pass
Element
VREG
VBB
Sampling
Network
Fast
Transient
Loop
Buffer
VSS
VREF
2012-2014 Microchip Technology Inc.
DS20002298C-page 9
MCP2021A/2A
FIGURE 1-4:
VOLTAGE REGULATOR OUTPUT ON POWER-ON RESET
VBB
V
8
Minimum VBB to maintain regulation
VON
6
VOFF
4
2
0
t
VREG
V
5
VREG-NOM
4
3
2
1
0
t
Note 1:
2:
3:
4:
FIGURE 1-5:
(4)
(1)
(2)
(3)
Start-up, VBB < VON, regulator off.
VBB > VON, regulator on.
VBB Minimum VBB to maintain regulation.
VBB < VOFF, regulator will turn off.
VOLTAGE REGULATOR OUTPUT ON OVERCURRENT PROTECTION
IREG
mA
lLIM
0
t
VREG
6
5
V
VREG-NOM
4
VSD
3
2
1
0
Note 1:
2:
t
(1)
(2)
IREG less than lLIM, regulator on.
After IREG exceeds lLIM, the voltage regulator output will be reduced until VSD is reached.
DS20002298C-page 10
2012-2014 Microchip Technology Inc.
MCP2021A/2A
1.5
1.5.1
Optional External Protection
V RECESSIVE
R TP ---------------------------------I REGMAX
REVERSE BATTERY PROTECTION
An external reverse-battery-blocking diode should be
used to provide polarity protection (see Figure 1-7).
1.5.2
EQUATION 1-2:
TRANSIENT VOLTAGE
PROTECTION (LOAD DUMP)
An external 43V transient suppressor (TVS) diode,
between VBB and ground, with a transient protection
resistor (RTP) in series with the battery supply and the
VBB pin, protects the device from power transients and
ESD events greater than 43V (see Figure 1-7). The
maximum value for the RTP protection resistor depends
upon two parameters: the minimum voltage the part will
start at and the impacts of this RTP resistor on the VBB
value, thus on the bus recessive level and slopes.
This leads to a set of three equations to fulfill.
Equation 1-1 provides a maximum RTP value
according to the minimum battery voltage the user
wants.
Equation 1-2 provides a maximum RTP value
according to the maximum error on the recessive level,
thus VBB, since the part uses VBB as the reference
value for the recessive level.
Equation 1-3 provides a maximum RTP value
according to the maximum relative variation the user
can accept on the slope when IREG varies.
Since both Equations 1-1 and 1-2 must be fulfilled, the
maximum allowed value for RTP is thus the smaller of
the two values found when solving Equations 1-1
and 1-2.
Usually Equation 1-1 gives the higher constraint
(smaller value) for RTP, as shown in the following
example where VBATmin is 8V.
However, the user needs to check that the value found
with Equation 1-1 fulfills Equations 1-2 and 1-3.
While this protection is optional, it should be
considered as good engineering practice.
EQUATION 1-1:
Where:
VRECESSIVE = Maximum variation tolerated on
the recessive level
Assume VRECESSIVE = 1V and IREGMAX = 50 mA.
Equation 1-2 shows 20.
EQUATION 1-3:
Slope VBATmin – 1V
RTP --------------------------------------------------------------I REGMAX
Where:
Slope = Maximum variation tolerated on the
slope level
IREGMAX = Maximum current the current will
provide to the load
VBATmin > VOFF + 1.0V
Assume
Slope = 15%,
VBATMIN = 8V
IREGMAX = 50 mA. Equation 1-2 shows 20.
1.5.3
and
CBAT CAPACITOR
Selecting CBAT = 10 x CREG is recommended.
However, this leads to a high value capacitor. Lower
values for CBAT capacitor can be used with respect to
some rules. In any case, the voltage at the VBB pin
should remain above VOFF when the device is turned
on.
