MAXIM MAX849ESE

19-1095; Rev 2; 12/97
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
Features
♦ Up to 95% Efficiency
(see Typical Output Selector Guide below)
♦ 3.3V Dual Mode™ or 2.7V to 5.5V Adj. Output
♦ 0.7V to 5.5V Input Range
♦ 0.15mW Standby Mode
♦ 300kHz PWM Mode or Synchronizable
♦ Two-Channel ADC with Serial Output
♦ Power-Good Function
Applications
Digital Cordless Phones
PCS Phones
Cellular Phones
Hand-Held Instruments
Palmtop Computers
Personal Communicators
Local 3.3V to 5V Supplies
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX848ESE
-40°C to +85°C
16 Narrow SO
MAX849ESE
-40°C to +85°C
16 Narrow SO
The devices differ only in the current limit of the
N-channel MOSFET power switch: 0.8A for the
MAX848, and 1.4A for the MAX849.
Typical Output Selector Guide
VIN
(V)
0.9
1.2
2.4
2.7
3.6
VOUT
(V)
3.3
5
3.3
5
3.3
5
3.3
5
5
MAX849 IOUT
(mA)
100
70
300
200
750
500
800
600
1000
MAX848 IOUT
(mA)
70
40
110
70
200
130
250
150
300
Typical Operating Circuit
INPUT
0.8V TO 5.5V
A/D CHANNEL 1 IN
A/D CHANNEL 2 IN
A/D CHANNEL SELECT
A/D OUTPUT
ON/OFF CONTROL
SYNC INPUT
MAX848
MAX849
AIN1
AIN2
AINSEL
DATA
ON1
ON2
CLK/SEL
POKIN
REF
LX
OUTPUT
OUT
POUT
POK
VOLTAGE MONITOR
OUTPUT
FB
GND
PGND
Pin Configuration appears at end of data sheet.
Dual Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ 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 408-737-7600 ext. 3468.
MAX848/MAX849
General Description
The MAX848/MAX849 boost converters set a new standard of high efficiency and high integration for noisesensitive power-supply applications, such as portable
phones and small systems with RF data links. The heart
of the these devices is a synchronous boost-topology
regulator that generates a fixed 3.3V output (or 2.7V to
5.5V adjustable output) from one to three NiCd/NiMH
cells or one Li-Ion cell.
Synchronous rectification provides a 5% efficiency
improvement over similar nonsynchronous boost regulators. In standby mode, pulse-skipping PFM operation
keeps the output voltage alive with only 150µW quiescent power consumption. Fixed-frequency PWM operation ensures that the switching noise spectrum is limited
to the 300kHz fundamental and its harmonics, allowing
easy post-filtering noise reduction. For even tighter
noise spectrum control, synchronize to a 200kHz to
400kHz external clock.
Battery monitoring is provided by a two-channel, voltage-to-frequency analog-to-digital converter (ADC).
One channel is intended for a single-cell battery input
(0.625V to 1.875V range), while the other channel is for
monitoring higher voltages (0V to 2.5V range).
Two control inputs are provided for push-on, push-off
control via a momentary pushbutton switch. Upon
power-up, an internal comparator monitors the output
voltage to generate a power-good output (POK).
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
ON1, ON2, OUT, POUT to GND..................................-0.3V, +6V
PGND to GND ..........................................................-0.3V, +0.3V
LX to PGND ...............................................-0.3V, (VPOUT + 0.3V)
CLK/SEL, DATA, POKIN, REF,
AINSEL, AIN1, AIN2, FB, POK to GND .....-0.3V, (VOUT + 0.3V)
Continuous Power Dissipation (TA = +70°C)
Narrow SO (derate 8.7mW/°C above +70°C) ................696mW
Operating Temperature Range
MAX848ESE/MAX849ESE .................................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature.........................................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = 0°C to +85°C,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage (Note 1)
TYP
0.7
REFERENCE
Reference Output Voltage
IREF = 0mA
REF Load Regulation
-1µA < IREF < 50µA
REF Supply Rejection
2.5V < VOUT < 5V
DC-DC CONVERTER
Output Voltage (Note 2)
VFB < 0.1V, CLK/SEL = OUT
1.23
VOUT = 3.3V
VIN = 1.2V
VOUT = 5V
VOUT = 3.3V
VIN = 2.4V
Output Current
VOUT = 5V
VOUT = 3.3V
VIN = 2.7V
VOUT = 5V
VOUT = 5V
3.17
V
5
15
mV
0.2
5
mV
3.34
3.40
V
MAX848
110
MAX849
300
MAX848
70
MAX849
200
MAX848
200
MAX849
750
MAX848
130
MAX849
500
MAX848
250
MAX849
600
MAX848
150
