THIS SPEC IS OBSOLETE
Spec No: 001-32404
Spec Title: RAPID NICD/NIMH BATTERY CHARGER AND
DC BRUSHED MOTOR CONTROLLER FOR
AUTONOMOUS APPLIANCES - AN2260
Sunset Owner: M Ganesh Raaja (GRAA
Replaced by: 001-15223
AN2260
Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for
Autonomous Appliances
e
Author: Victor Kremin
Associated Project: Yes
Associated Part Family: CY8C24xxxA
Software Version: PSoC ® Designer™ 4.2 + SP2
Related Application Notes: For a complete list of the application notes, click here.
To get the latest version of this application note, or the associated project file, please visit
http://www.cypress.com/go/AN2260.
Contents
Ob
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This application note describes an electronic controller for autonomous appliances such as screwdrivers, drills, electric
shavers, and brushing machines. The controller provides a rapid built-in NiCd/NiMH battery charge and motor powered
by batteries or an external DC supply.
Introduction
Introduction ....................................................................... 1
Device Schematic.............................................................. 2
PSoC Device Internals ...................................................... 5
Firmware ........................................................................... 6
Summary ......................................................................... 14
Related Application Notes ............................................... 14
Worldwide Sales and Design Support ............................. 16
Small autonomous electric appliances such as shavers,
screwdrivers, portable drills, and brushing and haircutting
machines are widely used. Despite the inherent
differences, all of these devices have a motor, most
typically a “classic” brushed DC motor. They also have
batteries and a built-in or external battery charger to
restore battery energy after use. Many of these devices
allow the motor to be powered directly by an external DC
supply when the battery is depleted or external power is
available.
The goal for this project is to develop a simple low-cost
design that combines a brushed DC motor controller and a
rapid NiCd/NiMH battery charger. The user interface was
kept to a minimum: there is only one push button to turn
the motor on or off and a single LED to display the battery
charge status. The controller rapidly charges batteries and
allows the motor to be powered from batteries or an
external DC supply. Controller technical specifications are
given in Table 1.
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Table 1. Controller Specifications
Item
Value
2
Capacity
0.75-2.3 A/h
Battery Charge Current:
Rapid
Trickle
1A
0.15 A
Motor Supply Voltage and Power
2.5 V, 3 W
External DC Supply Specifications
15-20 V, 0.35 A
No Use Current Consumption
40 µA
Device Schematic
so
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Battery Cells
The simplified device schematic is shown in the following figure.
Figure 1. Simplified Device Schematic
Sw3
VD1
DC supply
M1
R1
Pulsefrequency
modulator
LED
Btn1
С1
L1
Sw2
Bat
Switchmode pump
PSoC
supply
R6
R3
Signal
conditioning
ADC
MUX
R7
Vdc1
The device consists of:
Controller to implement battery charging and userinterface algorithms.
Spread spectrum pulse-frequency modulator.
Switch regulator, Sw1, L1, C1, VD1.
External DC supply inclusion-detection circuit, R1, R2.
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R5
R2
Ob
Controller
Sw1
R4
Rterm
Current sense resistor, R3.
Battery switch, Sw3.
Motor switch, M1 and Sw2, respectively.
Resistive divider, R4-R6, for motor or battery, Bat1,
voltage measurement.
Switch mode pump (SMP) to increase battery voltage
to acceptable levels for the PSoC® device.
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Analog multiplexer MUX to commutate different
analog signal sources.
Signal conditioning circuit for transforming input
signals into valuable analog-to-digital conversion
(ADC) levels.
Circuit for thermistor, Rterm, resistance measurement:
Vdc, R7.
Only one N-channel MOSFET is required, which can
be controlled directly by the device without any
translators.
The on-resistance for N-Channel transistor is less
than for P-Channel in the same price range.
The inverting converter configuration is inherently
protected from load overload due to limited energy
quantity,
which is
transferred by
inductor
charge/discharge cycles.
