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PDF MAX1626-MAX1627 Data sheet ( Hoja de datos )
| Número de pieza | MAX1626-MAX1627 | |
| Descripción | 5V/3.3V or Adjustable / 100% Duty-Cycle / High-Efficiency / Step-Down DC-DC Controllers | |
| Fabricantes | Maxim Integrated | |
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19-1075; Rev 0; 6/96
EVFAOLLULAOTWIOSNDKAITTAMSAHNEUEATL
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
_______________General Description
The MAX1626/MAX1627 step-down DC-DC switching
controllers provide high efficiency over loads ranging
from 1mA to more than 2A. A unique current-limited,
pulse-frequency-modulated (PFM) control scheme
operates with up to a 100% duty cycle, resulting in very
low dropout voltages. This control scheme eliminates
minimum load requirements and reduces the supply
current under light loads to 90µA (versus 2mA to 10mA
for common pulse-width modulation controllers).
These step-down controllers drive an external P-chan-
nel MOSFET, allowing design flexibility for applications
to 12W or higher. Soft-start reduces current surges dur-
ing start-up. A high switching frequency (up to 300kHz)
and operation in continuous-conduction mode allow the
use of tiny surface-mount inductors. Output capacitor
requirements are also reduced, minimizing PC board
area and system costs.
The output voltage is preset at 5V or 3.3V for the
MAX1626 and adjustable for the MAX1627. Input volt-
ages can be up to 16.5V. The MAX1626/MAX1627 are
functional upgrades for the MAX1649/MAX1651.
____________________________Features
o Low Dropout Voltage
o 100% Maximum Duty Cycle
o Soft-Start Limits Start-Up Current
o Efficiency >90% (3mA to 2A Loads)
o Output Power >12.5W
o 90µA Max Quiescent Current
o 1µA Max Shutdown Current
o Up to 300kHz Switching Frequency
o 16.5V Max Input Voltage
o Output Voltage: 5V/3.3V (MAX1626)
Adjustable (MAX1627)
o Current-Limited Control Scheme
______________Ordering Information
________________________Applications
PCMCIA Power Supplies
Personal Digital Assistants
Hand-Held Computers
Portable Terminals
Low-Cost Notebook Computer Supplies
5V to 3.3V Green PC Applications
High-Efficiency Step-Down Regulation
Minimum-Component DC-DC Converters
Battery-Powered Applications
__________________Pin Configuration
TOP VIEW
OUT 1
3/5 (FB) 2
SHDN 3
REF 4
MAX1626
MAX1627
8 GND
7 EXT
6 CS
5 V+
( ) ARE FOR MAX1627
SO
PART
TEMP. RANGE
MAX1626C/D
0°C to +70°C
MAX1626ESA
-40°C to +85°C
MAX1627C/D
MAX1627ESA
0°C to +70°C
-40°C to +85°C
* Dice are tested at TA = +25°C.
PIN-PACKAGE
Dice*
8 SO
Dice*
8 SO
__________Typical Operating Circuit
INPUT
3.3V to 16.5V
ON/OFF
V+
MAX1626
SHDN
CS
EXT
3/5
REF OUT
GND
P
OUTPUT
3.3V
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
1 page  
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
1.310
REFERENCE OUTPUT VOLTAGE
vs. TEMPERATURE
1.305
1.300
IREF = 0µA
IREF = 10µA
1.295
1.290
1.285
IREF = 50µA
IREF = 100µA
1.280
-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
MAX1626 SHUTDOWN RESPONSE TIME
AND SUPPLY CURRENT
A
B
C
500µs/div
V+ = 8V, VOUT = 5V, LOAD = 1A
A: OUT, 2V/div
B: SUPPLY CURRENT, 1A/div
C: SHDN, 5V/div
MAX1626 LOAD-TRANSIENT RESPONSE
MAX1626 LINE-TRANSIENT RESPONSE
A
A
B
B
100µs/div
V+ = 8V, VOUT = 3.3V, LOAD = 30mA to 2A
A: OUT, 50mV/div, 3.3V DC OFFSET
B: LOAD CURRENT, 1A/div
5ms/div
VOUT = 5V, LOAD = 1A, CIN = 33µF
A: OUT, 100mV/div, 5V DC OFFSET
B: V+ 6V to 12V, 2V/div
LINE-TRANSIENT RESPONSE
FROM 100% DUTY CYCLE
A
B
5ms/div
VOUT = 3.3V, LOAD = 1A, CIN = 47µF
A: OUT, 100mV/div, 3.3V DC OFFSET
B: V+ 3.3V to 15V, 5V/div
_______________________________________________________________________________________ 5
5 Page 
5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
Table 2. Component Suppliers
COMPANY
AVX USA
Coilcraft
Coiltronics
Dale
International
Rectifier
IRC
Motorola
Nichicon
Nihon
Sanyo
USA
USA
USA
USA
USA
USA
USA
