MAX1642C/D-T [MAXIM]
Switching Regulator, 1A;
| 型号： | MAX1642C/D-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switching Regulator, 1A 开关 |
| 文件： | 总12页 (文件大小：130K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1183; Rev 0; 6/97
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
♦ Built-In Synchronous Rectifier
The MAX1642/MAX1643 are high-efficiency, low-voltage,
step-up DC-DC converters intended for devices pow-
ered by a single alkaline cell. They feature low quies-
cent supply currents and are supplied in the ultra-small
µMAX package, which is only 1.1mm high. The guaran-
teed start-up voltage is 0.88V.
♦ 0.88V Guaranteed Start-Up
♦ Ultra-Small µMAX Package: 1.1mm High
♦ 83% Efficiency
Ea c h d e vic e c ons is ts of a n inte rna l 1Ω, N-c ha nne l
MOSFET power switch; a built-in synchronous rectifier
that acts as the catch diode; an oscillator; a reference;
and pulse-frequency-modulation (PFM) control circuitry.
Both devices feature an independent undervoltage
comparator (PFI/PFO). The MAX1642 also includes a
2µA logic-controlled shutdown mode. The MAX1643
offers a dedicated low-battery detector (BATTLO) in
lieu of shutdown.
♦ 4µA Quiescent Supply Current into BATT Pin
♦ 2µA Logic-Controlled Shutdown (MAX1642)
♦ Two Undervoltage Detectors (MAX1643)
♦ 2V to 5.2V Output Range
♦ 20mA Output Current at 1.2V Input
♦ Reverse Battery Protection
The output voltage for each device is preset to 3.3V
±4%, or can be adjusted from +2V to +5.2V using only
two resistors.
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
MAX1642C/D
MAX1642EUA
MAX1643C/D
MAX1643EUA
8 µMAX
Dice*
________________________Ap p lic a t io n s
8 µMAX
Pagers
*Dice are tested at T = +25°C.
A
Remote Controls
Note: To order these devices shipped in tape and reel, add a -T
to the part number.
Pointing Devices
Personal Medical Monitors
Single-Cell Battery-Powered Devices
_________________P in Co n fig u ra t io n s
TOP VIEW
1
2
3
4
8
7
6
5
OUT
LX
BATT
PFI
__________Typ ic a l Op e ra t in g Circ u it
MAX1642
µMAX
GND
FB
PFO
SHDN
INPUT
0.88V TO 1.65V
OUTPUT
3.3V
100µH
OUT
LX
22µF
22µF
MAX1642
BATT
1
2
3
4
8
7
6
5
OUT
LX
BATT
PFI
ON
SHDN
OFF
MAX1643
µMAX
PFI
GND
PFO
FB
LOW-BATTERY
DETECTOR INPUT
LOW-BATTERY
DETECTOR OUTPUT
GND
FB
BATTLO
PFO
________________________________________________________________ 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.
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
ABSOLUTE MAXIMUM RATINGS
BATT to GND ...........................................................-0.3V to 6.0V
BATT Forward Current ..........................................................0.5A
OUT to GND.............................................................-0.3V to 6.0V
OUT, LX Current.......................................................................1A
LX to GND................................................................-0.3V to 6.0V
SHDN, FB, BATTLO, PFO to GND...........................-0.3V to 6.0V
Continuous Power Dissipation
µMAX (derate 4.1mW/°C above 70°C)..........................330mW
Operating Temperature Range
MAX1642EUA/MAX1643EUA ............................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering, 10sec) .............................+300°C
PFI to GND ............................................................-0.3V to V
BATT
Reverse Battery Current (T = +25°C) (Note 1) ...............220mA
A
Note 1: The reverse battery current is measured from the Typical Operating Circuit’s input terminal to GND when the battery is con-
nected backward. A reverse current of 220mA will not exceed package dissipation limits but, if left for an extended time
(more than 10 minutes), may degrade performance.