MAX849
800
300
1000
FB Input Current
VFB = 1.25V
Output Voltage Adjust Range
1.215
V
1.27
MAX849, VIN = 3.6V
Adjustable output, CLK/SEL = OUT
UNITS
1.25
MAX848, VIN = 3.3V
FB Regulation Voltage
1.240
mA
mA
1.265
V
200
nA
2.7
5.5
V
2.1
2.4
V
Output Voltage Lockout Range
(Note 3)
Load Regulation (Note 4)
CLK/SEL = OUT
-1.6
Minimum Start-Up Voltage (Note 5)
ILOAD < 1mA, TA > +25°C
0.9
Frequency in Start-Up Mode
VOUT = 1.5V
Operating Current in Shutdown
Current into OUT pin, V ON2 = 3.6V
2
MAX
40
4
_______________________________________________________________________________________
%
1.1
V
300
kHz
20
µA
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX848/MAX849
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = 0°C to +85°C,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
µA
Operating Current in Low-Power
Mode (Note 6)
Current into OUT pin, CLK/SEL = GND
35
90
Operating Current in Low-Noise
Mode (Note 6)
Current into OUT pin, CLK/SEL = OUT,
does not include switching losses
150
300
POUT Leakage Current
VLX = 0V, V ON2 = VOUT = 5.5V
0.1
20
µA
LX Leakage Current
VLX = V ON2 = VOUT = 5.5V
0.1
20
µA
CLK/SEL = GND
0.3
0.6
CLK/SEL = OUT
0.13
0.25
CLK/SEL = OUT
0.25
0.5
µA
DC-DC SWITCHES
Switch On-Resistance
N-channel
P-channel
CLK/SEL = OUT
N-Channel Current Limit
VCLK/SEL = 0V (Note 7)
MAX848
600
800
1000
MAX849
1100
1350
1600
MAX848
120
200
300
MAX849
250
400
550
Ω
mA
ADC
Data Output Voltage Low
ISINK = 1mA
Data Output Voltage High
ISOURCE = 1mA
VOUT - 0.4
0.4
AIN1 Input Voltage Range
AINSEL = GND
0.625
AIN2 Input Voltage Range
AINSEL = OUT
0
AIN1, AIN2 Input Current
fCLK = 400kHz, VAIN1 = VAIN2 = 2.5V
Accuracy
fCLK = 400kHz, 5ms conversion,
monotonic to 8 bits
V
V
1.875
1
V
2.5
V
2
µA
±4
% FSR
POWER-GOOD
Internal Trip Level
Rising VOUT, VPOKIN < 0.1V
2.95
3.10
V
External Trip Level
Rising VPOKIN
1.225
1.275
V
POK Low Voltage
ISINK = 1mA, VOUT = 3.6V or
ISINK = 20µA, VOUT = 1V
0.4
V
POK High Leakage Current
VOUT = VPOK = 5.5V
1
µA
POKIN Leakage Current
VPOKIN = 1.5V
50
nA
0.01
LOGIC AND CONTROL INPUTS
Input Low Voltage
Input High Voltage
1.2V < VOUT < 5.5V, ON1 and ON2 (Note 8)
0.2VOUT
VOUT = 2.7V, AINSEL and CLK/SEL
0.2VOUT
1.2V < VOUT < 5.5V, ON1 and ON2 (Note 8)
0.8VOUT
VOUT = 5.5V, AINSEL and CLK/SEL
0.8VOUT
Logic Input Current
ON1, ON2, AINSEL and CLK/SEL
Internal Oscillator Frequency
CLK/SEL = OUT
V
260
300
Oscillator Maximum Duty Cycle
80
85
External Clock Frequency Range
200
CLK/SEL Pulse Width
Not tested
CLK/SEL Rise/Fall Time
Not tested
V
1
µA
340
kHz
90
%
400
kHz
200
ns
100
ns
_______________________________________________________________________________________
3
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
ELECTRICAL CHARACTERISTICS
(VOUT = 3.6V, GND = PGND = CLK/SEL = ON1 = ON2 = AINSEL = AIN1 = AIN2 = FB = POKIN, POUT = OUT, TA = -40°C to +85°C,
unless otherwise noted.) (Note 9)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
REFERENCE
Reference Output Voltage
IREF = 0mA
1.225
1.275
V
Output Voltage (Note 3)
VFB < 0.1V, CLK/SEL = OUT,
includes load-regulation error
3.13
3.47
V
FB Regulation Voltage
Adjustable output, CLK/SEL = OUT
1.21
1.27
V
Output Voltage Lockout Range
(Note 3)
2.05
2.45
V
OUT Supply Current in Shutdown
V ON2 = 3.6V
20
µA
OUT Supply Current in Low-Power
Mode (Note 6)
CLK/SEL = GND
90
µA
OUT Supply Current in Low-Noise
Mode (Note 6)
CLK/SEL = OUT, does not include
switching losses
300
µA
DC-DC CONVERTER
DC-DC SWITCHES
Switch On-Resistance
N-channel
P-channel
CLK/SEL = OUT
N-Channel Current Limit
CLK/SEL = GND (Note 7)
CLK/SEL = GND
0.6
CLK/SEL = OUT
0.25
CLK/SEL = OUT
0.5
MAX848
600
1100
MAX849
1100
1800
MAX848
120
300
MAX849
250
550
Ω
mA
ADC
Accuracy
fCLK = 400kHz, 5ms conversion
±4
% FSR
POWER-GOOD
Internal Trip Level
Rising VOUT, VPOKIN < 0.1V
2.95
3.10
V
External Trip Level
Rising VPOKIN
1.225
1.275
V
260
340
kHz
80
90
%
LOGIC CONTROL INPUTS
Internal Oscillator Frequency
Oscillator Maximum Duty Cycle
CLK/SEL = OUT
Note 1: Minimum operating voltage. Because the MAX848/MAX849 are bootstrapped to the output, it will operate down to a 0.7V input.
