DALLAS DS1227S

DS1227
DS1227
KickStarter Chip
FEATURES
• Provides
PIN ASSIGNMENT
step-up regulation and microenergy
management for battery-operated systems
VCCO2
• Converts +3V to +6V DC input power source to +5V
1
20
VCCO4
VCCO3
2
19
MODE4
VCCO1
3
18
SENSE
PWRON
4
17
INT/ACK
VDCO
5
16
OSCEXT
VDCI
6
15
BOOST
7
14
ON1
8
13
ON4
9
12
RXIN
10
11
RXOUT
DC out for system power
• “Kickstarts” system power upon detection of external
stimuli:
-
Clock/calendar alarm
Sensor trip; such as from a photo diode
Incoming activity to a serial port
Any low-level signal transition
GND
• Shuts
ON/OFF3
down microcontroller power under software
control when operation complete
OFF1
• Provides 3 auxiliary power outputs for independent
ON2/OFF2
powering of system functions
20-Pin DIP (300 Mil)
See Mech. Drawing - Sect. 16, Pg. 1
• Allows design of “power on demand” systems
• Insures maximum life of main power source
• Ideally suited for DS5000-based systems
• Available in 20-pin DIP or SOIC packages
• Operating temperature range of –40°C to +85°C
VCCO2
1
20
VCCO4
VCCO3
2
19
MODE4
VCCO1
3
18
SENSE
PWRON
4
5
17
16
6
15
7
14
13
ON1
12
RXIN
11
RXOUT
VDCO
VDCI
GND
ON/OFF3
OFF1
ON2/OFF2
8
9
10
INT/ACK
OSCEXT
BOOST
ON4
20-Pin SOIC (300 Mil)
See Mech. Drawing - Sect. 16, Pg. 6
ORDERING INFORMATION
DS1227:
DS1227S:
20-Pin DIP
20-Pin SOIC
DESCRIPTION
The DS1227 Kickstarter is a unique CMOS circuit which
combines power conversion and microenergy management functions for battery operated systems. Using its
integral DC-DC converter, the DS1227 supplies +5V on
demand from either a 3– or 6–volt battery input. The primary +5V output, typically tied to the microcontroller’s
VCC pin, is “kickstarted” on in response to any one of
several possible momentary, external signal transitions.
Two auxiliary +5V power supply outputs can then be independently enabled or disabled under software control. When the primary power supply output is disabled,
also under software control, the auxiliary power supply
outputs remain in the state selected. In this manner, individual portions of the system can be powered only
022698 1/20
DS1227
when they are required, minimizing the energy consumption of the system.
The Kickstarter activates or kickstarts the primary VCC
output in response to external momentary low-going
signals. Examples of such signals include a clock/calendar alarm from a DS1283 Watchdog Timekeeper, or
an incoming asynchronous serial data word from a host
PC via the DS1275 Line Powered Transceiver, or a simple pushbutton switch.
circuit. In this case, the Kickstarter can be signalled at
regular intervals, typically from a DS1283 Watchdog
Timekeeper, to momentarily apply power to the sensor
and monitor an input for an active response.
An application using the Kickstarter has the capability to
wake-up from a ultra-low power state, perform a task using minimum energy, and then go back to sleep until the
DS1227 is signalled to kickstart system operation once
again.
In addition, the DS1227 kickstarts primary system power in response to activity detected by an external sensor
PIN DESCRIPTION
PIN
I/O
DESCRIPTION
BOOST
Input
VDCO
Output
Regulation mode control.
VDCI
Input
GND
-
VCCO1
Output
ON1
Input
INT/ACK
Input/Output
OFF1
Input
PWRON1
Output
VCCO1 Power On signal output; Indicates when VCCO1 is powered on; Sometimes required for controlling external tri-state buffers in systems where microenergy management techniques are employed.
Auxiliary switched supply voltage outputs.
Main DC supply voltage output.
Main DC supply voltage input.
System ground.
Primary switched supply voltage output.
On control for VCCO1. ON1 is negative edge triggered and internally pulled high
via a weak resistor.
Interrupt output/input; internally pulled low via a weak resistor during output;
level activated via strong high voltage for input.
Off control for VCCO1; edge-triggered active low.
VCCO2
Output
ON2/OFF2
Input
ON3/OFF3
Input
VCCO4
Output
ON4
Input
VCCO4 trigger; edge activated; active low.
SENSE
Input
Sense input sampled just prior to VCCO4 off; turns on VCCO1 if active; active
high.
MODE4
Input/Output
RXIN
Input
Serial I/O input; On control for VCCO1 when serial activity detected; edge activated.
RXOUT
Output
Serial I/O output; Echos incoming serial data from RXIN when VCCO1 is turned
on.
OSCEXT
Output
Oscillator Signal Output; Gated by internal comparator when BOOST is enabled. Continuous when BOOST is disabled.
022698 2/20
On/Off controls for VCCO2/VCCO3; level activated.
Momentarily switched VCC output.
Selects VCCO4 on time; level sensitive input/current source output.
DS1227
INPUT SUPPLY VOLTAGE
The Kickstarter is capable of operating either in a regulated step-up DC-to-DC conversion (boost) mode or in a
non-regulated supply voltage Pass-Through mode.
In boost mode, the Kickstarter is designed to provide a
regulated +5V output on the VCCO1, VCCO2, or VCCO3
voltage supply output pins from a +3V lithium source.
Figure 1 illustrates the standard configuration for use of
this mode. The BOOST pin should be tied low in order to
enable step-up DC-to-DC conversion. VDCI is used for
the DC power supply input and is tied through an inductor (270 µH typical) to a +3V lithium cell. VDCO is the
main DC output which is switched to the VCCO1, VCCO2,
and VCCO3 outputs. This pin requires a large capacitor
(typically 100 µF) to ground for the boost regulation low
pass output network. Further details of the boost voltage
regulator operation are given in the “Boost Mode Operation” section of this data sheet.
