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 over all conditions of line voltage temperature and load current

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Description

Niveau: Secondaire, Lycée, Terminale
_______________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 _________________________

  • load current

  • noise without

  • applications dc-dc

  • dual output

  • pump

  • charge-pump load

  • duty-cycle limit


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Informations

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19-3105; Rev 2; 8/96

Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
_______________General Description____________________________Features
The MAX742 DC-DC converter is a controller for dual-out-
©
Specs Guaranteed for In-Circuit Performance
put power supplies in the 3W to 60W range. Relying on
©
Load Currents to ±2A
simple two-terminal inductors rather than transformers, the
©
4.2V to 10V Input-Voltage Range
MAX742 regulates both outputs independently to within
±4% over all conditions of line voltage, temperature, and
©
Switches From ±15V to ±12V Under Logic Control
load current.
©
±4% Output Tolerance Max Over Temp, Line,
The MAX742 has high efficiency (up to 92%) over a wide
and Load
range of output loading. Two independent PWM current-
©
90% Typ Efficiency
mode feedback loops provide tight regulation and opera-
©
Low-Noise, Current-Mode Feedback
tion free from subharmonic noise. The MAX742 can
©
Cycle-by-Cycle Current Limiting
operate at 100kHz or 200kHz, so it can be used with small
©
Undervoltage Lockout and Soft-Start
and lightweight external components. Also ripple and
noise are easy to filter. The MAX742 provides a regulated
©
100kHz or 200kHz Operation
output for inputs ranging from 4.2V to 10V (and higher with
______________Ordering Information
additional components).
External power MOSFETs driven directly from the MAX742
PARTTEMP. RANGEPIN-PACKAGE
are protected by cycle-by-cycle overcurrent sensing. The
MAX742
CPP0°C to +70°C20 Plastic DIP
MAX742 also features undervoltage lockout, thermal shut-
MAX742CWP0°C to +70°C20 Wide SO
down, and programmable soft-start.
MAX742C/D0°C to +70°CDice*
If 3W of load power or less is needed, refer to the MAX743
MAX742EPP-40°C to +85°C20 Plastic DIP
data sheet for a device with internal power MOSFETs.
MAX742EWP-40°C to +85°C20 Wide SO
MAX742MJP-55°C to +125°C20 CERDIP
________________________Applications
* Contact factory for dice specifications
DC-DC Converter Module Replacement
__________Simplified Block Diagram
Distributed Power Systems
V5+Computer Peripherals
INPUT
MAX742
-CC__________________Pin Configuration
TOP VIEW

FB+120CSH+
CC+219CSL+
AGND318GND
AV417EXT+
100/2005
MAX742
16PUMP
12/15615PDRV
VREF714EXT-
SS813V+
CC-912CSH-
FB-1011CSL-
DIP/SO

+V2R.E0FV

+CC

R-SENSE
MWPS-DRIVEP
CSOS+DRIVEN
MWPR+SENSE

OV-OV+

________________________________________________________________Maxim Integrated Products1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
ABSOLUTE MAXIMUM RATINGS
V+, AV+ to AGND, GND.........................................-0.3V to +12VContinuous Power Dissipation (any package)
PDRV to V+.............................................................+0.3V to -14Vup to +70°C.....................................................................500mW
FB+, FB- to GND..................................................................±25Vderate above +70°C by..........................................100mW/°C
Input Voltage to GNDOperating Temperature Ranges
(CC+, CC-, CSH+, CSL+, CSH-, CSL-,MAX742C_ _.......................................................0°C to +70°C
SS, 100/200, 12/15)..................................-0.3V to (V+ + 0.3V)MAX742E_ _....................................................-40°C to +85°C
Output Voltage to GNDMAX742MJP..................................................-55°C to +125°C
(EXT+, PUMP)..........................................-0.3V to (V+ + 0.3V)Storage Temperature Range.............................-65°C to +150°C
EXT- to PDRV................................................-0.3V to (V+ + 0.3V)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
(Circuit of Figure 2, +4.5V < V+ < +5.5V.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Output Voltage, ±15V Mode0mA < I
L
< 100mA, T
A
= +25°C14.5515.45V
(Notes 1, 2)12/15= 0VT
A
= T
MIN
to T
MAX
14.4015.60
Output Voltage, ±12V Mode0mA < I
L
< 125mA, T
A
= +25°C11.6412.36V
(Notes 1, 2)12/15= V+T
A
= T
MIN
to T
MAX
11.5212.48