Note 2: In low-power mode (CLK/SEL = GND), the output voltage regulates 1% higher than in low-noise mode (CLK/SEL = OUT or
synchronized).
Note 3: The part is in start-up mode until it reaches this voltage level. Do not apply full-load current.
Note 4: Load regulation is measured from no load to full load, where full load is determined by the N-channel switch current limit.
Note 5: Start-up is tested with Figure 2’s circuit. Output current is measured when the input and output voltages are applied.
Note 6: Supply current from the 3.34V output is measured between the 3.34V output and the OUT pin. This current correlates directly
with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. VOUT = 3.6V to keep
the internal switch open when measuring the current into the device.
Note 7: When VCLK/SEL = 0V, the inductor is forced into constant-peak-current, discontinuous operation. This is guaranteed by
testing in Figure 2’s circuit.
Note 8: ON1 and ON2 inputs have approximately 0.15VOUT hysteresis.
Note 9: Specifications to -40°C are guaranteed by design, not production tested.
4
_______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
70
VIN = 0.9V
60
90
70
PFM
PWM
1
10
100
1000
PFM
PWM
60
0.1
1
10
100
0.1
1000
10
100
1000
LOAD CURRENT (mA)
NO-LOAD BATTERY CURRENT
vs. INPUT VOLTAGE
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
START-UP VOLTAGE vs. LOAD CURRENT
(VOUT = 3.3V, PWM MODE)
TA = +25°C
6
4
TA = -40°C
12
10
TA = +85°C
8
6
TA = +25°C
1.8
4
2
3
4
5
0
6
TA = -40°C
1.2
1.0
TA = +85°C
TA = +25°C
1
2
3
5
4
0.6
6
0.01
0.1
1
10
100
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
REFERENCE VOLTAGE
vs. TEMPERATURE
REFERENCE VOLTAGE
vs. REFERENCE CURRENT
ADC LINEARITY ERROR
vs. FULL-SCALE INPUT VOLTAGE
1.249
1.248
1.246
1.244
1.242
1.238
0
20
40
60
TEMPERATURE (°C)
80
100
AIN2
-0.05
AIN1
-0.15
1.240
1.248
0.15
0.05
1000
MAX848/9 TOC-09
1.250
0.25
LINEARITY ERROR (%FS)
1.250
MAX848/9 TOC-08
1.251
1.252
REFERENCE VOLTAGE (V)
MAX848/9 TOC-07
1.252
-20
1.4
TA = -40°C
0
1
1.6
0.8
2
0
MAX848/9 TOC-06
14
2.0
MAX848/9 TOC-05
INCLUDES ALL EXTERNAL
COMPONENT LEAKAGES.