Figure 2 and Figure 3 illustrate the required configurations to select the supply voltage Pass-Through mode of
operation. In both of these configurations the BOOST
pin should be strapped directly to the VDCO pin. This
connection causes the BOOST pin to remain at a high
level at all times that a battery is connected. As a result,
the internal boost regulator will be disabled when kickstarting occurs. When a +5V supply is used as the input
DC power source, it should be directly connected to the
VDCO in parallel with a filter capacitor as shown in Figure
2. The VDCI input itself should be grounded in this configuration.
If a +6V supply is used, then it should be connected to
the VDCI pin. A filter capacitor should still be connected
to VDCO. The voltage on VDCO and subsequently on
VCCO1, VCCO2, and VCCO3 (when they are enabled following kickstarting) will be a diode drop below the VDCI
voltage.
In both the Boost and Pass-Through modes, the
DS1227 uses the voltage on VDCO as its own internal
supply.
DS1227 BOOST MODE CONFIGURATION Figure 1
DS1227
KICKSTARTER
270 uH (typ.)
VDCI
VCC02
+
+3V
–
.01 uF
Bypass
(typ.)
VCC01
VCC03
VDCO
100 uF
Filter
(typ.)
BOOST
GND
022698 3/20
DS1227
DS1227 +5V PASS-THROUGH MODE CONFIGURATION Figure 2
DS1227
KICKSTARTER
VDCI
VCC01
VCC02
VCC03
BOOST
VDCO
+
10 uF
(typ.)
+5
–
GND
DS1227 +6V PASS-THROUGH MODE CONFIGURATION Figure 3
DS1227
KICKSTARTER
VDCI
+
VCC01
VCC02
+6V
VCC03
–
BOOST
VDCO
10 uF
(typ.)
GND
KICKSTARTER OPERATION
A conceptual block diagram of the internal circuitry of
the DS1227 is illustrated in Figure 4 for reference. While
in an initial power down state, the DS1227 will sense activity from an external stimulus applied to one of three
input pins and kickstart system power by applying voltage from the input power source to the primary VCCO
output (VCCO1). Activity detected on any of the ON1,
RXIN, and SENSE pins initiates the kickstarting action.
022698 4/20
When kickstarting occurs and the DS1227 is configured
for boost operation, the on-chip, step-up DC-to-DC converter is started and the voltage on VDCO will be boosted
from its initial VBAT level to VDCON before VCCO1 is
turned on. If the DS1227 is configured for voltage
Pass-Through operation, then the DC-to-DC converter
will remain disabled and voltage on the VDCO line will be
switched to the VCCO1 pin immediately following the detection of an active transition on a stimulus input.
DS1227
Initially, when VCCO1 is off, the INT/ACK pin is collapsed
to ground. At the time that voltage is switched to the
VCCO1 output pin during kickstarting, the INT/ACK pin
will be latched such that it will remain in a low state. This
signals the microcontroller that a power on reset has occurred. The OFF1, ON2/OFF2, and ON3/OFF3 inputs
are all ignored until the microcontroller acknowledges
this power on reset condition. This acknowledgement is
performed via the same INT/ACK pin, which also performs the function of an interrupt acknowledge input.
This is made possible due to the fact that the pin has a
weak NMOS pulldown which forms a latch. When INT/
ACK is externally driven with a sufficiently strong high
signal (as described in the “Electrical Characteristics”
section) the state of the latch will be switched and as a
result the interrupt condition will be reset.
After the power on reset interrupt has been acknowledged and the DS1227 is in a power on condition, the
INT/ACK pin will be again taken low to signal the detection of active signalling on the ON1 or SENSE inputs.
Further activity on the RXIN input will not cause a subsequent interrupt condition. The INT/ACK can be returned to its high (reset) state again by externally driving
it with a sufficiently strong high signal.
The OFF1 input is used to turn off the VCCO1 output under software control. It is typically interfaced to the system microcontroller via a port pin configured as an output. As noted above, it is active only when VCCO1 is on
and INT/ACK has been set high.
STIMULUS INPUTS
ON1 is a simple TTL-level compatible input which is designed to detect a negative-going edge. VCCO1 is kickstarted whenever an active edge is detected on this pin.
The RXIN input can be used to initiate the kickstarting
action in response to the detection of incoming serial
data. In this configuration, the RXIN pin is interfaced to
an incoming serial data line, typically from an RS232
transceiver. RXOUT is the corresponding output and is
used to route the serial data to the microcontroller. RXIN
remains internally disconnected from RXOUT until
VCCO1 is powered on. At that time, the two lines are connected and serial data is passed straight through the device to the microcontroller.
The SENSE pin is intended to be connected to an external sensor circuit which is powered from VCCO4. This
circuit is then momentarily powered from the Kickstarter’s VCCO4 output in response to a negative going edge
applied to the ON4 input. VCCO4 will stay powered for an
amount of time determined by the circuitry on the
MODE4 pin. During the time that VCCO4 is on, the
SENSE pin has an internal pulldown device which is activated. SENSE is sampled just prior to the VCCO4 output being disconnected. If SENSE is externally driven
high (VIH) at this time, it kickstarts VCCO1 power. Any
time that VCCO4 power is off, the SENSE pin appears as
a high impedance to external circuitry.
The amount of time that VCCO4 is on is determined by
the configuration of the MODE4 pin. MODE4 is intended
to either be tied high (typically to VDCO) or tied to an external capacitor. The VCCO4 on time is thereby determined either by the amount of time between falling
edges on ON4 or by the value of the capacitor.
If the MODE4 pin is tied high at the time that ON4 is activated, then VCCO4 will remain on until the next falling
edge is detected on ON4. Figure 5 illustrates the timing
associated with this mode of operation. If the Kickstarter
is also configured for boost regulation and VCCO1,
VCCO2, and VCCO3 are turned off, the DC-DC converter
will be briefly enabled so that +5V will be supplied on
VCCO4 for the duration of the time that it is on.