User interface elements: push button, Btn1, and LED.
Ob
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The external DC supply voltage can be several times
higher than nominal motor or battery voltage. This
provides two significant advantages. It reduces the
converter input current, which lowers the cost and weight
of the external DC supply. It also allows the use of thinner
connection wires and less expensive connectors. In this
mode, the step-down converter switch duty cycle is small
and the use of fixed-pulse width variable frequency control
achieves a smaller duty cycle step.
e
The step-down switch regulator can be built around
different configurations with different switch placement.
The inverting regulator configuration is used in this project
because of the following advantages:
Figure 2. Complete Device Schematic
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
The complete device schematic is shown in figure.
Because most of the analog signal processing is
implemented inside the PSoC device, only a few external
components are required. Q2A is the regulator switch.
R1R2C3 is the external power-supply detection circuit. D2
suppresses possible high voltage spikes when the switch
regulator has no load (both Q2B and Q1 are open.) Q2B is
the motor control switch. Q1 and Q3 are battery switches.
They can be single load switch (FDC6331L, FDR8521L)
from Fairchild Semiconductor.
The SMP circuit consists of D4, L2, C4, and C5 elements.
R19 completely discharges storage capacitors when the
battery is disconnected. LED D3 is directly powered by a
battery to offload the SMP when it is activated. The open
drain low output drive mode at P1[4] is used. R18 provides
logic 1 for port read-modify-write instructions when the
LED is in off state. Button SW1 uses the internal pull-up
resistor, so no external components are required. J2 is the
ISSP/debug connector.
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Figure 3. PSoC Device Internals
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
The signal conditioning circuit consists of:
PSoC Device Internals
The PSoC device’s digital and analog user module
placement is shown in Figure 3. The incremental ADC is
placed in DBB00/ASC10. The resolution is set to 11 bits
and conversion time is 4 ms. The spread-spectrum, pulsefrequency modulator (PFM) consists of a conventional
fixed-pulse width PWM source placed at DBB01. An 8-bit
PRS generator is placed at DCB02. The PWM and PRS
user modules compare outputs and are AND-ed using the
row LUT. The idea for this source was suggested in
Application Note, PWM Source - High Frequency, High
Resolution - AN2246. Figure 4 shows the PFM internal
interconnection.
PWM
Compare
PFM Output
Terminal
Count
Compare
Thermistor resistance measurements.
Level translator.
Low-pass filter (LPF) to handle the signal for the
current sense resistor.
The ADC input is multiplexed in the firmware. Depending
on the required signal source, the signal comes from
either the PGA or the LPF outputs.
This type of sense resistor signal is relatively low
(maximum 100 mV in this design). It cannot be accurately
digitized by directly using the ADC. Also, the PSoC
device’s amplifiers are not rail-to-rail on output, which
limits the usefulness of the PGA for amplification
purposes. This design uses the following technique to
remove the hardware limitations: the input signals from
port 0 analog inputs are directly passed to column analog
bus via TestMux and fed to a low-pass filter input. The
RefMux of ASC21 is set to RefLo, and RefLo level is Vss
(reference is BandGap ± BandGap). It transforms the filter
input stage in the bias-free level translator that shifts Vssrelated signals to AGND-related, which are easy to
process using the LPF as gain stage.
so
PSR
let
Clock
PGA with unity gain, which is used to buffer input
signals during the load (battery or motor) voltage.
e
Figure 4. PFM Generator Interconnection
Ob
The source forms variable number, fixed-width pulses at
the PRS repeat period, which is equal to 255 PWM output
period cycles because of the use of maximum length
polynomials. The PWM pulse duty cycle is set at 0.23. By
varying the PRS compare value in range 0…254, the duty
cycle varies from 0 to the PWM generator duty cycle, or
0.23 in this design. The pulse width duration is 1 µs, and
the minimum pulse repeat interval is 4.3 µs. Figure 5
shows the PFM output signal scope images for different
duty cycle values.