CAPACITOR LEAKAGE
DOMINATES AT
TA = +85°C
START-UP VOLTAGE (V)
8
18
16
SHUTDOWN CURRENT (µA)
MAX848/9 TOC-04
TA = +85°C
10
-40
1
LOAD CURRENT (mA)
12
0
VIN = 0.9V
LOAD CURRENT (mA)
14
2
VIN = 1.2V
70
30
0.1
80
PFM
PWM
40
40
INPUT CURRENT (mA)
VIN = 1.2V
60
VIN = 2.4V
90
50
50
REFERENCE VOLTAGE (V)
VIN = 2.4V
80
EFFICIENCY (%)
VIN = 1.2V
80
VIN = 3.6V
EFFICIENCY (%)
EFFICIENCY (%)
90
100
MAX848/9 TOC-02
VIN = 2.4V
MAX848
EFFICIENCY vs. LOAD CURRENT
(VOUT = 3.3V)
100
MAX848/9 TOC-01
100
MAX849
EFFICIENCY vs. LOAD CURRENT
(VOUT = 5V)
MAX848/9 TOC-03
MAX849
EFFICIENCY vs. LOAD CURRENT
(VOUT = 3.3V)
-0.25
0
10
20
30
40
50
60
REFERENCE CURRENT (µA)
70
80
0.1875
0.4375
0.6875
0.9375
FULL-SCALE INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
MAX848/MAX849
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
HEAVY-LOAD SWITCHING WAVEFORMS
(VOUT = 3.3V)
LINE-TRANSIENT RESPONSE
MAX848/9 TOC-11
MAX848/9 TOC-10
VOUT
A
0V
A
B
0V
0A
B
C
5ms/div
1µs/div
VIN = 1.1V, IOUT = 200mA, VOUT = 3.3V
IOUT = 0mA, VOUT = 3.3V
A = LX VOLTAGE, 2V/div
B = INDUCTOR CURRENT, 0.5A/div
C = VOUT RIPPLE, 50mV/div, AC COUPLED
A = VIN, 1.1V TO 2.1V, 1V/div
B = VOUT RIPPLE, 50mV/div, AC COUPLED
POWER-ON DELAY
(PFM MODE)
LOAD-TRANSIENT RESPONSE
MAX848/9 TOC-13
MAX848/9 TOC-12
3.3V
A
A
0A
B
C
B
2ms/div
VIN = 1.1V, VOUT = 3.3V
A = LOAD CURRENT, 0mA TO 200mA, 0.2A/div
B = VOUT RIPPLE, 50mV/div, AC COUPLED
6
200mA
0mA
5ms/div
A = VON1, 2V/div
B = VOUT, 1V/div
C = INPUT CURRENT, 0.2A/div
_______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX849
DECT LOAD-TRANSIENT RESPONSE
MAX849
GSM LOAD-TRANSIENT RESPONSE
MAX848/9 TOC-15
MAX848/9 TOC-14
3.3V
5V
A
A
B
B
0A
0A
2ms/div
1ms/div
VIN = 3.6V, VOUT = 5V, COUT = 440µF
VIN = 1.2V, VOUT = 3.3V, COUT = 440µF
A = VOUT RIPPLE, 200mV/div, AC COUPLED
B = LOAD CURRENT, 100mA TO 1A, 0.5A/div,
PULSE WIDTH = 577µs
A = VOUT RIPPLE, 200mV/div, AC COUPLED
B = LOAD CURRENT, 50mA TO 400mA, 0.2A/div,
PULSE WIDTH = 416µs
MAX849 NOISE SPECTRUM
(VOUT = 3.3V, VIN = 1.2V, RLOAD = 50Ω)
NOISE (mVRMS)
MAX848/9 TOC-16
2.7
0
0.1k
1k
10k
100k
1M
FREQUENCY (Hz)
MAX849 INTERNAL OSCILLATOR
FREQUENCY vs. TEMPERATURE
VOUT = 5V
340
320
VOUT = 3.3V
300
MAX848/9 TOC-18
360
2.0
1.8
PEAK INDUCTOR CURRENT (A)
MAX848/9 TOC-17
INTERNAL OSC. FREQUENCY (kHz)
380
MAX849 PEAK INDUCTOR CURRENT
vs. OUTPUT VOLTAGE
1.7
1.6
1.5
1.4
1.3
1.2
280
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
OUTPUT VOLTAGE (V)
_______________________________________________________________________________________
7
MAX848/MAX849
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX848/MAX849
Pin Description
8
PIN
NAME
FUNCTION
1
AIN1
ADC’s Channel 1 Input. Analog input voltage range is 0.625V to 1.875V.
2
AIN2
ADC’s Channel 2 Input. Analog input voltage range is 0V to 2.5V.
3
REF
Reference Output. Bypass with a 0.22µF capacitor to GND.
4
GND
Ground. Use for low-current ground paths. Connect to PGND with a short trace.
5
OUT
Output Sense Input. The IC is powered from OUT. Bypass to GND with a 0.1µF ceramic capacitor. Connect
OUT to POUT through a 10Ω series resistor.
6
POKIN
Power-Good Comparator Input. Connect to GND for fixed threshold (VOUT x 0.9). To adjust the threshold,
connect to a resistor divider from OUT to GND.
7
FB
Dual Mode DC-DC Converter Feedback Input. Connect to GND for fixed 3.3V output voltage. Connect to
a resistor divider from OUT to GND to adjust the output voltage. Minimize noise coupling from switching
signals to FB.
8
POK
Power-Good Output. This open-drain output is pulled low when the output voltage (VOUT) drops below
the internally set threshold (fixed threshold), or when the voltage at POKIN drops below VREF (adjustable
threshold).
9
AINSEL
10
DATA
ADC’s Input Channel Selector. Pull low to select AIN1 and drive high to select AIN2.
ADC’s Serial Output. Pulsed output, RZ format. Full scale is fOSC/2 (fCLK/2 in external sync mode). The
DATA output is low when VCLK/SEL = 0V (PFM mode).