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
(V
BATT
= V
= 1.3V, I
= 0mA, FB = GND, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
SHDN
LOAD
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2/MAX1643
Minimum Operating Input Voltage
Maximum Operating Input Voltage
Start-Up Voltage (Note 2)
Start-Up Voltage Tempco
Output Voltage
V
0.7
V
V
BATT(MIN)
1.65
R
= 3kΩ, T = +25°C
0.88
V
L
A
-2
mV/°C
V
V
OUT
V
FB
< 0.1V
3.16
2.0
3.30
3.44
5.2
Output Voltage Range
External feedback
External feedback
V
FB Set Voltage
V
FB
1.18
1.225
1
1.27
1.5
V
N-Channel On-Resistance
P-Channel On-Resistance
P-Channel Catch-Diode Voltage
On-Time Constant
V
OUT
= 3.3V
= 3.3V
Ω
V
OUT
1.5
0.8
25
2.2
Ω
I
= 100mA, P-channel switch off
V
DIODE
K
0.9V < V
< 1.5V (t
= K / V )
BATT
17
1
35
1.5
18
6.5
1
V-µs
BATT
ON
Off-Time Tracking Ratio (Note 3)
Quiescent Current into OUT
Quiescent Current into BATT
Shutdown Current into OUT
Shutdown Current into BATT
Efficiency
RATIO
0.9V < V
< 1.5V, V
= 3.3V
BATT
OUT
I
V
OUT
= 3.5V
11
4
µA
µA
µA
µA
%
QOUT
I
QBATT
I
V
OUT
= 3.5V (MAX1642)
= 1.0V (MAX1642)
= 20mA
0.1
2
SHDN,OUT
I
V
BATT
3.5
SHDN,BATT
η
I
80
LOAD
FB Input Current
V
= 1.3V
10
632
10
nA
mV
nA
V
FB
PFI Trip Voltage
Falling PFI, hysteresis = 1%
590
614
1.0
PFI Input Current
V
PFI
= 650mV
= 0V, V
V
V
PFI
= 3.3V, I = 1mA
SINK
0.4
1
PFO, BATTLO Low Output Voltage
PFO, BATTLO Leakage Current
BATTLO Trip Voltage
OL
OUT
V
PFI
= 650mV, V
= 6V
µA
V
PFO
V
OUT
= 3.3V, hysteresis = 2% (MAX1643)
0.96
80
1.04
20
V
IL
% of V
(MAX1642)
(MAX1642)
BATT
%
SHDN Input Low Voltage
SHDN Input High Voltage
SHDN Input Current
BATT
V
% of V
%
IH
(MAX1642)
10
nA
2
_______________________________________________________________________________________
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
ELECTRICAL CHARACTERISTICS
(V
BATT
= V
= 1.3V, I = 0mA, FB = GND, T = -40°C to +85°C, unless otherwise noted.) (Note 4)
LOAD A
SHDN
PARAMETER
SYMBOL
CONDITIONS
MIN
2.99
1.11
MAX
3.56
1.32
1.5
UNITS
V
Output Voltage
FB Set Voltage
V
OUT
V
< 0.1V
FB
V
FB
External feedback
V
N-Channel On-Resistance
P-Channel On-Resistance
On-Time Constant
V
OUT
= 3.3V
= 3.3V
Ω
V
OUT
2.2
Ω
K
0.9V < V
< 1.5V (t
= K / V )
BATT
12.4
38.2
18
V-µs
µA
µA
µA
µA
mV
BATT
ON
Quiescent Current into OUT
Quiescent Current into BATT
Shutdown Current into OUT
Shutdown Current into BATT
PFI Trip Voltage
I
V
OUT
= 3.5V
QOUT
I
6.5
QBATT
I
V
OUT
= 3.5V (MAX1642)
= 1.0V (MAX1642)
BATT
1
SHDN,OUT
I
V
3.5
SHDN,BATT
Falling PFI, hysteresis = 1%
550
662
Falling V , V = 3.3V, hysteresis = 2%
(MAX1643)
BATT
OUT
0.93
1.06
V
BATTLO Trip Voltage
Note 2: Start-up guaranteed by correlation to measurements of device parameters (i.e., switch on-resistance, on-times, off-times, and
output voltage trip points).
t
x V
BATT
- V
BATT
ON
Note 3:
. This guarantees discontinuous conduction.
x RATIO
t
=
OFF
V
OUT
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(Circuit of Figure 4, V
= 1.2V, R1 + R2 = 1MΩ, T = +25°C, unless otherwise noted.)