Figure 5. PFM Output Signal at Different Duty Cycles
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In this design, the filter gain is near 20.5 dB, permitting
effective utilization of the ADC dynamic range. This aspect
of switching the capacitor operation is discussed in further
detail in Application Notes, Understanding Switched
Capacitor Analog Blocks - AN2041 and Understanding
Switched Capacitor Filters - AN2168.
You may be surprised by the current sense resistor
connection: during charge or motor powering from an
external supply, the P0[6] potential is negative relative to
Vss ground. This is not a problem because the level
translator works linearly to 300 mV for negative input
signals, which is much larger than maximum current sense
resistor voltage drop (100 mV). To confirm this, Figure 6
illustrates the transfer characteristic for a bipolar input
signal (measurements were taken with a 12-bit ADC with
reduced filter gain). Note that the user can move the Vss
connection point to the left of the R11 pin, which
eliminates any negative input voltage sent to the PSoC
device pins.
Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
The slow mode main oscillator (6 MHz) in this design
reduces power consumption at runtime. The SMP trip
voltage determines the device’s supply level. It is set to
2.55 V in sleep state when the device is not used and
boosted to 4.64 V when external power is available. This
reduces switch regulator MOSFET resistive losses by
providing a higher gate voltage. The user can set another
power level (such as preset 3.25 V supply when MOSFET
with smaller threshold voltage is used).
Figure 6. Negative Voltage Measurement Transfer
Characteristic (a) and Slope Estimation (b)
2500
2000
ADC code
1500
1000
Also, the Power Setting field under Global Resources
must br set according to the selected supply voltage to
correctly load oscillator and BandGap trim values. The
CPU clock is 3 MHz, which allows the system to run from
a 2.55 V supply.
Working
area
500
0
-500
-400
-200
0
200
400
600
800
let
Control state machine
Slope starts
degrading here
2.0
Timekeeping services
Electrical values measurement routines
PFM duty cycle regulator
so
Steep slope, Counts/mV
The controller firmware consists of the following:
3.0
1.5
1.0
-400
Ob
0.5
0.0
-600
1200
Uin , mV
(a)
2.5
1000
e
Firmware
-1000
-600
-200
0
200
400
600
800
1000
1200
Uin , mV
(b)
Battery charge algorithm
Sleep and Watchdog Timer handling
Runtime debug support
The control state machine provides device operation in
different states, such as powering the motor from battery
and external supply, battery charging support, low-supply
sleep mode, and so on. Figure 7 shows the machine state
diagram. Table 2 shows information on controller states.
There are four working states (Bat Motor, Ext Motor,
Battery Charge, Sleep) and two supplemental states
(Bat Power, Ext Power).
It is useful to observe the dynamic behavior of the internal
variables (such as battery voltage and current, and state
machine state) during controller firmware debugging. The
serial transmitter, placed at DCB03, is used for this
purpose. The dedicated PC software allows users to
monitor details of the operation, which greatly simplifies
firmware debugging. The communication speed is set to
19200 bps and the transmitter is clocked by a VC2 source.
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Figure 7. State Machine Diagram
b
Bat Motor
Ext Motor
c
a
b
Ext Power
Bat Power
a
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c
b
e
d
a
Legend:
a – button is pressed;
b – external power source is connected;
c – external power source is disconnected;
d – no activity is detected for preset timeout;
e – charge has been terminated;
f – charge was not activated in this external
power cycle or battery voltage is less than
charge start voltage;
g - button pressed or battery voltage dropped
below preset threshold;
h – sleep timer interrupt was triggered;
e
a
g
f
c
Sleep
h
Bat Charge
Table 2. Controller State Descriptions
State
Description
LED Status
State Value
Bat Power
Device is battery powered
Off
0
Bat Motor
Motor is powered from battery
Off
1
Sleep
Device is in low-power sleep state
Off
8
Ext Motor
Motor is powered from external DC supply, no battery charge
Off
2
Ext Power
External DC supply is applied, motor is off
On
3
Bat Charge
Battery is charged, motor is off
Blinking
6
When the device is turned on, it enters the Bat Power
state. If the user does not press the button or if the
external power is not connected within a predefined
timeout, the Sleep state is activated. This state can be
changed if the power button is pressed or if an external
supply connection is detected. If the device is powered
from batteries and the user presses the button, the
Bat Motor state is activated and the motor is turned on.