External Clock Input/Regulator’s Switching Mode Selector.
CLK/SEL = low: low-power, low-quiescent PFM mode. Delivers 100mW of output power.
CLK/SEL = high: low-noise, high-power PWM mode, switching at a constant frequency (300kHz).
CLK/SEL = driven with external clock: low-noise, high-power, synchronized PWM mode. The internal
oscillator is synchronized to the external clock (200kHz ~ 400kHz). Turning the DC-DC converter on with
VCLK/SEL = 0V also serves as a soft-start function, since the peak inductor current is limited to 30% of the
nominal value.
11
CLK/SEL
12
PGND
13
LX
14
POUT
15
ON2
OFF Control Input. When ON1 = 0 and ON2 = 1, the IC is off.
16
ON1
ON Control Input. When ON1 = 1 or ON2 = 0, the IC is on.
Source of the Internal N-Channel Power MOSFET. Connect to high-current ground path.
Drain of the Internal N-Channel Power MOSFET and P-Channel Synchronous Rectifier
Source of the Internal P-Channel Synchronous Rectifier MOSFET. Connect an external Schottky diode from
LX to POUT. Bypass to PGND with a 0.1µF ceramic capacitor as close to the IC as possible.
_______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX848/MAX849
OUT
MAX848/MAX849
START-UP
OSCILLATOR
2.25V
EN
POUT
Q
Q
D
PCH
0.25Ω
ON1
ON
ON2
REF
1.25V
RDY
REF
EN
CLK/SEL
FB
FEEDBACK
AND
POWER-GOOD
SELECT
POKIN
Q
OSC
300kHz
OSCILLATOR
GND
LX
EN
PFM/PWM
FEEDBACK
NCH
0.13Ω
PGND
MODE
PFM/PWM
CONTROLLER
POK
N
EN
AINSEL
AIN1
ADC
DATA
AIN2
Figure 1. Functional Diagram
_______________Detailed Description
The MAX848/MAX849 combine a switching regulator,
N-channel power MOSFET, P-channel synchronous
rectifier, precision reference voltage, power-good indicator, and battery voltage monitor, all in a single monolithic device. The MAX848/MAX849 are powered
directly from the output. The output voltage is factory
preset to 3.3V or adjustable from 2.7V to 5V with external resistors (Dual Mode™ operation). These devices
start from a low 1V input voltage and remain operational down to 0.7V. The MAX848/MAX849 operate with
either one to three NiCd/NiMH cells or one Li-Ion cell.
At power-up, an internal low-voltage oscillator drives
the N-channel power switch, and the output voltage
slowly builds up. The oscillator has a 25% nominal duty
cycle to prevent current build-up in the inductor. An
output voltage in excess of the nominal 2.25V lockout
voltage activates the error comparator and internal timing circuitry. The device resumes operation in either
pulse-frequency-modulation (PFM) low-power mode or
pulse-width-modulation (PWM) low-noise mode, selected by the logic control, CLK/SEL. Figure 2 shows the
standard application circuit for the MAX849 configured
in the high-power PWM mode.
On/Off Control
The MAX848/MAX849 are turned on or off by logic
input pins ON1 and ON2 (Table 1). When ON1 = 1 or
ON2 = 0, the part is on. When ON1 = 0 and ON2 = 1,
the part is off. Both inputs have logic trip points near
0.5 x VOUT with 0.15 x VOUT hysteresis.
Table 1. On/Off Logic Control
ON1
0
ON2
0
0
1
Off
1
0
On
1
1
On
MAX848/MAX849
On
Operating Modes
The MAX848/MAX849 operate in either PFM, PWM, or
PWM synchronized to an externally applied clock signal. Table 2 lists each operating mode.
_______________________________________________________________________________________
9
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
VIN = 1.1V
OUT
C2
0.1µF
D
LOGIC HIGH
POUT
10Ω
R3
100k
Q
*
POUT
3.3V @
200mA
D1
MBR0520L
MAX849
GND
POK
ON1
C5
0.1µF
R
C4
2 x 100µF
L1
10µH
C1
22µF
LX
CLK/SEL PGND
C3
FB
0.22µF
POKIN
REF
ON2
LX
FEEDBACK
S
N
Q
REF
R
PFM-MODE
CURRENTLIMIT LEVEL
CURRENT
SENSE
PGND
* HEAVY LINES INDICATE
HIGH-CURRENT PATH.