A
BATT
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
(V = 2.4V)
OUT
(V = 2.4V)
OUT
(V = 3.3V)
OUT
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
= 1.6V
V
= 1.6V
IN
IN
V
= 1.6V
IN
V = 1.2V
IN
V
IN
= 1.2V
V
= 1.2V
IN
V
= 1.0V
V
= 1.0V
IN
IN
V
= 1.0V
IN
V
= 0.85V
V
IN
= 0.85V
IN
V = 0.85V
IN
L1 = 100µH
L1 = 100µH
SUMIDA CD54-101
L1 = 150µH
TDK NLC565050T-151K
SUMIDA CD54-101
0.01
0.1
1
10
100
0.01
0.1
1
10
100
0.01
0.1
1
10
100
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 4, V
= 1.2V, R1 + R2 = 1MΩ, T = +25°C, unless otherwise noted.)
A
BATT
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
(V = 5.0V)
OUT
(V = 3.3V)
OUT
(V = 5.0V)
OUT
100
90
100
90
80
70
60
50
40
30
20
10
0
100
90
V = 1.6V
IN
V
IN
= 1.6V
V
= 1.6V
IN
V
= 1.0V
V
IN
= 1.0V
IN
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
V
IN
= 0.85V
V
= 0.85V
IN
V
IN
= 1.2V
V
IN
= 1.2V
V
= 1.2V
IN
V
= 1.0V
IN
V
IN
= 0.85V
L1 = 100µH
SUMIDA CD54-101
L1 = 150µH
TDK NLC565050T-151K
L1 = 150µH
TDK NLC565050T-151K
0.01
0.1
1
10
100
0.01
0.1
1
10
100
0.01
0.1
1
10
100
6
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
NO-LOAD BATTERY CURRENT
vs. TEMPERATURE
NO-LOAD BATTERY CURRENT
vs. INPUT VOLTAGE
BATT AND OUT PIN QUIESCENT CURRENTS
vs. TEMPERATURE
30
140
10,000
V
V
OUT
= 1.2V
= 3.6V
V
V
= 1.2V
= 3.3V
BATT
BATT
120
100
OUT
25
20
1000
100
80
60
40
V
OUT
= 5.0V
15
10
5
I
OUT
20
0
V
OUT
= 2.5V OR 3.3V
I
BATT
10
0
0.8
1.0
1.2
1.4
1.6
1.8
-40 -20
0
20
40
60
80 100
-40 -20
0
20
40
60
80
100
INPUT VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
MINIMUM START-UP INPUT VOLTAGE
vs. OUTPUT CURRENT
MINIMUM START-UP INPUT VOLTAGE
vs. OUTPUT CURRENT
1.6
1.5
1.6
1.5
L1 = 150µH
TDK NLC565050T-151K
L1 = 100µH
SUMIDA CD54-101
1.4
1.3
1.2
1.4
1.3
1.2
V
OUT
= 5V
V
OUT
= 5V
1.1
1.0
0.9
0.8
1.1
1.0
0.9
0.8
V
OUT
= 2.4V, 3.3V
V
OUT
= 2.4V, 3.3V
0.7
0.6
0.7
0.6
2
4
6
8
10 12 14
0
16
0
5
10
15
20
25
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
4
_______________________________________________________________________________________
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 4, V
= 1.2V, R1 + R2 = 1MΩ, T = +25°C, unless otherwise noted.)