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When the external DC supply is connected, the Ext Motor
state is activated and the motor continues to run from an
external supply, preserving battery energy and maintaining
constant voltage to the motor through the switch regulator.
When the external power supply is removed, the device
returns to Bat Motor state and the motor runs
continuously. Note that the battery voltage is controlled
when the motor is powered from battery. When the battery
voltage drops below a predefined value, the controller
turns off the motor and switches to the Bat Power state to
prevent extreme battery discharging.
Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
While the controller is in the Bat Power state and an
external supply connection is detected, it switches to
Ext Power state so it can determine if the battery is being
charged during this external supply connection cycle. If
not, it starts charging the battery by jumping to
Bat Charge state. Bat Charge state is maintained until
the battery voltage slope equals zero. Also, the controller
leaves this state when the external supply is disconnected
or if the power button is pressed, which changes the state
from Bat Power to Ext Motor.
Figure 8. Controller Operation in Different States
Start
Initialize peripherials
Service watchdog
The next charge cycle can be initiated when the power
supply is disconnected and reconnected or if the battery
voltage drops below a predefined value.
e
Send debug
information (optional)
Is state = Sleep?
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At first glance, the state machine looks too complicated
because of high branch count to implement compact code.
This can be resolved by assigning numerical values to
each state variable (by applying bit-based state
representation) and using direct bit-wise operations to
handle the most frequently used branches. Using the state
variable values from Table 2, the branches (a), (b), (c) and
(g) shown in Figure 7 are handled by several lines of ‘C’
code as follows:
Code 1. State Variables in ‘C’
if(CHECK_MAIN_SUPPLY())
{
new_state &= 0x07;
new_state |= 0x02;
}
else new_state &= ~0x06;
Measure load voltage
Sleep
Measure load current
If sleep timer IRQ
posted?
Y
N
Turn on analog part and
restore normal mode
Run state machine
The firmware switches the controller into sleep mode to
conserve current consumption when the device is not
used for 1 or 2 seconds. The device can wake up with a
1 Hz Sleep Timer interrupt or by GPIO interrupts. The
Sleep Timer interrupt is used only to clear the Watchdog
Timer; no other action is taken. The analog user modules
are turned off in such state to minimize power
consumption.
The GPIO interrupt occurs when the power button is
pressed or an external power supply is connected. This
event completely wakes up the controller by turning on the
analog user modules.
Wakeup is handled by a state machine. It jumps to a new
state depending upon the reason to wake up. After
measuring the current and voltage, the PFM duty cycle
control routines are executed in a loop. Figure 8 shows the
controller operation in sleep and non-sleep states.
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Turn off analog part and
prepare to sleep
N
Control PFM source
if (check_button_pressing())
{
new_state &= 0x03;
new_state ^= 0x01;
}
Y
As previously mentioned, the device uses dynamic power
supply management to reduce current consumption. The
power supply is set to a minimum value when in sleep
mode and increases to higher a value when in normal
mode.
The controller firmware (battery charging algorithms,
electrical values measurement routines, PFM duty cycle
regulator, etc.) includes timekeeping functions. There are
state and interval timers with 1s resolution obtained by
division VC3 interrupts at 600 Hz frequency. The precision
of these timers is determined by the accuracy of the IMOs.
The timers are primarily used by battery charging
algorithms.
Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
These timers can also be used to limit the duration of the
motor-on states (Bat Motor, Ext Motor). This prevents
overheating, as required in some applications such as
power drills. The blinking LED, debounce push button
switch, event generation, sleep periodic wakeup and
debug information transmission are implemented using a
low-accuracy Sleep Timer interrupt. The nominal interrupt
rate is 1 or 8 Hz, depending on the present state.
=
N v1 N fs
V
R5 + R6
Vl
+ N fs off 1 ;
R5 + R6 + R4 Vref
Vref
N v 2 N fs
=
V
R6
Vl
+ N fs off 1 ;
R5 + R6 + R4 Vref
Vref
∆N v = N v1 − N v 2 = N fs
R5
Vl
.
R5 + R6 + R4 Vref
Equation 1
Vl
and
Vref
are load and reference voltages
Voff 1 is ADC/PGA offset voltage
∆N v
is full-scale ADC code range
Ob
N fs
is LPF gain.
∆N c
is ADC code difference, which is proportional to
the R3 current.
Voff 2
is cumulative offset voltage, which consists of
the following components:
ADC offset - 10 mV maximum.
Vss pin supply offset, which is caused by voltage drop
on internal die resistance and is proportional to PSoC
device supply current via Vss pin. Typical values are
less than 20 mV.
LPF offset - 10 mV* GLPF , typically.
so
let
e
The controller measures battery or motor voltage,
charge/motor current and battery temperature. These
values are used during rapid battery charge and to
regulate the motor supply voltage when powered from an
external DC supply. Voltage measurement is implemented
by measuring the voltage drop on resistor R5 (see
Figure 1) using a unity-gain PGA and an ADC. The value
is measured for upper and lower R5 pins in sequence and
the difference is calculated.
GLPF
is ADC code difference, that is proportional to
Temperature measurement is implemented by measuring
the voltage drop on R7 (Figure 1) and applying, in
sequence, two different voltages to the upper R7 pin and
subtracting the results. The signal from the thermistor
comes to the ADC via the PGA with unity gain. Bias
voltages are formed using the continuous time TestMux to
apply RefHi (2.6 V) level at the first step and AGND
(1.3 V) at the next. This technique compensates for both
the ADC/PGA offset and the possible offset caused by
potential differences between the Vss internal die
connection and the lower thermistor pin. (The sources of
potential differences between the Vss internal die
connection and the lower thermistor pin are the device’s
internal die resistance, PCB voltage drop, battery pack
voltage drop upon negative lead during charge, and so
on.) Figure 9 and the following formulas illustrate how this
works.
Figure 9. The Temperature Measurement
the measured voltage without the influence of offset
voltage
Current measurement is implemented by measuring the
voltage drop at R3 (Figure 1), using the modified LPF as a
level translator and gain stage. The voltage levels for the
right and left R3 pins are measured and the difference is
calculated
to
eliminate
the
influence
of
the
LPF/ADC/supply-pin offset on measurement accuracy.
N c1 = N fs
− I ⋅ R3 ⋅ GLPF + Voff 2
Vref
N c 2 = N fs
Voff 2
Vref
∆N c = N c 2 − N c1 = N fs
Voff1
V1
V2
R7
Ideal ADC
;
+
Rterm
V0
;
I ⋅ R3 ⋅ GLPF
.
Vref
Equation 2
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
N=
t1
N fs
Rterm
V0 + Voff 1 +
(V1 − V0 ) ;
Vref
R7 + Rterm
The charge is normally terminated when the battery
voltage stops increasing; this termination criterion is
suitable for either NiCd or NiMH batteries. The integration
criterion is used for battery voltage slope analysis to get
the best noise immunity. During the first step, the
measured battery voltage is filtered using a simple IIR LPF
filter.
N fs
Rterm
V0 + Voff 1 +
(V2 − V0 ) ;
Vref
R7 + Rterm
N fs
R
∆N t = N 2 − N1 =
(V2 − V1 ) term .