Japan
USA
Japan
USA
Japan
Siliconix
USA
Sprague
Sumida
United
Chemi-Con
USA
USA
Japan
USA
PHONE
(803) 946-0690
or
(800) 282-4975
(847) 639-6400
(516) 241-7876
(605) 668-4131
(310) 322-3331
(512) 992-7900
(602) 303-5454
(847) 843-7500
81-7-5231-8461
(805) 867-2555
81-3-3494-7411
(619) 661-6835
81-7-2070-6306
(408) 988-8000
or
(800) 554-5565
(603) 224-1961
(847) 956-0666
81-3-3607-5111
(714) 255-9500
FAX
(803) 626-3123
(847) 639-1469
(516) 241-9339
(605) 665-1627
(310) 322-3332
(512) 992-3377
(602) 994-6430
(847) 843-2798
81-7-5256-4158
(805) 867-2698
81-3-3494-7414
(619) 661-1055
81-7-2070-1174
(408) 970-3950
(603) 224-1430
(847) 956-0702
81-3-3607-5144
(714) 255-9400
Diode Selection
The MAX1626/MAX1627’s high switching frequency
demands a high-speed rectifier. Schottky diodes, such
as the 1N5817–1N5822 family or surface-mount equiva-
lents, are recommended. Ultra-high-speed rectifiers
with reverse recovery times around 50ns or faster, such
as the MUR series, are acceptable. Make sure that the
diode’s peak current rating exceeds the peak current
limit set by RSENSE, and that its breakdown voltage
exceeds V+. Schottky diodes are preferred for heavy
loads due to their low forward voltage, especially in
low-voltage applications. For high-temperature applica-
tions, some Schottky diodes may be inadequate due to
their high leakage currents. In such cases, ultra-high-
speed rectifiers are recommended, although a Schottky
diode with a higher reverse voltage rating can often
provide acceptable performance.
Capacitor Selection
Choose filter capacitors to service input and output
peak currents with acceptable voltage ripple.
Equivalent series resistance (ESR) in the capacitor is a
major contributor to output ripple, so low-ESR capaci-
tors are recommended. Sanyo OS-CON capacitors are
best, and low-ESR tantalum capacitors are second
best. Low-ESR aluminum electrolytic capacitors are tol-
erable, but do not use standard aluminum electrolytic
capacitors.
Voltage ripple is the sum of contributions from ESR and
the capacitor value:
VRIPPLE ≈ VRIPPLE,ESR + VRIPPLE,C
To simplify selection, assume initially that two-thirds of
the ripple results from ESR and one-third results from
capacitor value. Voltage ripple as a consequence of
ESR is approximated by:
VRIPPLE,ESR ≈ (RESR)(IPEAK)
Estimate input and output capacitor values for given
voltage ripple as follows:
CIN
=
1
2
LI2∆L
VRIPPLE,CINVIN
COUT
=
1
2
LI2∆L
VRIPPLE,COUTVOUT
VIN
VIN
− VOUT
where I∆L is the change in inductor current (around
0.5IPEAK under moderate loads).
These equations are suitable for initial capacitor selec-
tion; final values should be set by testing a prototype or
evaluation kit. When using tantalum capacitors, use
good soldering practices to prevent excessive heat
from damaging the devices and increasing their ESR.
Also, ensure that the tantalum capacitors’ surge-current
ratings exceed the start-up inrush and peak switching
currents.
Pursuing output ripple lower than the error compara-
tor’s hysteresis (0.5% of the output voltage) is not prac-
tical, since the MAX1626/MAX1627 will switch as
needed, until the output voltage crosses the hysteresis
threshold. Choose an output capacitor with a working
voltage rating higher than the output voltage.
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on V+ and CS, caused by the circuit’s switching
action. Use a low-ESR capacitor. Two smaller-value
low-ESR capacitors can be connected in parallel for
lower cost. Choose input capacitors with working volt-
age ratings higher than the maximum input voltage.
Place a surface-mount ceramic capacitor very close to
V+ and GND, as shown in Figure 7. This capacitor
bypasses the MAX1626/MAX1627, and prevents spikes
and ringing on the power source from obscuring the
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX1626-MAX1627.PDF ] | |
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