The alternative MODE4 configuration is illustrated in
Figure 6A. As shown in the figure, it is recommended for
most applications that a large resistor also be connected between MODE4 and ground in addition to the
capacitor. For the configuration shown, the MODE4 pin
will be sensed low by the Kickstarter just following the
negative-going edge at ON4. Following this condition, a
constant current specified as IM4ON is supplied out of
the MODE4 pin. This will cause the voltage on MODE4
to rise linearly. VCCO4 will remain on until the voltage on
MODE4 reaches a threshold specified as VM4OFF (approximately 0.5 VDCO). At this time, VCCO4 will be shut
off. At the same time, the constant current source on the
MODE4 pin will be disconnected and an internal resistive element (specified as RM4DIS) will be connected between the MODE4 pin and ground. This internal resistive element along with any external resistance will
cause the voltage on the capacitor to decay exponentially until it reaches a threshold specified as VM4DIS (approximately 0.1 VDCO). When this condition is reached,
the internal resistive element will be disconnected, and
the MODE4 pin will appear as a high impedance until the
next active transition occurs on ON4. The external re-
022698 5/20
DS1227
sistor (if present) will then cause the voltage on MODE4
to further decay until it reaches ground or until the next
ON4 negative transition, whichever comes first.
When MODE4 is initially grounded as described above,
VCCO4 power is switched from the VDCO pin, regardless
of whether or not VCCO1, VCCO2, or VCCO3, are powered
on. This means that VCCO4 will be switched with the voltage present on VDCO, which could be from +3V to +5V
depending on the configuration, input battery voltage
used, and whether or not VCCO1, VCCO2, or VCCO3 are
switched on.
The above described sampling operation of VCCO4 and
SENSE in response to ON4 also takes place when a
kickstart has already occurred and VCCO1 is on. If
SENSE is found to be active in this condition, an interrupt will be signalled on the INT/ACK pin.
MICRO ENERGY MANAGEMENT
In addition to the kickstarting features described above,
the DS1227 allows sections of system circuitry to be individually powered up or down under command of the
microcontroller. This capability is referred to as the Micro Energy Management feature of the DS1227.
VCCO2 and VCCO3 are auxiliary power supply outputs
which may be switched on or off via the ON2/OFF2 and
ON3/OFF3 pins, respectively. The ON2/OFF2 and
ON3/OFF3 control pins are intended for connection to
two microcontroller’s port pins configured as outputs.
The corresponding VCCO output pins can then be turned
022698 6/20
on or off as desired under control of the system application software.
The ON2/OFF2 and ON3/OFF3 inputs are level activated. The corresponding VCCO output therefore turns
on when the on/off pin is high and off when it is low.
These inputs are active only if the VCCO1 output is on
and the INT/ACK output has been set to a high state signalling a power on reset condition.
When VCCO2 or VCCO3 are turned on, they will remain
on until the corresponding control input is taken low by
the software. This is true even if the OFF1 input is taken
to its active low state at the time that either ON2/OFF2,
ON3/OFF3, or both, are high.
Once OFF1 is activated, the current states of
ON2/OFF2 and ON3/OFF3 are internally latched and
further activity on these pins is ignored. If both of the corresponding outputs (VCCO2 and VCCO3) are turned off at
this time and boost operation has been selected, then
the internal oscillator is killed and the DC-to-DC converter will be shut down. If either VCCO2 and/or VCCO3 are
left switched on when OFF1 is activated, they will remain switched on even after VCCO1 has been turned off.
If the DS1227 has been configured for boost operation,
the DC-to-DC converter will remain operational during
the entire time that VCCO1 is turned off so that +5 volts
will continue to be supplied on either or both of these
output pins. These pins can be shut off only when kickstarting occurs once again and VCCO1 is switched on
and INT/ACK has been set high.
DS1203
DS1209
ON3/OFF3
ON2/OFF2
OFF1
ON1
RXIN
SENSE
VCC04
MODE4
ON 4
VDCO
OSCEXT
BOOST
VDCI
EVENT
TRIGGER
CIRCUITS
ONE
SHOT
Q
Q
CLR
D
DC-DC
CONVERTER
Q2
D2
G
Q1
D1
PWRON
HIENUF
VCC0 (+5V)
R
S Q
VCC03
VCC02
PWRON1
INT/ACK
VCC01
D/A
RAM
DS1283
LCD DISPLAY
A/D
DS5000FP
DS1227
DS1227 KICKSTARTER BLOCK DIAGRAM Figure 4
022698 7/20
DS1227
SENSE INPUT TIMING; MODE4 STRAPPED HIGH Figure 5
MODE4
ON4
tD4ON
tD4OFF
VCC04
SENSE
VCC01
MODE4 RC NETWORK CONNECTION Figure 6A
ON4
tD4ON
VCC04
tV4ON
MODE4
tM4OFF
tM4OIS
SENSE
VCC01
SENSE INPUT TIMING; MODE4 WITH RC NETWORK Figure 6B
DS1227
KICKSTARTER
MODE4
If I M4ON
R
C
t V4ON
022698 8/20
12 V DCO
:
R
12 C (I
V DCO
M4ON
)
DS1227
BOOST MODE OPERATION
The DS1227 Kickstarter incorporates all of the necessary control and power switching functions required for
its +3V to +5V step-up DC-to-DC converter. These functions include a bandgap reference, oscillator, voltage
comparator, catch diode and an N-channel MOSFET.
The only external components required are an output filter capacitor and a low cost inductor. The block diagram
shown in Figure 7 illustrates the DC-to-DC converter.
When kickstarting occurs from an initial powered down
state (i.e., VCCO1, VCCO2, and VCCO3 turned off), an internal start sequence is initiated within the DS1227.
During this sequence, the VCCO1 output remains shut
off and the BOOST pin is sampled in order to determine
if the DS1227 is configured for boost mode operation. If
BOOST is low, then boost mode operation is enabled
and the DC-to-DC converter is started.
The internal DC-to-DC converter is started by enabling
the on-chip 40 KHz oscillator. It then begins to build up
the voltage on the VDCO filter capacitor. Internal counter
logic insures that the DC-to-DC converter stays in start
mode for a minimum of six clock periods (nominally
150 µs @ 40 KHz). After this initial delay time, the VDCO
output is monitored by the internal Error Comparator as
it slews up to VDCON. As long as the VDCO voltage remains below the preset value, the Error Comparator will
be switched high and the internal 40 KHz oscillator will
be connected to the gate of the VDCI driver.