Vref
R7 + Rterm
N=
t2
yj =
(1 − γ ) y j −1 + v j
Equation 4
Equation 3
are ADC codes for resistive divider
bias voltages V1 and V2 (their difference is Vbandgap or
1.3V)
∆N t is ADC code difference
y j is filter output signal j sample
v j is input voltage sample
γ, γ
< 1 is filter coefficient
This filter is characterized by the gain γ . Implementation
minimizes the influence of fixed-point rounding errors and
improves the accuracy of small voltage variation detection.
let
Voff1 and V0 are offset voltages (Voff1 is the same as in
Equation (1))
e
N t1 and N t 2
Instead of dividing/multiplying the binary shift, γ = 2
was used, where K=2. Each voltage measurement result
passes through this filter.
−K
Battery voltage slope estimation is implemented using an
integral sum calculation. This technique is used in
Application Note, A Multi-Chemistry Battery Charger AN2107 and has been adapted for this application. It
calculates the rate of increase of battery temperature.
(Please refer to AN2107 for math details.) The idea is to
calculate two integral sums from the filtered battery
voltage samples and compare them to each other. When
the new integral sum is smaller than the previous sum, the
zero/negative voltage slope is considered achieved and
rapid charge is terminated. Each integral sum consists of
the 16 samples acquired with sample intervals of 4 s.
Therefore, the battery slope is evaluated once every 64 s.
Figure 11 graphically illustrates this method. This method
provides better noise immunity because it is less
dependent on a single sample measurement result.
so
The thermistor transfer function is non-linear, but obtaining
the temperature value in linear units is not necessary for
this design because the ratio of temperature increases is
not used as rapid-charge termination criterion. Therefore,
only the temperature thresholds during the charge must be
checked. This is done by analyzing the ADC code
difference ( ∆N t ). A hysteresis is added for the bottom and
−1
upper bounds of the in/out temperature range to prevent
multiple triggers when the temperature is close to the
preset range, as shown in the following figure.
Figure 10. Temperature In-Range Checking
Ob
Icharge
Irapid
Itricle
Hysteresis
area
T1 T2
T3 T4
Tbat
The device implements the rapid charge algorithm for
NiCd/NiMH batteries. The batteries are charged by a
constant current in rapid charge mode with 1 C rate (the C
rate is the hour capacity of the battery at 600 mA) when
the battery temperature is in the allowed range. When the
battery is too hot or cold, the controller reduces the charge
current using trickle charge mode. Note that the battery
temperature is measured once per 4s using an interval
timer timeout.
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Note When the charge is finished, the controller jumps to
the Ext Power state. The regulator provides low-battery
charge current to compensate for any leakage caused by
an activated LED and the PSoC device in active state.
Sleep mode can be activated to assist.
Figure 11. Integral Slope Estimation Method
S j +1 − S j ~ a
where a − slope
The device uses the PFM duty cycle regulator to maintain
the charge current or motor voltage, depending on the
controller state (Bat Charge or Ext Motor). The regulator
is an adaptive step integrator. Figure 13 shows PFM duty
cycle regulator dataflow.
∆U 2
∆U 2
S1
S2
S3
S4
∆t
∆t
∆t
∆t
t
There is runtime debug support in the controller firmware
that can be transmitted via serial port to the PC. Runtime
debug support can monitor the state of the battery or
motor voltage, the current, the temperature, the state of
the machine and the error variable. The supplemental
Power On state with unconditional branch to Bat Power is
used to transmit the timestamp-reset command to the PC
software when the device is powered.
Ob
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Note The battery scope voltage check is locked for
five minutes after starting the rapid charge, if the battery
was not used for an extended period of time. The battery
voltage can temporarily drop after the charge starts and
can be prematurely terminated.