The current peak at start-up (due to the fast charge of
the CREG and CBAT capacitors) may induce a
significant drop on the VBB pin. This drop is
proportional to the impedance of the VBAT connection
(see Figure 1-7).
The VBAT connection is mainly inductive and resistive.
Therefore, it can be modeled as a resistor (RTOT) in
series with an inductor (L). RTOT and L can be
measured.
V BATmin – 5.5V
R TP -------------------------------------250 mA
The following formula gives an indication of the
minimum value of CBAT using RTOT and L:
5.5V = V OFF + 1.0V
EQUATION 1-4:
Where:
CBAT
-------------- =
C REG
250 mA = Peak current at power-on when
VBB = 5.5V
2
2
100L + R TOT
-----------------------------------2
R TOT
2
1 + L + ------------100
Where:
Assume VBATmin = 8V. Equation 1-1 shows 10
L = Inductor (measured in mH)
RTOT = RLINE + RTP (measured in )
2012-2014 Microchip Technology Inc.
DS20002298C-page 11
MCP2021A/2A
Equation 1-4 allows lower CBAT/CREG values than the
10x ratio we recommend.
Assume that we have a good quality VBAT connection
with RTOT = 0.1 and L = 0.1 mH.
Solving the equation gives CBAT/CREG = 1.
If we increase RTOT up to 1 the result becomes
CBAT/CREG = 1.4. However, if the connection is highly
resistive or highly inductive (poor connection), the
CBAT/CREG ratio greatly increases.
TABLE 1-5:
CBAT/CREG RATIO BY VBAT
CONNECTION TYPE
Connection
Type
RTOT
L
CBAT/CREG
Ratio
Good
0.1
0.1 mH
1
Typical
1
0.1 mH
1.4
Highly inductive
0.1
1 mH
7
Highly resistive
10
0.1 mH
7
Figure 1-6 shows the minimum recommended
CBAT/CREG ratio as a function of the impedance of the
VBAT connection.
FIGURE 1-6:
MINIMUM
RECOMMENDED
CBAT/CREG RATIO
CBAT/CREG
10
RBAT
BAT=10
=0.1
R
RBAT
BAT=4
=0.3
R
BAT=2
RBAT
=1
R
RBAT=1
RBAT=0.3
RBAT=0.1
1
0.1
VBAT Line Inductance [mH]
DS20002298C-page 12
1
2012-2014 Microchip Technology Inc.
MCP2021A/2A
1.6
Typical Applications
FIGURE 1-7:
TYPICAL APPLICATION CIRCUIT
VBAT
VBAT
RTP
220 k
43V (5)
CBAT
VBB
CREG
Wake-Up
VDD
VBB
VREG
TXD
TXD
1 k
(6)
RXD
RXD
I/O
Microcontroller
I/O
Master Node Only
LIN Bus
LBUS
CS/LWAKE
(3)
MMBZ27V (4)
FAULT/TXE
220 pF
I/O
RESET
RESET
VSS
VSS
100 nF
Note 1: CREG, the load capacitor, should be ceramic or tantalum rated for extended temperatures, 1.0 – 22 µF.
See Figure 2-1 to select the correct ESR.
2: CBAT is the filter capacitor for the external voltage supply. Typically 10 x CREG, with no ESR restriction.
See Figure 1-6 to select the minimum recommended value for CBAT. The RTP value is added to the line
resistance.
3: This diode is only needed if CS/LWAKE is connected to the VBAT supply.
4: ESD protection diode.
5: This component is for additional load dump protection.
6: An external 10 kΩ resistor is recommended for some applications.
FIGURE 1-8:
TYPICAL LIN NETWORK CONFIGURATION
40m
+ Return
LIN bus
1 k
VBB
LIN bus
MCP202XA
LIN bus
MCP205X
Slave 1
(MCU)
LIN bus
MCP202XA
Slave 2
(MCU)
LIN bus
MCP2003
Slave n