A
BATT
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
SWITCHING WAVEFORMS
35
30
25
20
18
16
14
12
V
OUT
= 2.4V
V
OUT
= 2.4V
A
B
C
V
OUT
= 3.3V
20
15
10
8
V
OUT
= 3.3V
V
OUT
= 5V
V
OUT
= 5V
6
10
4
2
0
L1 = 100µH
SUMIDA CD54-101
L1 = 150µH
TDK NLC565050T-151K
5
0
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
INPUT VOLTAGE (V)
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
INPUT VOLTAGE (V)
10ms/div
V
OUT
= 3.3V, V = 1.2V, I = 12mA
IN OUT
A: LX, 2V/div, L1 = TDK NLC565050T-151K
B: OUT, 20mV/div, 3.3V DC OFFSET
C: INDUCTOR CURRENT, 100mA/div
SHUTDOWN RESPONSE AND
INDUCTOR CURRENT
LINE-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
A
A
B
A
B
B
C
400µs/div
10ms/div
400µs/div
V
OUT
= 3.3V, LOAD = 15mA
V
OUT
= 3.3V, V
= 1.2V, I = 5mA
V
OUT
= 3.3V, V
= 1.2V
BATT OUT
BATT
A: OUT, 50mV/div, 3.3V DC OFFSET
A: OUT, 1V/div
B: INDUCTOR CURRENT, 200mA/div
C: SHDN, 2V/div
A: OUT, 20mV/div, 3.3V DC OFFSET
B: LOAD, 2mA to 20mA, 10mA/div
B: V , 1V to 1.5V, 500mV/div
BATT
_______________________________________________________________________________________
5
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
MAX1642
MAX1643
1
2
1
2
BATT
PFI
IC Battery-Power Input. Sense input for BATTLO comparator (MAX1643 only).
Power-Fail Input. When the voltage on PFI drops below 614mV, PFO sinks current.
Open-Drain Battery-Low Output. When the voltage at BATT drops below 1V, BATTLO
sinks current.
—
3
BATTLO
3
4
4
Open-Drain Power-Fail Output. Sinks current when PFI drops below 614mV.
Active-Low Shutdown Input. Connect to BATT for normal operation.
PFO
—
SHDN
Feedback Input for adjustable-output operation. Connect FB to an external resistor voltage
divider between OUT and GND. Connect to GND for fixed-output operation.
5
5
FB
6
7
6
7
GND
LX
Ground
2/MAX1643
N-Channel MOSFET Switch Drain and P-Channel Synchronous-Rectifier Drain
Power Output. Feedback input for fixed 3.3V operation and IC power input. Connect filter
capacitor close to OUT.
8
8
OUT
Op e ra t in g P rin c ip le
_______________De t a ile d De s c rip t io n
The MAX1642/MAX1643 employ a proprietary pulse-
frequency-modulation (PFM) control scheme that com-
b ine s the ultra -low q uie s c e nt c urre nt tra d itiona l of
pulse-skipping PFM converters with the high-load effi-
ciency of pulse-width-modulation (PWM) converters.
The on-time and minimum off-times are varied as a
function of the input and output voltages:
The MAX1642/MAX1643 each consist of an internal 1Ω,
N-channel MOSFET power switch, a built-in synchro-
nous rectifier that acts as the catch diode, an oscillator,
a reference, and PFM control circuitry (Figure 1).
The s e d e vic e s a re op timize d for a p p lic a tions with
power-management features that operate from one
alkaline cell, such as pagers, remote controls, and bat-
tery-powered instruments. They are designed to meet
the specific demands of the operating states character-
istic of such systems:
K
t
t
=
ON
V
BATT
1) Primary battery is good and the load is active: In
this state, the system draws tens of milliamperes,
and the MAX1642/MAX1643 typically offer 80% effi-
ciency.
1.2 x K
- V
=
OFF(MIN)
V
OUT
BATT
whe re K is typ ic a lly 25V-µs . This e na b le s the
MAX1642/MAX1643 to maintain high efficiency over a
wide range of loads and input/output voltages. The DC-
DC converter is powered from the OUT pin.