ELECTRICAL CHARACTERISTICS
(Circuit of Figure 2, V+ = 5V, 100/200= 12/15= 0V; T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONS
Line RegulationV+ = 4.5V to 5.5V, PDRV from PUMP
Load Regulation (Note 2)I
LOAD
= 0mA to 100mA
No EXT- or PUMP load,V+ = 5V
No-Load Supply CurrentFB+ = FB- = open circuitV+ = 10V
Undervoltage LockoutUVLO
Undervoltage Lockout Hysteresis
Reference Output Voltage
Oscillator Frequencyf
OSC
100/200= 0V
100/200= V+
PUMP Frequency
Duty-Cycle Limit (Note 3)EXT+ or EXT-
Positive Current-Limit ThresholdCSL+ = 0V, FB+ = open circuit
(CSH+ to CSL+)
Negative Current-Limit ThresholdCSH- = V+, FB- = open circuit
(CSH- to CSL-)

MINTYPMAXUNITS
0.010.05%/%
30100mV
3Am013.84.2V
2.0V0.2V170200230kHz
75100125
f
OSC
/2kHz
0958%150225300mV
150225300mV

2_______________________________________________________________________________________

Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 2, V+ = 5V, 100/200= 12/15= 0V; T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Output Voltage HighV
OH
EXT+, EXT-, I
L
= 1mA, V+ = 4.5V, PDRV= -3V4.3V
Output Voltage LowV
OL
EXT+, EXT-, I
L
= -1mA, V+ = 4.5V, PDRV= -3V-2.8V
Output Sink CurrentTV+ == +4.255V°,C PDRV = -3V,EXT+ = 4.5V100200mA
A
EXT- = 4.5V200350
Output Source CurrentTV+ == +4.255V°,C PDRV = -3V,EXT+ = 0V-200-100mA
A
EXT- = -3V-350-200
EXT+, C
LOAD
= 2nF70
Output Rise/Fall TimeEXT-, C
LOAD
= 4nF, PDRV = -3V100ns
PUMP Output Voltage (Note 4)V+ = 4.5V, I
L
= -5mA, T
A
= +25°C-3V
Compensation Pin ImpedanceCC+, CC-10k
½
Thermal-Shutdown Threshold190°C
Soft-Start Source CurrentSS = 0V37µA
Soft-Start Sink CurrentV+ = 3.8V, SS = 2V-2-0.5mA
Note 1:
TDheev icaebisli tayr teo 1d0r0iv%e tleosatdesd utpo ttoh e1sAe ilsi mgitusa ruanndteere d0 mbyA ttho e1 c0u0rrmeAn ta-linmd itt ot h1r2e5shmoAld c, oonutdiptiuot nssw iunsign, ga nadu ttohme aotiuct pteuts t ceuqrrueinptment.
source/sink tests. See Figures 2 and 3.
Note 2:
Actual load capability of the circuit of Figure 2 is ±200mA in ±15V mode and ±250mA in ±12V mode. Load regulation is
Note 3:
tGeustaerad natte leodw bery lidmeistisg dn.ue to test equipment limitations.
Note 4:
Measured at Point A, circuit of Figure 2, with PDRV disconnected.

_______________________________________________________________________________________3

Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, V+ = 5V, T
A
= +25°C, unless otherwise noted.)
UNDERVOLTAGE LOCKOUT HYSTERESISCHARGE-PUMP LOAD REGULATIONPDRV CURRENT vs. C
EXT-
25-5.06
2±0105kVH zM OMDOED, EMEASURED AT POINT APPUDRMVP FDOIRSCCEODN NTEO C-T4EV D
20-4.55
415-4.0V+ = 5V200kHz
310-3.5
2LOCKOUT
5ENABLED-3.0V+ = 4.5V100kHz
1 -2.5
0123456012345678910 01234
SUPPLY VOLTAGE (V)CHARGE-PUMP LOAD CURRENT (mA)CAPACITANCE AT EXT- (nF)
EFFICIENCY vs. LOAD CURRENT, EFFICIENCY vs. LOAD CURRENT, EFFICIENCY vs. LOAD CURRENT,
22W CIRCUIT, ±15V MODE6W CIRCUIT, ±15V MODE6W CIRCUIT, ±12V MODE
9090100kHz90100kHz
100kHz
8080200kHz80200kHz
200kHz
707070
ICNIRDCUUCITT OORFS F=I GGUORWE A3N, DA 121-AT2502
60 (MPP CORE), 6060
Q2 = TWO IRF9Z30 IN PARALLEL I N D U C T O R S = (GMOPWP ACNODRAE )050-AT1003 I N D U C T O R S = (GMOPWP ACNODRAE )050-AT1003
±15V MODE
50 50 50
0±200±400±600±800±10000±50±100±150±200±2500±75±150±225±300
LOAD CURRENT (mA)LOAD CURRENT (mA)LOAD CURRENT (mA)
PEAK INDUCTOR CURRENT vs. CURRENT-LIMIT THRESHOLD vs.
LOAD CURRENTSOFT-START VOLTAGE
1200100kHz
00111000200
900200kHz
800150
007006500100
004003200MEASURED AT LX-, 50
100±15V MODE
0501001502000123
LOAD CURRENT (mA)SOFT-START VOLTAGE (V)
4_______________________________________________________________________________________

