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PDF MAX742 Data sheet ( Hoja de datos )
| Número de pieza | MAX742 | |
| Descripción | Switch-Mode Regulator with +5V to 12V or 15V Dual Output | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-3105; Rev 2; 8/96
EVFAOLLULAOTWIOSNDKAITTAMSAHNEUEATL
Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
_______________General Description
The MAX742 DC-DC converter is a controller for dual-out-
put power supplies in the 3W to 60W range. Relying on
simple two-terminal inductors rather than transformers, the
MAX742 regulates both outputs independently to within
±4% over all conditions of line voltage, temperature, and
load current.
The MAX742 has high efficiency (up to 92%) over a wide
range of output loading. Two independent PWM current-
mode feedback loops provide tight regulation and opera-
tion free from subharmonic noise. The MAX742 can
operate at 100kHz or 200kHz, so it can be used with small
and lightweight external components. Also ripple and
noise are easy to filter. The MAX742 provides a regulated
output for inputs ranging from 4.2V to 10V (and higher with
additional components).
External power MOSFETs driven directly from the MAX742
are protected by cycle-by-cycle overcurrent sensing. The
MAX742 also features undervoltage lockout, thermal shut-
down, and programmable soft-start.
If 3W of load power or less is needed, refer to the MAX743
data sheet for a device with internal power MOSFETs.
________________________Applications
DC-DC Converter Module Replacement
Distributed Power Systems
Computer Peripherals
__________________Pin Configuration
TOP VIEW
FB+ 1
CC+ 2
AGND 3
AV 4
100/200 5
12/15 6
VREF 7
SS 8
CC- 9
FB- 10
MAX742
20 CSH+
19 CSL+
18 GND
17 EXT+
16 PUMP
15 PDRV
14 EXT-
13 V+
12 CSH-
11 CSL-
DIP/SO
____________________________Features
o Specs Guaranteed for In-Circuit Performance
o Load Currents to ±2A
o 4.2V to 10V Input-Voltage Range
o Switches From ±15V to ±12V Under Logic Control
o ±4% Output Tolerance Max Over Temp, Line,
and Load
o 90% Typ Efficiency
o Low-Noise, Current-Mode Feedback
o Cycle-by-Cycle Current Limiting
o Undervoltage Lockout and Soft-Start
o 100kHz or 200kHz Operation
______________Ordering Information
PART
TEMP. RANGE
MAX742CPP
0°C to +70°C
MAX742CWP
0°C to +70°C
MAX742C/D
0°C to +70°C
MAX742EPP
-40°C to +85°C
MAX742EWP
-40°C to +85°C
MAX742MJP
-55°C to +125°C
* Contact factory for dice specifications
PIN-PACKAGE
20 Plastic DIP
20 Wide SO
Dice*
20 Plastic DIP
20 Wide SO
20 CERDIP
__________Simplified Block Diagram
MAX742
CC-
+5V
INPUT
+2.0V
VREF
CC+
R -SENSE
PWM
S -DRIVE
OSC
S +DRIVE
PWM
R +SENSE
P
N
-VO
+VO
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
1 page  
Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, ILOAD = 100mA, unless otherwise noted.)
SWITCHING WAVEFORMS,
INVERTING SECTION
SWITCHING WAVEFORMS,
STEP-UP SECTION
A
A
B
B
2µs/div
A = GATE DRIVE, 5V/div
B = SWITCH VOLTAGE, 10V/div
C = SWITCH CURRENT, 0.2A/div
C
2µs/div
A = GATE DRIVE, 5V/div
B = SWITCH VOLTAGE, 10V/div
C = SWITCH CURRENT, 0.2A/div
C
OUTPUT-VOLTAGE NOISE,
FILTERED AND UNFILTERED
A
B
2µs/div
A = NOISE WITH i FILTER, 1mV/div
B = NOISE WITHOUT FILTER, 20mV/div
MEASURED AT -VOUT
V+ = 5V
BW = 5MHz
LOAD-TRANSIENT RESPONSE
A = +VO, 20mV/div
B = -VO, 50mV/div
200µs/div
A
B
_______________________________________________________________________________________ 5
5 Page 
Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
where:
VSW is the voltage drop across the the switch transistor
and current-sense resistor in the on state (0.3V typ).