Figure 2. 3.3V Preset Output
Figure 3. Controller Block Diagram in PFM Mode
Table 2. Selecting Operating Mode
CLK/SEL
MODE
0
PFM
1
PWM
External clock
(200kHz ~ 400kHz)
Synchronized PWM
Low-Power PFM Mode
When CLK/SEL is pulled low, the MAX848/MAX849 operate in low-power, low-supply-current PFM mode. Pulsefrequency modulation provides the highest efficiency at
light loads. The P-channel rectifier is turned off to reduce
gate-charge losses, and the regulator operates in discontinuous mode. The N-channel power MOSFET is kept
on until the inductor current ramps to 30% of the current
limit. The inductor energy is delivered to the output
capacitor when the switch turns off. A new cycle is inhibited until the inductor current crosses zero. Zero current
detection is accomplished by sensing the LX voltage
crossing the output voltage. Figure 3 shows the block
diagram for the PFM controller.
Low-Noise PWM Mode
When CLK/SEL is pulled high, the MAX848/MAX849
operate in high-power, low-noise, current-mode PWM,
switching at the 300kHz nominal internal oscillator frequency. The internal rectifier is active in this mode,
and the regulator operates in continuous mode. The
N-channel power MOSFET turns on until either the output
voltage is in regulation or the inductor current limit is
reached (0.8A for the MAX848 and 1.4A for the
MAX849). The switch turns off for the remainder of the
cycle and the inductor energy is delivered to the output
10
capacitor. A new cycle is initiated on the next oscillator
cycle. In low-noise applications, the fundamental and the
harmonics generated by the fixed switching frequency
can easily be filtered. Figure 4 shows the block diagram
for the PWM controller.
The MAX848/MAX849 enter synchronized current-mode
PWM when a clock signal (200kHz < fCLK < 400kHz) is
applied to CLK/SEL. The internal synchronous rectifier
is active and the switching frequency is synchronized
to the externally applied clock signal. For wireless
applications, this ensures that the harmonics of the
switching frequencies are predictable and can be kept
outside the IF band(s). High-frequency operation permits low-magnitude output ripple voltage.
The MAX848/MAX849 are capable of providing a stable
output even with a rapidly pulsing load (GSM, DECT),
such as from a transmitter power amplifier in digital cordless phones (see Typical Operating Characteristics).
In PWM mode, the use of the synchronous rectifier
ensures constant-frequency operation, regardless of
the load current.
Setting the Output Voltage Externally
The MAX848/MAX849 feature Dual Mode operation.
The output voltage is preset to 3.3V (FB = 0V), or it can
be adjusted from 2.7V to 5.5V with external resistors
R1, R2, and R3, as shown in Figure 5. To set the output
voltage externally, select resistor R3 in the 10kΩ to
100kΩ range. The values for R1 and R2 are given by:
R2 = R3(VOUT / VTRIP - 1)
R1 = (R3 + R2)(VTRIP / VREF - 1)
______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX848/MAX849
POUT
P
OUT
FEEDBACK
MAX848
MAX849
REF
LX
R Q
OUTPUT
R1
POKIN
N
R2
S
FB
GND
PGND
POK
R3
PWM-MODE
CURRENTLIMIT LEVEL
OSC
Figure 4. Controller Block Diagram in PWM Mode
where VREF = 1.25V, VOUT is the desired output voltage, and VTRIP is the desired trip level for the powergood comparator.
Power-OK
The MAX848/MAX849 feature a power-good comparator. This comparator’s open-drain output, POK, is
pulled low when the output voltage falls below the nominal internal threshold level of 3V with POKIN = 0V. To
set the power-good trip level externally, refer to the
Setting the Output Voltage Externally section.
Figure 5. Adjustable Output Voltage and Power-Good Trip Level
AIN1
AINSEL
C
C
AIN2
Q
2 x REF
REF
Analog-to-Digital Converter (ADC)
The MAX848/MAX849 have an internal, two-channel, serial ADC. The ADC converts an analog input voltage into a
digital stream available at the DATA pin. The converter
skips clock pulses in proportion to the input voltage.
Output format is a return-to-zero bit stream with a bit
duration of 1/fCLK. At zero-scale input voltage, all pulses
are skipped and DATA remains low; with a positive fullscale input voltage, no pulses are skipped; and at midscale, every other pulse is skipped. The ADC’s clock is
one-half of the externally applied clock signal or one-half
of the internal 300kHz clock available at LX. In PFM
mode, the converter is not active and DATA is driven low.
Channel 1, AIN1, has an input voltage range of 0.625V
to 1.875V and is selected when AINSEL is low. Channel
2, AIN2, accepts inputs in the 0V to 2.5V range and is
selected when AINSEL is pulled high (Figure 6).
The ADC is a switched-capacitor type; therefore, an
anti-aliasing filter might be required at the inputs. Insert
a 1kΩ series resistor and a 0.01µF filter capacitor in
noisy environments.
D
C/2
C/2
OSC
÷2
DATA
Figure 6. A/D Converter Block Diagram
Timer Function Implementation
Implement the necessary counter functions either with
discrete hardware or with microcontroller (µC) implementations. The output resolution depends on how
many of the ADC clock pulses are counted, as shown
in Figure 7.