Switch-Mode Regulator with
+5V to ±12V or ±15V Dual Output
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, I
LOAD
= 100mA, unless otherwise noted.)
SWIINTVCEHIRNTIGN WG ASVEECFTIOORNMS, SWITSCTHEIPN-GU P WSAEVCETFIOONRMS,
AA

2
m
s/div
A = GATE DRIVE, 5V/div
CB == SSWWIITTCCHH VCOULRTRAEGNET,, 10.02VA//ddivi v

FOILUTTEPRUETD- VAONLDT UANGFEI LNTOEISREE, D

2
m
s/div
A = NOISE WITH i FILTER, 1mV/div
B = NOISE WITHOUT FILTER, 20mV/div
MEASURED AT -V
OUT
V+ = 5V
BW = 5MHz

A

B

B

C

2
m
s/div
A = GATE DRIVE, 5V/div
BC == SSWWIITTCCHH VCOULRTRAEGNET, , 10.02VA//ddivi v

LOAD-TRANSIENT RESPONSE

A = +VO, 20mV/div
B = -VO, 50mV/div

200
m
s/div

B

C

AB

_______________________________________________________________________________________5

+S5wVit tcoh -±M1o2dVe oRr e±g1u5lVa tDoru awl itOhutput

______________________________________________________________Pin Description
PINNAMEFUNCTION
1FB+Step-Up Feedback Input
2CC+Step-Up Compensation Capacitor
3AGNDAnalog Ground
4AV+Analog Supply Voltage Input (+5V)
5100/200Selects oscillator frequency. Ground for 200kHz, or tie to V+ for 100kHz.
612/15Selects V
OUT
. Ground for ±15V, or tie to V+ for ±12V.
7VREFReference Voltage Output (+2.00V). Force to GND or V+ to disable chip.
8SSSoft-Start Timing Capacitor (sources 5µA)
9CC-Inverting Compensation Capacitor
10FB-Inverting Section Feedback Input
11CSL-Current-Sense Low (inverting section)
12CSH-Current-Sense High (inverting section)
13V+Supply Voltage Input (+5V)
14EXT-Push-Pull Output—drives external P-channel MOSFET.
15PDRVVoltage Input—negative supply for P-channel MOSFET driver.
16PUMPCharge-Pump Driver—clock output at 1/2 oscillator frequency.
17EXT+Push-Pull Output—drives external logic-level N-channel MOSFET.
18GNDHigh-Current Ground
19CSL+Current-Sense Low (step-up section)
20CSH+Current-Sense High (step-up section)

________________Operating Principle
source currents reach a trip threshold determined by
Each current-mode controller consists of a summingthe output-voltage error signal. This creates a duty-
amplifier that adds three signals: the current waveformcycle modulated pulse train at the oscillator frequency,
where the on time is proportional to both the output-
from the power switch FET, an output-voltage error sig-voltage error signal and the peak inductor current. Low
nal, and a ramp signal for AC compensation generated
by the oscillator. The output of the summing amplifierpeak currents or high output-voltage error signals result
resets a flip-flop, which in turn activates the power FETin a high duty cycle (up to 90% maximum).
driver stage (Figure 1).AC stability is enhanced by the internal ramp signal
applied to the error amplifier. This scheme eliminates
Both external transistor switches are synchronized toregenerative “staircasing” of the inductor current, which
the oscillator and turn on simultaneously when the flip-
flop is set. The switches turn off individually when theiris otherwise a problem when in continuous current
mode with greater than 50% duty cycle.