The VDCI driver is a large N-channel MOSFET with a
typical ON resistance of less than 4 Ohms and is capable of supplying a peak current of 450 mA. The output
device is turned on during each ON half-cycle generated by the internal square-wave oscillator, and is
turned off during each OFF half-cycle. During each ON
half-cycle, the current through the inductor rises linearly,
storing energy in the coil. When the output device is
turned off, the external inductor’s magnetic field collapses, and the voltage across the inductor reverses
sign. The voltage at VDCI then rises until the internal
diode is forward biased, delivering power to the VDCO
output. The converter is thereby powered from its own
VDCO output. This is often referred to as “bootstrapped”
operation, since the circuit figuratively “lifts” itself up. In
order to guarantee that the Kickstarter can bootstrap itself up to operating voltage, the VDCI voltage must be at
the minimum level of VDCISU as listed in the DC characteristics section of this data sheet.
When the voltage on VDCO rises to the VDCON threshold, the internal signal called “HIENUF” will be active
and the VCCO1 PMOS device is switched on. As noted
above, internal circuitry insures that this device will not
be switched on for a minimum of 6 clock cycles from the
time that the DC-to-DC converter is started. However,
since the recommended values for the external LC components result in a time constant which is much longer
than six cycles, the actual slew rate will in practice be
much longer than this delay time.
If loading of the VCCO outputs causes VDCO to drop below VDCOFF the DS1227 will deactivate HIENUF and
the VCCO1 PMOS device as well as the other VCCO
PMOS devices will be switched off. The VDCO voltage
will then be monitored for the VDCON trip point before reconnecting the load. As a result, the power control regulation loop could oscillate between these two states until
the VCCO1 node had sufficient charge to remain above
the VDCOFF threshold. To prevent this from occurring,
the value of the filter capacitor must be sufficiently large.
For large capacitive loads on VCCO1 the output may dip
below VDCOFF as a result of charge sharing and a larger
regulation capacitor at VDCO may be required. For large
resistive loads the inductance and capacitance values
may need to be adjusted using a smaller inductor value
and large capacitance. In order not to violate the peak
VDCI current it may be necessary to use the external oscillator OSCEXT to drive an additional switchmode
boost regulator, as shown in Figure 8.
Following the above described start sequence, normal
boost operation is performed by the converter. VDCO
output voltage is constantly monitored by the error comparator. When VDCO voltage drops below the preset value, the error comparator switches high and connects
the internal 40 KHz oscillator to the gate of the VDCI output driver. When the output voltage reaches the desired
level, the error comparator inhibits the VDCI output driver until the load on VCCO1 discharges the output filter capacitor to less than the desired output level.
INDUCTOR SELECTION
The available output current from the Kickstarter’s
on-chip DC-DC boost converter is a function of the input
voltage, external inductor value, output voltage and the
operating frequency. For most applications, the inductor
is the only design variable since the internal oscillator is
preset to a fixed value of 40 KHz. The proper inductor
must have the following characteristics:
022698 9/20
DS1227
1) the correct inductance value must be selected.
The energy in the inductor is:
2) the inductor must be able to handle the required peak
currents.
EL 3) the inductor must have acceptable series resistance
and must not saturate.
When the internal N-channel MOSFET turns on, the
current through the inductor rises linearly since:
di
V
where L is the inductance value
dt
L
At the end of the on-time, tON, the peak current, IPK is:
I PK V t ON
L
where : t ON L I PK
2
2
At maximum load this cycle is repeated f0 (typically 40
KHz) times per second, and the power transferred
through the coil is PL = f0 x EL. Since the coil only supplies the voltage above the input voltage:
I OUT PL
V OUT V IN
1
2f O
DC-DC CONVERTER Figure 7
DC TO DC CONVERTER
VDCO
BOOST
VDCI
CATCH
DIODE
ERROR
COMPARATOR
EXTERNAL
PINS
–
VDCI
DRIVER
D Q
+
Q
CLR
LOAD
COMPARATOR
+
–
OSCEXT
8 CLK DELAY
40 KHZ
OSCILLATOR
PWRON*
(INTERNAL
SIGNAL)
022698 10/20
VCCO
M
U
X
BANDGAP
REFERENCE
INTERNAL
SIGNALS
HIENUF
DS1227
AUXILIARY BOOST SUPPLY CONFIGURATION Figure 8
100 µH (typ.)
VCCOAUX
1N5418
DS1227
KICKSTARTER
OSCEXT
270 µH (typ.)
VDCI
+
+3V
–
VCC01
VCC02
VCC03
VDCO
200 µF (typ.)
BOOST
GND
The DC-DC converter’s output current is provided both
by the inductor and directly from the battery. If the load
draws less than the maximum current, the VDCI n-channel MOSFET is turned on only often enough to keep the
output voltage at the desired level.
If the selected inductor has too high a value, the DS1227
will not be able to deliver the desired output power, even
with the MOSFET turned on for every oscillator cycle.
The available output power can be increased by either
raising the input voltage or lowering the inductance.
This causes the current to rise at a faster rate, and results in a higher peak current at the end of each cycle.
The available output power increases since it is proportional to the square of the peak inductor current. The
maximum inductance therefore is:
L MAX V IN 2
8 fO PL
since : P L where:
IOUT
=
IOUT1 + IOUT2 + IOUT3 + IOUT4
If the inductance value is too low, the current at VDCI
may rise above the maximum rating. The minimum allowed inductor value is expressed by:
L MIN V IN
(I
450 mA)
2 f O I MAX MAX
TYPES OF INDUCTORS
The following is a brief discussion of various types of inductors which may be typically used with the DS1227
Kickstarter to facilitate boost mode operation. Table 1
lists some typical manufacturers of these types of inductors. Table 2 summarizes performance of the circuit for
various inductors.
Molded Inductors
L I PK2 f O
2
and : I PK
V IN
f L
2 O
The required output power must include what is dissipated in the forward drop of the catch diode and each of
the VCCO1, VCCO2, and VCCO3 pass transistors. This
can be expressed as follows:
POUT = VF IOUT + (IOUT12 RON1 + IOUT22 RON2 +
IOUT32 RON3 + IOUT42 RON4) + VOUT IOUT
These are cylindrically wound coils which look similar to
1-watt resistors. They have the advantages of low cost
and ease of handling, but have higher resistance, higher
losses, and lower power handling capability than other
types of inductors.