2) Primary battery is good and the load is sleeping: In
this state, the load is drawing hundreds of microam-
peres, and the DC-DC converter IC draws very low
quiescent current. In many applications, the load is
expected to be in this state most of the time.
6
_______________________________________________________________________________________
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
Whe n the e rror c omp a ra tor de te c ts tha t the output
the P-channel synchronous rectifier remains off and
either its body diode or an external diode is used as an
output rectifier. Reduce the load as needed to allow
s ta rt-up with inp ut volta g e s b e low 2V (s e e Typ ic a l
Operating Characteristics).
voltage is too low, it turns on the internal N-channel
MOSFET switch until the on-time is satisfied (see Figure
1 and the Standard Application Circuits, Figures 2 and
3). During the on-time, current ramps up in the induc-
tor, storing energy in a magnetic field. When the MOS-
FET turns off, during the second half of each cycle, the
magnetic field collapses, causing the inductor voltage
to forc e c urre nt throug h the s ync hronous re c tifie r,
transferring the stored energy to the output filter capac-
itor and load. The output filter capacitor stores charge
while current from the inductor is high, then holds up
the output voltage until the second half of the next
switching cycle, smoothing power flow to the load.
S h u t d o w n (MAX1 6 4 2 )
Pulling SHDN low places the MAX1642 in shutdown
mode (I
= 2µA typical). In shutdown, the internal
SHDN
s witc hing MOSFET turns off, PFO g oe s hig h-
impedance, and the synchronous rectifier turns off to
prevent reverse current from flowing from the output
back to the input. However, there is still a forward cur-
rent path through the synchronous-rectifier body diode
from the input to the output. Thus, in shutdown, the out-
put remains one diode drop below the battery voltage
Bo o t s t ra p DC-DC Blo c k
The bootstrap block contains a low-voltage start-up
oscillator. This oscillator pumps up the output voltage
to approximately 1.7V, where the main DC-DC con-
verter can operate. The oscillator is powered from the
BATT input and drives an NPN switch. During start-up,
(V ). To disa b le the shutdown fe a ture , c onne c t
BATT
SHDN (a logic input) to BATT.
BATT
OUT
TIMING
TON
TOFF
0.5REF
PDRV
NDRV
P
EN
LOGIC
PFI
MAX1642
LX
FB
PFO
N
REF
START-UP
OSCILLATOR
RFRDY
REF
REF
0.5REF
GND
OUT
1.7V
SHDN
Figure 1. MAX1642 Functional Diagram
_______________________________________________________________________________________
7
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
BATTLO (MAX1 6 4 3 )
The MAX1643 contains an on-chip comparator for low-
100µH, 350mA
0.88V to 1.65V INPUT
battery detection. If the voltage at BATT drops below
22µF
0.1µF
1V, BATTLO sinks current. BATTLO is an open-drain
output. In combination with PFI/PFO, this allows moni-
toring of both the input and output voltages.
BATT
PFI
LX
OUT
3.3V
OUT
OUT
Re ve rs e -Ba t t e ry P ro t e c t io n
The MAX1642/MAX1643 can sustain/survive single-cell
battery reversal up to the package power-dissipation
limit. An internal 5Ω resistor in series with a diode limits
reverse current to less than 220mA, which prevents dam-
age to the MAX1642/MAX1643. Prolonged operation
above 220mA reverse-battery current can degrade the
devices’ performance.
0.1µF
22µF
MAX1642
PF0
SHDN
GND
FB
Figure 2. MAX1642 3.3V Standard Application Circuit
________________De s ig n In fo rm a t io n
Ou t p u t Vo lt a g e S e le c t io n
The MAX1642/MAX1643 operate with a 3.3V ±4% or
adjustable output. To select fixed-voltage operation, con-
nect FB to GND. For an adjustable output between 2V
a nd 5.2V, c onne c t FB to a re s is tor volta g e d ivid e r
between OUT and GND (Figure 4). FB regulates to 1.23V.