VD is the rectifier forward voltage drop (0.4V typ).
LIR is the ratio of peak-to-peak ripple current to DC
offset current in the inductor (0.5 typ).
Current-Sense Resistor Value
The current-sense resistor values are calculated accord-
ing to the worst-case-low current-limit threshold voltage
from the Electrical Characteristics table and the peak
inductor current. The peak inductor current calculations
that follow are also useful for sizing the switches and
specifying the inductor current saturation ratings.
150mV
RSENSE = ————
IPEAK
ILOAD (VOUT + VD)
+IPEAK (boost) = ————————— +
VIN - VSW
(VIN - VSW) (VOUT + VD - VIN)
—————————————
(2)(F)(L)(VOUT + VD)
ILOAD (VOUT + VD+ VIN)
+IPEAK (inverting) = ———————————— +
VIN - VSW
(VIN - VSW) (VOUT + VD + VIN)
—————————————
(2)(F)(L) (VOUT + VD)
Filter Capacitor Value
The output filter capacitor values are generally deter-
mined by the effective series resistance (ESR) and volt-
age rating requirements rather than actual capacitance
requirements for loop stability. In other words, the
capacitor that meets the ESR requirement for noise pur-
poses nearly always has much more output capaci-
tance than is required for AC stability. Output voltage
noise is dominated by ESR and can be roughly calcu-
lated by an Ohm’s Law equation:
VNOISE (peak-to-peak) = IPEAK x RESR
where VNOISE is typically 0.15V.
Ensure the output capacitors selected meet the follow-
ing minimum capacitance requirements:
Minimum CF = 60µF per output or the following, whichev-
er is greater:
CF = 0.015/RLOAD (in Farads, ±15V mode)
CF = 0.01/RLOAD
(in Farads, ±12V mode)
Compensation Capacitor (CC) Value
The compensation capacitors (CC+ and CC-) cancel
the zero introduced by the output filter capacitors’ ESR,
improving phase margin, and AC stability. The com-
pensation poles set by CC+ and CC- should be set to
match the ESR zero frequencies of the output filter
capacitors according to the following:
RESR x CF
CC (in Farads) = —————— (use 1000pF minimum)
10kΩ
Standard 6W Application
The 6W supply (Figure 2) generates ±200mA at ±15V,
or ±250mA at ±12V. Output capability is increased to
10W or more by heatsinking the power FETs, using
cores with higher current capability (such as Gowanda
#050AT1003), and using higher filter capacitance.
Ferrite and MPP inductor cores optimize efficiency and
size. Iron-power toroids designed for high frequencies
are economical, but larger.
Ripple is directly proportional to filter capacitor equiva-
lent series resistance (ESR). In addition, about 250mV
transient noise occurs at the LX switch transitions. A
very short scope probe ground lead or a shielded
enclosure is need for making accurate measurements
of transient noise. Extra filtering, as shown in Figure 2,
reduces both noise components.
High-Power 22W Application
The 22W application circuit (Figure 3) generates ±15V
at ±750mA or ±12V at ±950mA. Noninductive wire-
wound resistors with Kelvin current-sensing connec-
tions replace the metal-film resistors of the previous
(6W) circuit. Gate drive for the P-channel FET is boot-
strapped from the negative supply via diode D6. The
2.7V zener (D5) is required in 15V mode to prevent
overvoltage. The charge pump (D3, D4, and C6) may
not be necessary if the circuit is lightly loaded
(<100mA) on start-up. AIE part #415-0963 is a ferrite
pot-core inductor that can be used in place of a small-
er, more expensive moly-permalloy toroid inductor (L1,
L2). Higher efficiencies can be achieved by adding
extra MOSFETs in parallel. Load levels above 10W
make it necessary to add heatsinks, especially to the P-
channel FET.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX742.PDF ] | |
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