Potted Toroidal Inductors
A typical 1 mH, 0.82 ohm potted toroidal inductor (Dale
TE-3Q4TA) is 0.685 in diameter by 0.385 high and
022698 11/20
DS1227
mounts directly onto a printed circuit board by its leads.
Such devices offer high efficiency and mounting ease,
but at a somewhat higher cost than molded inductors.
Ferrite Cores (Pot Cores)
Pot cores are very popular as switch-mode power supply applications since they offer high performance and
ease of design. The coils are generally wound on a plastic bobbin, which is then placed between two pot core
sections. A simple clip to hold the core sections together
completes the inductor. Smaller pot cores mount directly onto printed circuit boards via the bobbin terminals.
Cores come in a wide variety of sizes often with the center posts ground down to provide an air gap. The gap
prevents saturation while accurately defining the inductance per turn squared.
Pot cores are suitable for all DC-DC converters, but are
usually used in the higher power applications. They are
also useful for experimentation since it is easy to wind
coils onto the plastic bobbins.
Toroidal Cores
In volume production, the toroidal core offers high performance, low size and weight, and low cost. They are,
however, slightly more difficult for prototyping, in that
manually winding turns onto a toroid is more tedious
than on the plastic bobbins used with pot cores. Toroids
are more efficient for a given size since the flux is more
evenly distributed than in a pot core, where the effective
core area differs between the post, side, top, and bottom.
Since it is difficult to gap a toroid, manufacturers produce toroids using a mixture of ferromagnetic powder
(typically iron or Mo-Permalloy powder) and a binder.
The permeability is controlled by varying the amount of
binder, which changes the effective gap between the
ferromagnetic particles. Mo-Permally powder (MFP)
cores have lower losses and are recommended for the
highest efficiency, while iron powder cores are lower
cost.
COIL AND CORE MANUFACTURERS Table 1
TYPE
TYPICAL
MANUFACTURER
PART #
DESCRIPTION
Molded
Dale
1HA-104
500 µH, 0.5 ohms
”
Cadell-Burns
7070-29
220 µH, 0.55 ohms
”
Gowanda
1B253
250 µH, 0.44 ohms
”
Nytronics
WEE-470
470 µH, 10 ohms
”
TRW
LL-500
500 µH, 0.75 ohms
Potted Toroidal
Dale
TE-3Q4TA
1 mH, 0.82 ohms
”
Gowanda
050AT1003
100 µH, 0.05 ohms
”
TRW
MH-1
600 µH, 1.9 ohms
”
Torotel Prod.
PT 53-18
500 uH, 5 ohms
Toroidal Core
Allen Bradley
T0451S100A
500 nH/T2
”
Siemans
B64290-K38-X38
4 µH/T2
”
Magnetics
555130
53 nH/T2
Ferrite Core
Stackpole
57-3215
14 mm x 8 mm
”
Magnetics
G-41408-25
14 x 8, 250 nH/T2
Note:
This list does not constitute an endorsement by Dallas Semiconductor and is not intended to be a
comprehensive list of all manufacturers of these components.
022698 12/20
DS1227
INDUCTOR SELECTION FOR COMMON DESIGNS Table 2
VIN
VDCO
IOUT
EFF.
(V)
(mA)
(%)
PART #
uH
Ohms
2
5
5
78
CB 6860-21
470
0.4
2
5
10
74
G 1B253
250
0.44
2
5
15
61
G 1B103
100
0.25
3
5
25
82
CB 6860-21
470
0.4
3
5
40
75
CB 7070-29
220
0.55
(V)
Note:
CB = Cadell-Burns, NY (516) - 746 -2310
G = Gowanda Electronics Corp., NY (716) - 532-2234
Other manufacturers listed in Table 1.
OUTPUT FILTER CAPACITOR
In boost regulation mode, the DS1227’s output voltage
ripple on VDCO has two components, with approximately 90o phase difference between them. One component
is created by the change in the capacitor’s stored
charge with each output pulse. The other ripple component is the product of the capacitor’s charge/discharge
current and its ESR (Effective Series Resistance). With
low cost aluminum electrolytic capacitors, the ESR produced ripple is generally larger than that caused by the
change in charge.
V ESR I PK x ESR V IN
x ESR (Volts p p)
2Lf O
Where VIN is the coil input voltage, L is its inductance, f
is the oscillator frequency, and ESR is the equivalent series resistance of the filter capacitor.
The output ripple resulting from the change in charge on
the filter capacitor is:
V dQ t DIS x I peak
Q
where, Q 2
C
and, I peak V dQ INDUCTOR
High quality aluminum or tantalum filter capacitors will
minimize output ripple, even if smaller capacitance values are used. Best results at reasonable cost are typically achieved in the 100 to 500 µF range, in parallel with
a 0.1 µF ceramic capacitor.
OSCEXT FUNCTIONS
The OSCEXT pin is connected to the internal 40 KHz
oscillator (nominal frequency). When Boost mode is enabled (BOOST = 0) and the DC-to-DC converter is running, OSCEXT is active at the same time whenever the
error comparator is switched high, i.e., whenever the internal oscillator is enabled to the gate of the VDCI driver.
In this configuration it may be used to drive an auxiliary
switch mode boost regulator as shown in Figure 8. In
this circuit, OSCEXT drives an external NMOS switch
with its drain pin connected to an additional inductor and
filter capacitor as well as an external catch diode. The
amount of supply current which can be realized at the
+5V output is determined by the power ratings of the external components. Through proper selection of the
these components, increased supply current can be
realized than is possible using the Kickstarter’s internal
VDCI driver and catch diode.
t CHG x V IN
L
V IN x t CHG x t DIS
2LC
Where tCHG and tDIS are the charge and discharge
times for the inductor 1/2 fO can be used for nominal calculations).
