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PDF MAX847 Data sheet ( Hoja de datos )
| Número de pieza | MAX847 | |
| Descripción | 1-Cell / Step-Up Two-Way Pager System IC | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-1349; Rev 1a; 10/98
EVFAOLLULAOTWIOSNDKAITTAMSAHNEUEATL
1-Cell, Step-Up
Two-Way Pager System IC
________________General Description
The MAX847 is a complete power-supply and monitor-
ing system for two-way pagers or other low-power digi-
tal communications devices. It requires few external
components. Included on-chip are:
• A 1-cell input, 80mA output, synchronous-rectified
boost DC-DC regulator with a digitally controlled
+1.8V to +4.9V output
• Three low-noise linear-regulator outputs
• Three DAC-controlled comparators for software-
driven 3-channel A/D conversion
• SPI™-compatible serial interface
• Reset and low-battery (LBO) warning outputs
• Charger for NiCd, NiMH, lithium battery, or storage
capacitor for RF PA power or system backup
• Two 1.8Ω (typical) serial-controlled open-drain
MOSFET switches
An evaluation kit for the MAX847 (MAX847EVKIT) is
available to aid in design and prototyping.
Pin Configuration appears at end of data sheet.
____________________________Features
o 80mA Output from 1 Cell at 90% Efficiency
o 13µA Idle Mode™ (coast) Current
o Selectable Low-Noise PWM or Low-Current
Operation
o PWM Operating Frequency Synchronized to
Seven Times an External Clock Source
o Operates at 270kHz with No External Clock
o Automatic Backup-Battery Switchover
Ordering Information
PART
MAX847EEI
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
28 QSOP
________________________Applications
Two-Way Pagers
GPS Receivers
1-Cell Powered Hand-Held Equipment
____________________________________________________Typical Operating Circuit
INPUT
SINGLE AA
ALKALINE BATTERY
0.8V TO 1.8V
LOW-BATTERY
IN/OUT
RESET
IN/OUT
SERIAL
I/O
1.8Ω
DRIVERS
RUN
COAST
A/D INPUT
OPTIONAL
BATT
LBI LX1
LBO OUT
RSIN
RSO PGND
CS
SCL
SDI
SDO
DR1
DR2
DR2IN
DRGND
MAX847
REG2IN
OFS
REG2
REG1
RUN
REG3
CH0
SYNC FILT
REF AGND NICD
OUTPUT 2
2.85V ANALOG
OUTPUT 1
3V LOGIC
OUTPUT 3
1V RECEIVER
TO RF PA
NiCd BATTERY STACK
OR
STORAGE CAPACITOR
Idle Mode is a trademark of Maxim Integrated Products. SPI is a trademark of Motorola, Inc.
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
1 page  
1-Cell, Step-Up
Two-Way Pager System IC
ELECTRICAL CHARACTERISTICS (continued)
(OUT = 3.0V, BATT = 1.2V, NICD = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
CH2 Input Hysteresis (Note 15)
1 2 4 mV
CH0 Input Current
CH0 = 0.2V to 1.27V
-100
100 nA
CH Comparator Response Time
(Note 15)
10mV overdrive
0.6 1.0 µs
Note 1: Specifications to -40°C are guaranteed by design, not production tested.
Note 2: This is not a tested parameter, since the IC is powered from OUT, not BATT. The only limitation in the BATT range is the
inability to generate more than 5 times, or less than 1.15 times the BATT voltage at OUT. This is due to PWM controller
duty-cycle limitations in Run Mode.
Note 3: Minimum start-up voltage is tested by determining when the LX pins can draw at least 50mA for 1µs (min) at a 50kHz (min)
repetition rate. This guarantees that the IC will deliver at least 200µA at the OUT pin.
Note 4: This supply current is drawn from the OUT pin. Current drain from the battery depends on voltages at BATT and OUT and
on the DC-to-DC converter’s efficiency.
Note 5: Current into BATT pin in addition to the supply current at OUT. This current is roughly constant from Coast to Run Mode.
Note 6: Current into NICD pin when NICD isn’t being charged and isn’t regulating OUT.
Note 7: Current into NICD pin when NICD is regulating OUT. Doesn’t include current drawn from OUT by the rest of the circuit.
Measured by setting the OUT regulation point to 2.8V and holding OUT at 3.0V.
Note 8: Current into NICD pin when BATT and OUT are both at 0V. This test guarantees that NICD won’t draw significant current
when the main battery is removed and backup is not activated.
Note 9: Serial-interface timing specifications are not tested and are provided for design guidance only. Serial-interface functionali-
ty is tested by clocking data in at 5MHz with a 50% duty-cycle clock and checking for proper operation. With OUT set
below 2.5V, the serial-interface clock frequency should be reduced to 1MHz to ensure proper operation.
Note 10: This specification is not directly tested but is guaranteed by correlation to LX on-resistance and current-limit tests.
Note 11: Measured by using the internal feedback network and Coast-Mode error comparator to regulate OUT. Doesn’t include
ripple voltage due to inductor currents.
Note 12: Measured by using the internal feedback network and Run-Mode error comparator to regulate OUT. Doesn’t include ripple
voltage due to inductor currents.
Note 13: Uses the OUT measurement techniques described for the OUT Error, Coast Mode, and OUT Error Run Mode specifications.