6_______________________________________________________________________________________

DNGAFERV/2151

+BF

FERV

+5V tSo w±it1c2hV- Moro d±e1 5RVe gDuulaalt oOru twpituht

CC+100/200AV+

MAX742

QRSESLUPSOFT-START
S1E2L/E1C5 TRAMPOSCAND THERMAL
SHUTDOWN
SQUARETO V+
SQR

+HSC

+LSCV++TXEDNGSSPMUP-TXEVRDP-HSC

-LSC

FB-CC-
Figure1. MAX742 Detailed Block Diagram
_______________Detailed Description
Charge-Pump Voltage Inverter
The charge-pump (PUMP) output is a rail-to-rail square
100kHz/200kHz Oscillator
wave at half the oscillator frequency. The square wave
The MAX742 oscillator frequency is generated withoutdrives an external diode-capacitor circuit to generate a
external components and can be set at 100kHz ornegative DC voltage (Point A in Figure 2), which in turn
200kHz by pin strapping. Operating the device atbiases the inverting-output drive stage via PDRV. The
100kHz results in lower supply current and improvedcharge pump thus increases the gate-source voltage
efficiency, particularly with light loads. However, com-applied to the external P-channel FET. The low on-
ponent stresses increase and noise becomes more dif-resistance resulting from increased gate drive ensures
ficult to filter. For a given inductor value, the lowerhigh efficiency and guarantees start-up under heavy
operating frequency results in slightly higher peak cur-loads. If a -5V to -8V supply is already available, it can
rents in the inductor and switch transistor (see Typicalbe tied directly to PDRV and all of the charge-pump
Operating Characteristics, Peak Inductor Current vs.components removed. For input voltages greater than
Load Current graph). When the lower frequency is used8V, ground PDRV to prevent overvoltage. Observe
in conjunction with an LC-type output filter (optionalPDRV absolute maximum ratings.
components in Figure 2), larger component values are
required for equivalent filtering.
_______________________________________________________________________________________7

+S5wVit tcoh -±M1o2dVe oRr e±g1u5lVa tDoru awl itOhutput

NIV4.5V to 6V*
100R
W
1

100
m
L1H

3LD125
m
H
Q1150
m
CF8 150
m
CF9 2.2C
m
1F4
C1 OPTIONAL
10.1
m
FC2 FB+CSH+0.16R
W
2
3.3nFCC+CSL+
NOTES:

AGND
MAX742
GNDQQ12 == MMoottoorroollaa MMTTPP1152NP0055 L
L1, L2 = MAXL001
AV+EXT+C6D3D4DC18,– DC21 2= =1 NM5A8X17C 001
J1100/200PUMPRD23,, RD34 == RFCujDi ERRSAF 812A- 0M04e toalr F1ilNm5 8±137 %
12/15PDRV1
m
FL3, L4 = Wilco MFB 250
POINT
10
m
C3F VREFEXT-1
m
CF7 A
C4SSV+C10 C13
3.3nCF5 CC-CSH-R3 150
m
FD0.I1S
m
C F CERAMIC
W1.0FB-CSL-
Q225L
m
4 H
L2 D2150C
m
1F1 150C
m
1F2 2.2C
m
1F5
mH001OPTIONAL

* SFUOPR PHLIYG-HVEORL TINAPGUE TR VAONLGTEA SGEE,C TSIEOE N.
Figure 2. Standard 6W Application Circuit

8_______________________________________________________________________________________

V+O

OV-

NIV4.5V to 6V*
100R
W
1

+5V tSo w±it1c2hV- Moro d±e1 5RVe gDuulaalt oOr utwpituht

31CmF03325
m
LH1 D1
1N5820
OV+Q11000
m
CF8 1C09 00
m
F
NOTES:

Q1 = Motorola MTP25N06L
LQ12, =L 2I n=t erGnoawtiaonndaal R1e2c1tiAfiTe2r 5I0R2FV9CZ 30
R2, R3 = KRL LB4-1 ±3%
C8–C13 = Nichicon PL Series (25V or 35V)