When the Pass-Through mode is enabled (BOOST = 1)
and at least one of the VCCO outputs is switched on, the
OSCEXT pin will be continuously driven with the 40 KHz
frequency. In this configuration this pin could potentially
be used to generated negative or doubled voltages as
shown in Figure 9.
022698 13/20
DS1227
VOLTAGE INVERTOR AND DOUBLER CONFIGURATIONS Figure 9
DS1227
KICKSTARTER
OSCEXT
+
10 µF
+
10 µF
VOSCEXT = -(VDCO - 2VF)
1N4148
1N418
DS1227
KICKSTARTER
1N4148
1N4148
VDCO
VOSCEXT = 2(VDCO - VF)
+
OSCEXT
NOTE: VF = FORWARD 1N418 DIODE VOLTAGE
APPLICATION BRIEF
The schematic shown in Figure 10 illustrates a typical
application of the DS1227 Kickstarter in a microcontroller-based, battery powered system. Together with the
Kickstarter, the system incorporates a DS5000FP Soft
Microcontroller, a DS1283 Watchdog Timekeeper, and
a DS1275 Line Powered RS232 Transceiver. Although
the system is not designed to serve a specific application, this chip set could serve the majority of requirements for many types of hand-held instruments.
Using the illustrated configuration provides the following
major features:
• Permanently powered operation from a +3V
source for many applications
• Data and event logging with time stamp and
date
• Reprogrammable through RS232
serial interface
• Buttonless (autonomous) operation for many
tasks
COMPONENT DESCRIPTION
The DS5000FP is an 8-bit microcontroller which is
instruction set-compatible with the industry standard
022698 14/20
8051. It provides an embedded interface to 32 Kbytes of
nonvolatile static RAM which can be dynamically partitioned for program and data storage, and may be loaded
at any time via the on-chip serial port. With proper selection of RAM and the backup lithium source, nonvolatile
storage can be maintained for over 10 years in the absence of VCC. The DS5000FP offers the standard low
power operating and standby modes (i.e., Idle, Stop).
More importantly, sophisticated crashproof circuitry in
conjunction with the lithium energy source allows it to retain its entire operating state for the duration of a power
outage without drawing current from its VCC line.
Timekeeping is provided by the DS1283 Watchdog
Timekeeper. Incorporating a self-contained clock and
calendar, the DS1283 tracks hundredths of seconds,
seconds, minutes, hours, days, date of the month,
month, and years. When its chip enable is inactive (no
read or write), the DS1283 consumes extremely low
current, typically 500 nA. Two alarm functions are provided: a time-of-day Alarm, and a watchdog alarm. The
time-of-day Alarm can generate an interrupt pulse up to
one week in advance of the current time. The watchdog
alarm can produce an interrupt at regular intervals ranging from .01 seconds to 99.99 seconds. Both alarms
function when the part is operating in low power standby
mode.
DS1227
The DS1275 Line Powered RS232 Transceiver allows
the instrument to communicate with the RS232 port on a
host computer (e.g., COM port on an IBM PC). It operates from a +5V supply and draws no power from the
instrument’s main energy source to create negative
voltages. Instead, it steals power from the incoming
RXD line to generate the negative voltages needed during transmission.
INSTRUMENT OPERATION
A common requirement of instruments is event logging
with time stamp and date. The Dallas chip set provides
this capability using the DS5000 and DS1283. The
DS1283 interfaces directly to the DS5000FP embedded
bus, and may be accessed by CE2. In this way, valuable
port pins are conserved. Events can be recorded by the
microcontroller and logged in RAM with the date and
time. In the absence of VCC, the data will be retained in
RAM by the backup lithium cell. The same energy cell
provides backup to the DS1283, so that timekeeping is
maintained in the absence of a primary energy source.
Therefore, events may be time stamped and dated with
confidence that the correct time has been maintained.
Backup lithium current is managed by the DS5000FP
and is distributed from the VCCO line in the absence of
VCC.
PERMANENTLY POWERED OPERATION
In order to achieve permanently powered operation,
Dallas Semiconductor uses several techniques which
conserve the life of a primary energy source. First, the
illustrated chip set operates at extremely low power.
These components are also capable of very low power
data retention. Second, the crashproof circuitry of the
DS5000 allows VCC to be removed and restored without
disruption. This allows the energy management circuits
of the Kickstarter to power down the microcontroller during periods when it is unused. Since the DS1227 can
monitor external events and wakeup the DS5000 as
necessary, the microcontroller and other circuitry may
remain in low power data retention mode until needed.
The DS5000, RAM, and DS1283 will be backed up via
the button cell as show in Figure 1. Finally, the Kickstarter allows software-controlled powering of auxiliary circuits when tasks require them.
Low operating power is a basic requirement of batteryoperated systems. The illustrated Dallas chip set can
perform most instrument functions using minimal power. Using a 3.57 MHz crystal, the circuit in Figure 1 will
draw approximately 8 mA during microcontroller operation. When the Kickstarter turns off the DS5000, the circuit draws approximately 5 µA from the primary energy
source. If a similar configuration were created with an
ordinary CMOS microcontroller in stop mode, the current could be as high as 55 µA. Idle mode operation
would consume approximately 3 mA, which would excessively drain a primary power source over extended
periods. The Dallas low power chip set provides a tento-one improvement over previously available alternatives.
Achieving the lowest power instrument requires the
DS1227 Kickstarter. Using the Kickstarter, low power
operation is achieved by powering down the microcontroller. When this occurs, the DS5000 effectively consumes zero power. RAM and key registers are backed
by the lithium button cell, with no power draw from VCC.
When a task must be performed, the Kickstarter powers
up the DS5000 to execute a function and powers it down
when the function is complete (under software direction). The period for which power remains on is minimized in this way. Since most tasks require minimal processing time with long periods of waiting, the instrument
may remain in a low power data retention mode for the
majority of time. Therefore, even if an operator interface
is necessary, the microcontroller can remain on for milliseconds (or microseconds) to perform a task, and remain off for the seconds between operations.
The ability to react to external stimuli allows the instrument to operate autonomously for many applications.
Fundamental to this operation is the kickstart caused by
external stimuli. The following section describes the operation of the Kickstarter with respect to four different
stimuli.