The regulator analyzes the difference between the preset
and the actual values (current or voltage) and tries to
minimize this difference. Also, the limiting flag is analyzed
to prevent outranging for an auxiliary parameter. For
example, the regulator allows reduced power on the motor
by limiting the windings’ current to safe values.
e
U
There are two backup termination checks. The total rapid
charge time is limited by a timer. This is to prevent
overcharging when the slope voltage check, for some
reason, does not trigger. Also, the rapid charge is instantly
terminated when battery voltage reaches the predefined
maximum value. With normal use, backup checks should
not trigger unless there is a problem with the battery. The
user can add bi-color LEDs to display this occurrence. The
charge algorithm is shown in Figure 12.
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This state is not covered in Table 2
is used only for debug purposes.
transfer of debug information by
compilation directive DEBUG to
firmware globdefs.h file.
or Figure 7 because it
You can disable the
setting a conditional
0 in the controller
The debug information is sent via serial port using the
PSoC device’s P0[11] pin. An external EIA-232 (RS-232)
level translator is required (such as MAX3221E).
Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Figure 12. Battery Charge Algorithm
Start
Initialize variables and
timers, set trickle charge
Measure battery voltage
and charge current
e
Is 4s timeout
expired?
Ob
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let
Reinitialize 4s timer,
measure battery
temperature
N
Is temperature
OK?
Set trickle charge, reset
charge termination check,
suspend total charge timer
Y
Set rapid charge,
resume total charge timer
Regulate charge current
Is Vbat > Vbat_max
Y
Stop,
overvoltage error
Y
Stop,
timeout error
Y
Stop, charge
completed well
N
Is tcharge > ttotal
N
N
Is zero voltage
slope detected?
Y
N
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Is charge longer
than 300s?
Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Figure 13. Duty Cycle Regulator
Actual
−
Limiting
Step
estimator
(lookup)
Limiting
control
Range
checking
Duty
cycle
State and error conditions can also be viewed. The
software allows users to store and compare collected data
for further analysis. Figure 14 shows examples of the
graphs. The software was written using Borland®
Delphi™7.
Ob
so
let
The PC software that monitors the system is a multithread
Windows application. It is simplified in AN2107 A
Multi-Chemistry Battery Charger and allows users to view
graphs displaying battery or motor supply voltage,
charge/motor current, and temperature.
+
e
Preset
Figure 14. Example of Software Interface
Note Battery was slightly discharged before charging began.
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Document No. 001-32404 Rev. *C
13
Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Figure 15. Device Photograph
Summary
Charge algorithm can be adapted to support LiIon
batteries.
Current sense resistor can be eliminated. Battery
charge current can be found mathematically by
measuring the switch regulator input, the output
voltages and using the switch regulator look-up table.
NiCd/NiMH batteries are not very sensitive to the
absolute value of the charge current, and 10-15
percent can be tolerated without problems.
e
This application note describes a simple, low-cost battery
charger with a DC motor controller. The hardware and
firmware can be easily adapted to meet end application
demands. The following modifications can be
implemented:
Ob
so
let
Related Application Notes
AN2041 - Understanding
Capacitor Analog Blocks
AN2168 - PSoC®
Capacitor Filters
1
PSoC®
1
Switched
Understanding
Switched
AN2246 - PSoC® 1 – PWM Source – High Frequency,
High Resolution
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
Document History
Document Title: Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances - AN2260
Document Number: 001-32404
Revision
**
ECN
3023712
Orig. of
Change
YARD_UKR
Submission
Date
10/08/2007
Description of Change
OLD APP. NOTE: Obtain spec. # for note to be added to spec. system.
Updated copyright.
Added source disclaimer, revision disclaimer.
*A
3203476
BIOL_UKR
03/23/2011
Updated the BOOT.TPL file and UM versions.
*B
4333178
GRAA
04/04/2014
Updated in new template.
Completing Sunset Review.
4737703
GRAA
04/23/2015
Obsolete document.
e
*C
Ob
so
let
Completing Sunset Review.
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Document No. 001-32404 Rev. *C
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Rapid NiCd/NiMH Battery Charger and DC Brushed Motor Controller for Autonomous Appliances
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Document No. 001-32404 Rev. *C
16