Note 14: PLL acquisition characteristics depend on the impedance at the FILT pin. The specification is not tested and is provided
for design guidance only.
Note 15: The limits in this specification are not guaranteed and are provided for design guidance only.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(RUN MODE, VOUT = 3.0V)
100
90
EFFICIENCY vs. LOAD CURRENT
(COAST MODE, VOUT = 3.0V)
100
VIN = 2.0V
VIN = 1.5V
90
EFFICIENCY vs. LOAD CURRENT
(COAST MODE, VOUT = 2.4V)
100
90 VIN = 2.0V VIN = 1.5V
80
VIN = 0.8V
80
VIN = 1.2V
80
70 VIN = 1.0V
70 VIN = 1.0V
VIN = 1.2V
VIN = 0.8V
60 60
VIN = 2.0V
50
VIN = 1.5V
50
70 VIN = 1.0V VIN = 1.2V
60 VIN = 0.8V
50
40
1
10 100
LOAD CURRENT (mA)
40
1000 0.1
1 10 100
LOAD CURRENT (mA)
1000
40
0.1
1 10 100
LOAD CURRENT (mA)
1000
_______________________________________________________________________________________ 5
5 Page 
1-Cell, Step-Up
Two-Way Pager System IC
Table 1. Run and Coast Mode Start-Up Requirements
SYNC OPERATION
CIRCUIT CONNECTION
No SYNC clock is used.
1) Connect REF to FILT
2) Remove R7, C9, and C10
On initial power-up, system can supply
SYNC clock to MAX847 when REG1 is
greater than 1.5V.
Use standard Figure 2 circuit
On initial power-up, system can supply
SYNC clock to MAX847 before, or
concurrent with, RSO going high.
On start-up, system does not supply
SYNC clock to MAX847 until after RSO
goes high.
Add Q1 as shown in Figure 3
Use standard Figure 2 circuit
START-UP MODE CAPABILITY
Can start in either Coast or Run Mode
by tying RUN pin appropriately. In Run
Mode the DC-DC converter operates at
270kHz.
Can start in either Coast or Run Mode
by tying RUN pin appropriately. In Run
Mode the DC-DC converter operates at
7fSYNC once the SYNC clock is applied.
Can start in either Coast or Run Mode
by tying RUN pin appropriately. In Run
Mode the DC-DC converter operates at
7fSYNC once the SYNC clock is applied.
Must start in Coast Mode. Run Mode may
then be started by the system after start-up.
The comparison threshold voltages for each channel
are described in the following equations:
VTH(CH0: pin 9) = D · 10mV
VTH (CH1: NICD) = D · 40mV
VTH(CH2: BATT) = D · 10mV
where D is the decimal equivalent of the binary code
DAC0–DAC6 (Table 2). DAC0 is the LSB. A DAC code
of 1111111 equates to D = 127. When all zeros are pro-
grammed, the CH DAC and CH_ comparators turn off.
CH0, CH1, and CH2 comparison results reside in the
three MSB locations of the output serial data (Table 5).
The CH_ OUT data is delayed by one read cycle. In
other words, each CH_ OUT bit is the result of the com-
parison made against the CH DAC voltage pro-
grammed during the previous serial-write operation.
An analog-to-digital (A/D) conversion can be performed
on a channel by using the system software to step
through a successive-approximation routine or, if the
input is partially known, by setting the CH DAC to a
voltage near the estimated point and checking succes-
sive CH_ OUT bits.
A faster A/D shortcut can be used for battery measure-
ments when the goal is a “go, no go” determination. For
this type of test, the CH DAC can simply be set to the
desired limit, and CH_ OUT supplies the result on the
next serial-write operation. One instance in which this
shortcut saves time is during a battery-impedance
check. The unloaded battery voltage can first be mea-
sured, if time allows, using one of the techniques
described in the previous paragraph. Then the magni-
tude of the loaded voltage drop can be quickly checked
with a single comparison to see if it is within the desired
limit.
The A/D circuitry can be invoked in both Run and Coast
Mode.
Open-Drain Drivers
Two open-drain drivers (DR1 and DR2) are activated
via the serial interface. DR1 and DR2 are grounded
1.8Ω (typical) NFETs that can sink up to 120mA. The
maximum sink current is limited by on-resistance and
package dissipation to about 240mA total sink current
for both switches. Note that DR1 and DR2 are designed
to sink current only from the main battery (BATT) and
cannot be pulled above BATT.
DR2 is controlled by an external input (DR2IN) as well
as a serial input bit. DR2IN is ANDed with the DR2ON
serial-control bit, allowing DR2 to drive an audio beep-
er. The audio-frequency clock is applied to DR2IN, and
ON/OFF gating is applied to DR2ON. Both DR2IN (pin
18) and DR2ON (serial bit) must be high for DR2 to
switch on. DR1 is controlled only by DR1ON (serial bit).
Run and Coast Modes
The MAX847’s default mode is Coast. Run Mode is
selected by either serial command (Table 2) or by
pulling the RUN pin high. The RUN serial bit and the
RUN pin are logically ORed. Both must be low to imple-
ment Coast Mode. In Coast Mode, the DC-DC convert-
er pulses only as needed to satisfy the load, holding
MAX847 operating current to typically 13µA. In Run
Mode the DC-DC converter employs fixed-frequency
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet MAX847.PDF ] | |
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