KICKSTARTING OPERATION
The DS1227 receives primary power from a +3V lithium
battery. Prior to a kickstart, battery voltage is present on
VDCO, which is the main voltage output. When the system receives a kickstart stimulus, an on-chip boost regulator raises VDCO to +5V. Upon completion of power
up, +5V is switched to the DS5000 on VCC01. Prior to
kickstart, no power was supplied to this line.
022698 15/20
022698 16/20
+
75
77
79
1
5
7
9
11
31
29
27
25
21
19
17
15
68
70
73
34
DS5000FP
ECE1
ECE2
ER/W
VCC0
VLI
VCC
VCC
GND
GND
XTAL2
XTAL1
+3V Lithium
(button cell)
16
8
18
80
76
4
6
20
24
26
28
30
33
35
37
71
69
67
65
61
59
57
55
P2.7
P2.6
P2.5
P2.4
P2.3
P2.2
P2.1
P2.0
P3.7
P3.6
P3.5
P3.4
P3.2
P3.1
P3.0
P0.7
P0.6
P0.5
P0.4
P0.3
P0.2
P0.1
P0.0
P1.7
P1.6
P1.5
P1.4
P1.3
P1.2
P1.1
P1.0
PSEN
ALE
EA
RESET
100uF
TO AUXILIARY
CIRCUITS POWER
1
2
3
4
5
6
7
8
9
10
DS1227
EA14
EA13
EA12
EA11
EA10
EA9
EA8
EA7
EA6
EA5
EA4
EA3
EA2
EA1
EA0
ED7
ED6
ED5
ED4
ED3
ED2
ED1
ED0
A13
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
+3V
LITHIUM (Primary Power
BATTERY Source)
VCC02
VCC03
VCC01
PWRON
VDC0
VDC1
GND
ON/OFF3
OFF1
ON/OFF2
VCC04
MODE4
SENSE
INT/ACK
OSCEXT
BOOST
ON1
ON4
RXIN
RXOUT
32Kx8
SRAM
20
19
18
17
16
15
14
13
12
11
VCC
WE
A14
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
.001uF
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DS1275
DS1283
LED
5K
DOUT 1
VDRV 2
DIN 3
GND
4
44OK
INTA
X1
X2
NC
32KHZ A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
PHOTO
DIODE
1M
28
27
26
25
24
23
22
21
20
19
18
17
16
15
VCC
WE
INTB
VBAT
RCLR
SQW
OE
INTP
CE
DQ7
DQ6
DQ5
DQ4
DQ3
VCC
8
RXIN
7
NC
6
TXOUT
5
4.7K
TO RS232
DS1227
TYPICAL APPLICATION OF DS1227 KICKSTARTER Figure 10
DS1227
The schematic in Figure 1 demonstrates four kickstart
stimuli. They are real time clock alarm, RS232 incoming
data, a sensor input, and a user switch. During the low
power standby prior to kickstart, VCCO from the DS5000
provides battery power to the RAM and real time clock
from the button cell. VDCO supplies the RS232 transceiver. While operating on battery power, the RTC can
still issue alarms. If a time of day alarm is programmed,
INTA will be taken low by the RTC when the alarm occurs. Th is is connected to ON1, and issues a Kickstart.
Incoming RS232 activity will allow the transceiver to
Kickstart the DS1227. Following the initial interrupt, all
additional RS232 data is passed through the RXIN/
RXOUT pins of the DS1227 to the DS5000 without further action. In this way, the instrument can collect a table
of data and dump it to a PC for analysis when necessary.
Since the instrument will kickstart when it detects
RS232 communication, it is unnecessary for an operator to take further action. Enough time should be allowed
for the DS5000 to complete a power-on reset before
sending meaningful data.
Two additional methods of kickstarting are illustrated.
One method involves the use of a sampled sensor. A periodic pulse (the watchdog alarm) from the DS1283
causes VCC04 to be applied to the LED. For example,
this might occur every 250 ms. It remains on for the time
it takes to charge the capacitor on Mode4 to 1/2 VDCO
(1.5V). In this example, the on period is approximately
75 µsec. Just prior to removing VCC04, the sense line is
sampled. If the LED light path to the photodiode is
blocked, the sense line will be high and the system will
be kickstarted. If the light path is clear, the sense line will
be low, and nothing will happen. This facilitates checking for the presence of an ID card in a reader. In the other
method a user switch, which is momentarily closed, will
start the system. This is tied to ON1 in a wired-OR configuration. All of the above kickstart stimuli cause the
boost regulator to raise VDCO and turn on VCC01. In
summary, the four kickstart stimuli are:
1) Time of Day Alarm - INTA goes low and Kickstarts
VCC01.
4) A user switch momentarily pulls ON1 low and kick
starts.
Although the user switch is easily implemented, it may
be unnecessary. By allowing the instrument to power up
and determine the cause of the Kickstart, it is possible to
achieve buttonless operation in many applications. Automatic response allows the instrument to function autonomously and save power by turning off unused circuits.
Once the DS5000 receives power, it must read the INT/
ACK line (tied to INT0). A power-on condition causes
this signal to be low. The DS5000 port pin should then
acknowledge power up by driving this line high. This
recognizes the interrupt and enables the kickstarter for
further activity. The DS5000 may now turn on auxiliary
loads VCC02 and VCC03 using ON/OFF 2 and 3 (tied to
any port pins). These auxiliary supplies may supply circuits which are not always necessary (e.g. an A/D converter). Peripheral circuits remain powered down until
needed. After an operation is complete, the DS5000 can
turn off the auxiliary circuits. When processing of a task
is complete, it may turn itself off using OFF1. An application may require that an auxiliary circuit remain on when
the microcontroller is off. This might occur with an LCD
display or dual slope A/D converter. Since the dual slope
A/D takes a relatively long period to convert (40-50 mS),
the microcontroller may be powered down while waiting.
Since the INT/ACK line is tied to INT0, additional kickstart stimuli which occur while VCC01 is on will cause
the DS5000 to receive an interrupt. This allows the
DS5000 to take action for specific conditions.