100µH, 350mA
2/MAX1643
0.88V to 1.65V INPUT
22µF
0.1µF
BATT
LX
3.3V
OUT
OUT
OUT
Since FB leakage is 10nA max, select feedback resistor
R2 in the 100kΩ to 1MΩ range. R1 is given by:
MAX1643
0.1µF 22µF
PFI
V
OUT
R1 = R2
= 1.23V.
- 1
BATTLO
GND
V
REF
PFO
FB
where V
REF
P o w e r-Fa il De t e c t io n
The MAX1642/MAX1643 have an on-chip comparator for
power-fail detection. This comparator can detect loss of
power at the input or output. If the voltage at PFI falls
below 614mV, the PFO output sinks current to GND.
Hysteresis at the power-fail input is 1%. The power-fail
monitor’s threshold is set by two resistors: R3 and R4
(Figure 5). Set the threshold using the following equation:
Figure 3. MAX1643 3.3V Standard Application Circuit
the battery voltage decreases below the start-up volt-
age (see Typical Operating Characteristics).
In d u c t o r S e le c t io n
A 100µH ind uc tor is re c omme nd e d for mos t a p p li-
cations. The use of lower inductor values (down to
68µH) increases maximum output current. Higher val-
ues (up to 220µH) reduce peak inductor current and
consequent ripple and noise. The inductor’s saturation-
current rating must exceed the peak current limit syn-
the s ize d b y the MAX1642/MAX1643’s timing
algorithms:
V
TH
R3 = R4
- 1
V
PFI
where V is the desired threshold of the power-fail
TH
detector, and V is the 614mV reference of the power-
PFI
fail comparator. Since PFI leakage is 10nA max, select
feedback resistor R4 in the 100kΩ to 1MΩ range.
K
MAX
Lo w -Ba t t e ry S t a rt -Up
The MAX1642/MAX1643 are bootstrapped circuits with
a low-voltage start-up oscillator. They can start under
low-load conditions at lower battery voltages than at full
load. Once started, the output can maintain the load as
I
=
PEAK
L
MIN
where K
= 35V-µs. The maximum recommended
is 350mA. For best efficiency, inductor series
resistance should be less than 1Ω.
MAX
I
PEAK
8
_______________________________________________________________________________________
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
Ca p a c it o r S e le c t io n
Choose input and output capacitors to service input
and output peak currents with acceptable voltage rip-
ple. A 22µF, 6V, low-ESR, surface-mount tantalum out-
p ut filte r c a p a c itor typ ic a lly p rovid e s 60mV outp ut
ripple when stepping up from 1.3V to 3.3V at 20mA.
100µH
0.88V to 1.65V INPUT
22µF 0.1µF
V = 2V
OUT
TO 5.2V
BATT
PFI
LX
OUT
The input filter capacitor (C ) also reduces peak cur-
IN
OUT
rents drawn from the battery and improves efficiency.
100pF*
R1
R2
MAX1642
Low equivalent series resistance (ESR) capacitors are
recommended. Capacitor ESR is a major contributor to
output ripple (usually more than 60%). Ceramic capaci-
tors have the lowest ESR, but low-ESR tantalums repre-
sent a good balance between cost and performance.
Low-ESR aluminum electrolytic capacitors are tolerable,
and standard aluminum electrolytic capacitors should
be avoided. Do not exceed tantalum capacitors’ ripple-
current ratings; select capacitors with a rating exceed-
FB
PF0
SHDN
GND
*OPTIONAL COMPENSATION
ing the peak inductor current (I
).
PEAK
Figure 4. Adjustable-Output Circuit
P C Bo a rd La yo u t a n d Gro u n d in g
High switching frequencies and large peak currents
make PC board layout an important part of design. Poor
design can result in excessive EMI on the feedback paths
and voltage gradients in the ground plane. Both of these
factors can result in instability or regulation errors. The
OUT pin must be bypassed directly to GND as close to
the IC as possible (within 0.2 in. or 5mm).