Hardware Implementation
A complete hardware solution can be implemented
using either two counters or an ASIC. Resolution
depends on how many pulses are counted. The main
advantage of the discrete hardware implementation is
that accuracy is not affected by interrupt latency associated with the µC solution.
______________________________________________________________________________________
11
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
COUNTING FOUR PULSES
fOSC/2
DATA
GIVES YOU 2-BIT RESOLUTION
Figure 7. Bit Stream at 1/2 Full Scale
When using two counters of the same length, as shown
in Figure 8, one counter (A) just counts the A/D clock
pulses (fOSC/2), and the other counter (B) counts DATA
output pulses. When counter A overflows (for example,
after 256 clock cycles for an 8-bit counter), counter B is
disabled. The controller reads the counter B output
data and calculates the analog voltage present at the
ADC’s input.
All µC Implementation
This implementation uses a µC timer and a counter.
The timer and the counter are reset at the same time.
The counter counts data-output pulses applied at its
input. When the timer times out, an interrupt is asserted. The µC then reads the state of the counter register.
The interrupt-handling overhead can cause the counter
to count more pulses than desired. Accuracy depends
on how long the µC needs to read the counter. No
errors will occur if the counter is disabled within one
clock period. Interrupt latency reduces accuracy. The
main advantage of this implementation is that no external hardware is required.
__________________Design Procedure
Inductor Selection
The MAX848/MAX849’s high switching frequency allows
the use of a small inductor. Use a 10µH inductor for the
MAX849 and a 22µH inductor for the MAX848. Inductors
with a ferrite core or equivalent are recommended; powder iron cores are not recommended for use with high
switching frequencies. Make sure the inductor’s saturation rating (the current at which the core begins to saturate and inductance starts to fall) exceeds the internal
current limit: 0.8A for the MAX848 and 1.4A for the
MAX849. However, it is generally acceptable to bias the
inductor into saturation by approximately 20% (the point
where the inductance is 20% below the nominal value).
For highest efficiency, use a coil with low DC resistance,
preferably under 100mΩ. To minimize radiated noise,
use a toroid, pot core, or shielded inductor. See Table 5
for a list of suggested inductor suppliers.
12
VCC
CLOCK/SEL
OR LX
A
÷2
EN
CLK
CLR
CLEAR
DATA OUTPUT
CARRY OUTPUT
8-BIT COUNTER
RC
B
CLR
CLK
8-BIT COUNTER
EN
LATCH
Figure 8. Discrete Hardware Solution for Counting A/D Output
Data Pulses
Diode Selection
The MAX848/MAX849’s high switching frequency
demands a high-speed rectifier. Schottky diodes, such
as the 1N5817 or MBR0520L, are recommended. Make
sure the diode’s current rating exceeds the maximum
load current and that its breakdown voltage exceeds
VOUT.
The Schottky rectifier diode carries load currents only in
the PFM operating mode, since the P-channel synchronous rectifier is disabled. Therefore, the current rating
need not be high (0.5A is sufficient). In PFM mode, the
voltage drop across the rectifier diode causes efficiency loss. However, when operating in PWM mode, the
internal P-channel synchronous rectifier is active and
efficiency loss due to the rectifier diode is minimized.
For high-temperature applications, Schottky diodes
may be inadequate due to their high leakage currents;
use high-speed silicon diodes such as the MUR105 or
EC11FS1. At heavy loads and high temperatures, the
benefits of a Schottky diode’s low forward voltage may
outweigh the disadvantage of high leakage current.
See Table 4 for a list of suggested diode suppliers.
______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
µC
MAX848
MAX849
ON2
OUT
VDD
I/O
MAX848
MAX849
I/O
ON1
MAX8865/MAX8866 DUALS
MAX8863/MAX8864 SINGLES
PA
µC
1MΩ
Figure 9. Momentary Pushbutton On/Off Switch
RADIO
Figure 10. Typical Phone Application
Applications Information
Capacitor Selection
Input Bypass Capacitors
A 22µF, low-ESR input capacitor will reduce peak currents and reflected noise due to inductor current ripple.
Smaller ceramic capacitors may also be used for light
loads or in applications that can tolerate higher input
ripple.
Output Filter Capacitors
Two 100µF (single 100µF for the MAX848), 10V, lowESR, output filter capacitors typically exhibit 30mV ripple when stepping up from 1.2V to 3.3V at 200mA
(100mA for the MAX848). Bypass the MAX848/MAX849
supply input, OUT, with a 0.1µF ceramic capacitor
to GND. Also bypass POUT to PGND with a 0.1µF
ceramic capacitor.
The filter capacitors’ equivalent series resistance (ESR)
affects efficiency and output ripple. The output voltage
ripple is the product of the peak inductor current and
the output capacitor’s ESR. Low-ESR, surface-mount
tantalum capacitors are currently available from
Sprague (595D series) and AVX (TPS series). Sanyo
OS-CON organic-semiconductor, through-hole capacitors also exhibit very low ESR, and are especially useful
for operation at cold temperatures. See Table 5 for a list
of suggested capacitor suppliers.