Precautions against excessive current drain are taken
in this application. For example, the data input to the
DS1275 RS232 transceiver is tri-stated when VCC01 is
off. This is necessary to prevent a high signal from driving the RS232 bus and consuming power while the
DS5000 is off. Similar precautions should be taken by
the user in designing systems with switched power supplies.
2) RS232 Activity - Powers up VCC01 and routes all
RS232 straight through to the DS5000.
3) INTB goes low periodically, VCC04 turns on, and the
sense line is sampled. If high, a kickstart occurs. If
low, no action.
022698 17/20
DS1227
ABSOLUTE MAXIMUM RATINGS*
Input Voltage on any Pin Relative to Ground
VDCI Peak Input Current
Power Dissipation
Plastic DIP (derate 7.41 mW/oC above +50oC)
Small Outline (derate 12.5 mW/oC above +50oC)
Operating Temperature
Storage Temperature
Lead Soldering Temperature
-0.3 to 7.0V
450 mA
- 555 mW
- 937 mW
–40°C to +85°C
-55°C to +125°C
260°C for 10 seconds
* This is a stress rating only and functional operation of the device at these or any other conditions above those
indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods of time may affect reliability.
ELECTRICAL CHARACTERISTICS
(tA = –40°C to +85°C)
PARAMETER
SYMBOL
MIN
Startup Voltage
VDCISU
1.8
VDCO Voltage Threshold for
VCCO Turn-ON
VDCON
4.20
VDCO Voltage Threshold for
VCCO Turn-OFF
VDCOFF
TYP
4.30
MAX
UNITS
NOTES
V
1
4.62
V
4.00
V
3.0
1.0
mA
mA
Operating Supply Current
(BOOST=0)
(BOOST=1)
ICC
Standby Supply
ISB
200
nA
VCCO1 DC Source Current
(VCCO1 = VDCO -0.25V)
ICCO1
100
mA
2, 7
VCCO2, VCCO4
DC Source Current
(VCCO2, VCCO4 = VDCO - 0.25V)
ICCO2
ICCO4
50
mA
2, 7
VCCO3 Source
Current (VCCO3 = VDCO - 0.25V)
ICCO3
10
mA
2, 7
VCCO1, VCCO2, VCCO3, VCCO4
Voltage
VOUTB
4.75
5.25
V
1, 4
VCCO1, VCCO2, VCCO3, VCCO4
Voltage
VOUTP
VDCO
-0.25
V
2
VCCO4 Voltage
VOUT4
VDCO
-0.25
V
VCCO1 ON Resistance
VCCO2, VCCO4 ON Resistance
VCCO3 ON Resistance
Efficiency
022698 18/20
1.5
0.5
5.00
RVCCO1
2.5
Ohms
RVCCO2,4
5.0
Ohms
RVCCO3
25
Ohms
80
%
4
2
1, 8
DS1227
PARAMETER
Line Regulation
+0.5VCCO < +VS < VCCO
SYMBOL
MIN
TYP
VCCO
MAX
UNITS
NOTES
0.4
%
1
Oscillator Frequency
40
KHz
Oscillator Duty Cycle
50
%
OSCEXT ON Resistance
ROSCEXT
50
75
Ohms
VDCI Driver ON Resistance
(@ IVDCI = 100 mA)
RVDCION
6
14
Ohms
1
IVDCIL
30
µA
1
VF
1.0
V
0.45
V
VDCI Driver OFF Leakage Current
(tA = 25o C)
Catch Diode Forward Voltage
Output Low Voltage,
(OSCEXT, PWRON1)
IOL = 1.6 mA
VOL
Output High Voltage
(OSCEXT, PWRON1)
IOH = -80 µA
VOH
2.4
Input Low Current
(INT, ON2/OFF2,
ON3/OFF3, ON4, BOOST)
IIL1
-1.0
Input Low Current
(ON1, RXIN)
IIL2
-50
µA
Output High Current
(PWRON1)
IOH
-400
µA
Output Low Current (PWRON1)
IOL
2.0
mA
RXIN Current
(VRXIN - VRXOUT < 500 mV)
IRXIN
10
mA
INT/ACK Input
Transition Current
IACKT
+ 2.0
mA
5
INT/ACK Input Leakage Current
0.0 < VIN < 0.1, or VDCO
- 0.1 < VIN < VDCO
IACKL
+ 200
µA
5
SENSE Resistance (VCCO4 ON)
MODE4 Source
Current (MODE4 = 0
when ON4 goes from 1 to 0)
V
1.0
250
IM4ON
10
45
µA
6
KOhms
100
µA
KOhms
MODE4 Source
Current Shutoff Voltage
VM4OFF
0.5VDCO
MODE4 Discharge Resistance
(Following current
source shutoff)
RM4DIS
2
MODE4 Discharge
Resistance Shutoff Voltage
VM4DIS
0.1VDCO
022698 19/20
DS1227
NOTES:
1. Applicable only when Boost mode operation is in effect.
2. Applicable only when Pass Through mode operation is in effect.
3. Valid when 2.5V < VDCO < 5.0V.
4. Measured with Boost Mode operation in effect; ICCO1 = ICCO2 = ICCO3 = ICCO4 = 0. This value represents the
amount of current drawn by the DS1227 itself during and does not include current supplied on the ICCO outputs nor does if boost operator includes inefficiencies of DC-to-DC conversion.
5. Input transition current on the INT/ACK pin is specified to indicate the amount of current required to switch the
pin from a high to a low or from a low to a high condition. Once the pin has switched states, then the leakage
current specification is applicable.
6. ON1 and RXIN have internal weak p-channel pull-up devices.
7. When BOOST operation is in effect, the total combined current supplied out of VCCO1, VCCO2, VCCO3, and
VCCO4 is limited by the VDCI peak current.
8. Actual efficiency is dependent on external discrete component characteristics.
9. Battery replacement in the boost mode requires the discharge of the capacitor attached to VDCO (pin 5). The
following, or similar, circuit is recommended (see Figure 11).
BATTERY DISCHARGE CIRCUIT Figure 11
BATTERY CHANGE
DETECTOR
TO BATTERY
VDCO (PIN 5)
RB400D
2N7002
+
100 µF
4M
TC7SU04F
022698 20/20