V
TH
MAX1642
MAX1643
R3
R4
PFI
Pla c e p owe r c omp one nts —s uc h a s the MAX1642/
MAX1643, inductor, input filter capacitor, and output filter
capacitor—as close together as possible. Keep their
traces short, direct, and wide (≥50 mil or 1.25mm), and
place their ground pins close together in a star-ground
configuration. Keep the extra copper on the board and
integrate it into ground as a pseudo-ground plane. On
multilayer boards, route the star ground using compo-
nent-side copper fill, then connect it to the internal ground
plane using vias.
Figure 5. Power-Fail Detection Circuit
2) Us e a c los e d -c ore ind uc tor, s uc h a s toroid or
shielded bobbin, to minimize fringe magnetic fields.
3) Choose the largest inductor value that satisfies the
load requirement to minimize peak switching cur-
rent and resulting ripple and noise.
Place the external voltage-feedback network very close to
the FB pin (within 0.2 in. or 5mm). Noisy traces, such as
from the LX pin, should be kept away from the voltage-
feedback network and separated from it using grounded
copper. The evaluation kit manual shows an example PC
board layout, routing, and pseudo-ground plane.
4) Use low-ESR input and output filter capacitors.
5) Follow sound circuit-board layout and grounding
rules (see the PC Board Layout and Grounding
section).
No is e a n d Vo lt a g e Rip p le
EMI and output voltage ripple can be minimized by fol-
lowing a few simple design rules.
6) Where necessary, add LC pi filters, linear post-reg-
ula tors s uc h a s the MAX8863 a nd MAX8864
(SOT23 package), or shielding. The LC pi filter’s
cutoff frequency should be at least a decade or two
below the DC-DC converter’s switching frequency
for the specified load and input voltage.
1) Place the DC-DC converter and digital circuitry on
an opposite corner of the PC board, away from sen-
sitive RF and analog input stages.
_______________________________________________________________________________________
9
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
__________________ Ch ip In fo rm a t io n
Table 1. Component Suppliers
SUPPLIER
PHONE
FAX
TRANSISTOR COUNT: 594
(803) 946-0690
(800) 282-4975
(803) 626-3123
AVX
USA
SUBSTRATE CONNECTED TO GND
Coilcraft
Coiltronics
Dale
USA
USA
USA
(847) 639-6400
(561) 241-7876
(605) 668-4131
(847) 639-1469
(561) 241-9339
(605) 665-1627
USA
Japan
(847) 843-7500
81-7-5231-8461
(847) 843-2798
81-7-5256-4158
Nichicon
USA
Japan
(619) 661-6835
81-7-2070-6306
(619) 661-1055
81-7-2070-1174
Sanyo
Sprague
Sumida
TDK
USA
(603) 224-1961
(603) 224-1430
USA
Japan
(847) 956-0666
81-3-3607-5111
(847) 956-0702
81-3-3607-5144
USA
(847) 390-4373
(847) 390-4428
2/MAX1643
Table 2. Surface-Mount Inductor Information
INDUCTOR SPECIFICATION
INDUCTANCE
VENDOR/PART
(µH)
RESISTANCE
I
SAT
(Ω)
(mA)
400
610
310
520
250
270
400
210
220
350
Coilcraft DO1608-683
0.75
0.46
1.1
68
Sumida CD54-680
Coilcraft DO1608-104
100
Sumida CD54-101
0.7
TDK NLC565050T-101K
Coilcraft DO1608-154
Sumida CD54-151
1.6
1.7
150
220
1.1
TDK NLC565050T-151K
Coilcraft DO1608-224
Sumida CD54-221
2.2
2.3
1.57
10 ______________________________________________________________________________________
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
2/MAX1643
________________________________________________________P a c k a g e In fo rm a t io n
______________________________________________________________________________________ 11
Hig h -Effic ie n c y, S t e p -Up
DC-DC Co n ve rt e rs fo r 1 V In p u t s
NOTES
2/MAX1643
12 ______________________________________________________________________________________
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