1C0.1
m
F1FB+CSH+R2
C2 0.02
W
6.8nFCC+CSL+
AGND
MAX742
GND
AV+EXT+C61ND941 4
100/200PUMP
3D1J12/15PDRV1
m
F1N914
10
m
CF3 VREFEXT-C7
C4 SSV+1
m
F
2.2
m
FC10
6.8nCF5 CC-CSH-R3 1000
m
F
0.02
W
10V
FB-CSL-0.C11
m
4 F
DISC CERAMIC
2QD2 C11 C12
L2 1N58201000
m
F1000
m
F
mH52

* SFOURP PHLIYG-HVEORL ITNAPGUET RVAONLGTEA SGEE,C TSIEOE N.
Figure 3. High-Power 22W Application Circuit

-OV

_______________________________________________________________________________________9

+S5wVit tcoh -±M1o2dVe oRr e±g1u5lVa tDoru awl itOhutput

Supply-Voltage Range
Although designed for operation from a +5V logic
supply, the MAX742 works well from 4.2V (the upper
limit of the undervoltage lockout threshold) to +10V
(absolute maximum rating plus a safety margin). The
upper limit can be further increased by limiting the
voltage at V+ with a zener shunt or series regulator.
To ensure AC stability, the inductor value should be
scaled linearly with the nominal input voltage. For
example, if Figure 3’s application circuit is powered
from a nominal 9V source, the inductor value should be
increased to 40µH or 50µH. At high input voltages
(>8V), the charge pump can cause overvoltage at
PDRV. If the input can exceed 8V, ground PDRV and
remove the capacitors and diodes associated with the
charge pump.
In-Circuit Testing for
Guaranteed Performance
Figure 2’s circuit has been tested at all extremes of line,
load, and temperature. Refer to the Electrical
Characteristicstable for guaranteed in-circuit specifica-
tions. Successful use of this circuit requires no compo-
nent calculations.
Soft-Start
A capacitor connected between Soft-Start (SS) and
ground limits surge currents at power-up. As shown in
the Typical Operating Characteristics, the peak switch
current limit is a function of the voltage at SS. SS is
internally connected to a 5µA current source and is
diode-clamped to 2.6V (Figure 8). Soft-start timing is
therefore set by the SS capacitor value. As the SS volt-
age ramps up, peak inductor currents rise until they
reach normal operating levels. Typical values for the SS
capacitor, when it is required at all, are in the range of
1µF to 10µF.
Fault Conditions Enabling SS Reset
In addition to power-up, the soft-start function is enabled
by a variety of fault conditions. Any of the following con-
ditions will cause an internal pull-down transistor to dis-
charge the SS capacitor, triggering a soft-start cycle:
Undervoltage lockout
Thermal shutdown
VREF shorted to ground or supply
VREF losing regulation

V5+5
m
A
MAX742
V2+REFERENCE
SS8TO CURRENT–
EXTERNAL LIMIT COMPARATOR
SSCAPACITORNFAULT

Figure 4. Soft-Start Equivalent Circuit
__________________Design Procedure
Inductor Value
An exact inductor value isn’t critical. The inductor value
can be varied in order to make tradeoffs between
noise, efficiency, and component sizes. Higher inductor
values result in continuous-conduction operation, which
maximizes efficiency and minimizes noise. Physically
smallest inductors (where E = 1/2 LI
2
is minimum) are
realized when operating at the crossover point between
continuous and discontinuous modes. Lowering the
inductor value further still results in discontinuous cur-
rent even at full load, which minimizes the output
capacitor size required for AC stability by eliminating
the right-half-plane zero found in boost and inverting
topologies. Ideal current-mode slope compensation
where m = 2 x V/L is achieved if L (Henries) = R
SENSE
(
½
) x 0.001, but again the exact value isn’t critical and
the inductor value can be adjusted freely to improve
AC performance. The following equations are given for
continuous-conduction operation since the MAX742 is
mainly intended for low-noise analog power supplies.
See Appendix A in Maxim’s Battery Management and
DC-DC Converter Circuit Collectionfor crossover point
and discontinuous-mode equations.
Boost (positive) output:
(V
IN
- V
SW
)
2
(V
OUT
+ V
D
- V
IN
)
L = ———————————————
(V
OUT
+ V
D
)
2
(I
LOAD
)(F)(LIR)
Inverting (negative) output:
(V
IN
- V
SW
)
2
L = —————————————
(V
OUT
+ V
D
)(I
LOAD
)(F)(LIR)

10______________________________________________________________________________________