Using a Momentary On/Off Switch
A momentary pushbutton switch can be used to turn
the MAX848/MAX849 on and off.
As shown in Figure 9, ON1 is pulled low and ON2 is
pulled high when the part is off. When the momentary
switch is pressed, ON2 is pulled low and the regulator
turns on. The switch should be on long enough for the
µC to exit reset. The controller issues a logic high to
ON1, which guarantees that the part will stay on,
regardless of the switch state.
To turn off the regulator, the switch is pressed and held.
The controller reads the switch status and pulls ON1
low. The switch is released and ON2 is pulled high.
Power Amplifier (PA) and Radio Supply
in a Typical Phone Application
The MAX849 is an ideal power supply for the power
amplifier (PA) and the radio used in digital cordless
and PCS phones (Figure 10). The PA is directly powered by the MAX849 for maximum output swing. Postlinear regulators power the controller and the radio. In
addition, they reduce switching noise and ripple. Table
3 lists the output power available when operating with
one or more NiCd/NiMH cells or one Li-Ion cell.
Table 3. Available Output Power
INPUT VOLTAGE
(V)
OUTPUT VOLTAGE:
PA POWER SUPPLY
(V)
OUTPUT POWER
(W)
1 NiCd/NiMH
1.2
3.3
0.9
2 NiCd/NiMH
2.4
3.3
2.4
2 NiCd/NiMH
2.4
5.0
2.6
3 NiCd/NiMH or 1 Li-Ion
3.6
5.0
4.3
NUMBER OF CELLS
______________________________________________________________________________________
13
MAX848/MAX849
1MΩ
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
the timing resistor should not exceed the difference
between the output voltage and the µC reset threshold
voltage. This resistor should be large enough to minimize the shutdown current.
µC
MAX848
MAX849
OUT
VCC
µC-Controlled Shutdown
The MAX848/MAX849 turn on when ON1 = 1 or ON2 = 0.
The µC monitors the battery voltage and turns off the
device (forces ON1 low and ON2 high) when the battery is weak.
R
RESET
POK
C
Layout Considerations
Figure 11. Power-On Reset Delay
Power-On Reset Delay
Adding a timing capacitor from POK to GND generates
a power-on reset delay. The reset time constant is
determined by the pull-up resistor and timing capacitor
(Figure 11). When power is turned on, POK is low and
the capacitor is shorted. When the output voltage
reaches regulation, POK goes high and the capacitor
slowly charges to the output voltage.
The timing resistor value depends on the controller’s
RESET input leakage current. The voltage drop across
Due to high inductor current levels and fast switching
waveforms, which radiate noise, proper PC board layout is essential. Protect sensitive analog grounds by
using a star ground configuration. Minimize ground
noise by connecting PGND, the input bypass capacitor
ground lead, and the output filter capacitor ground lead
to a single point (star ground configuration). Also, minimize lead lengths to reduce stray capacitance and
trace resistance.
If an external resistor divider is used to set the output
voltage (Figure 5), the trace from FB to the resistors
must be extremely short and must be shielded from
switching signals, such as CLK, DATA, or LX.
Table 4. Component Selection Guide
PRODUCTION
INDUCTORS
CAPACITORS
Surface Mount
Sumida CDR63B, CD73, CDR73B, CD74B series
Coilcraft DO1608, DO3308, DT3316 series
Matsuo 267 series
Sprague 595D series
AVX TPS series
Through Hole
Sumida RCH654 series
Sanyo OS-CON series
Nichicon PL series
Table 5. Component Suppliers
SUPPLIER
PHONE
Motorola MBR0520L
Motorola 1N5817
Chip Information
FAX
AVX
USA: 803-946-0690
800-282-4975
803-626-3123
Coilcraft
USA: 847-639-6400
847-639-1469
Matsuo
USA: 714-969-2491
714-960-6492
Motorola
USA: 602-303-5454
602-994-6430
Sanyo
USA: 619-661-6835
Japan: 81-7-2070-6306
619-661-1055
81-7-2070-1174
Sumida
USA: 847-956-0666
Japan: 81-3-3607-5111
847-956-0702
81-3-3607-5144
14
DIODES
TRANSISTOR COUNT: 2059
______________________________________________________________________________________
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
MAX848/MAX849
Pin Configuration
TOP VIEW
AIN1 1
16 ON1
AIN2 2
15 ON2
REF 3
14 POUT
GND 4
OUT 5
MAX848
MAX849
13 LX
12 PGND
11 CLK/SEL
POKIN 6
10 DATA
FB 7
9
POK 8
AINSEL
Narrow SO
SOICN.EPS
Package Information
______________________________________________________________________________________
15
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
NOTES
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.