_______________General Description
The MAX764/MAX765/MAX766 inverting switching regu-
lators are highly efficient over a wide range of load cur-
rents, delivering up to 1.5W. A unique, current-limited,
pulse-frequency-modulated (PFM) control scheme com-
bines the benefits of traditional PFM converters with the
benefits of pulse-width-modulated (PWM) converters.
Like PWM converters, the MAX764/MAX765/MAX766 are
highly efficient at heavy loads. Yet because they are PFM
devices, they use less than 120µA of supply current (vs.
2mA to 10mA for a PWM device).
The input voltage range is 3V to 16V. The output volt-
age is preset at -5V (MAX764), -12V (MAX765), or -15V
(MAX766); it can also be adjusted from -1V to -16V
using two external resistors (Dual ModeTM). The maxi-
mum operating VIN - VOUT differential is 20V.
These devices use miniature external components; their
high switching frequencies (up to 300kHz) allow for less
than 5mm diameter surface-mount magnetics. A stan-
dard 47µH inductor is ideal for most applications, so no
magnetics design is necessary.
An internal power MOSFET makes the MAX764/MAX765/
MAX766 ideal for minimum component count, low- and
medium-power applications. For increased output drive
capability or higher output voltages, use the
MAX774/MAX775/MAX776 or MAX1774, which drive an
external power P-channel MOSFET for loads up to 5W.
________________________Applications
LCD-Bias Generators
Portable Instruments
LAN Adapters
Remote Data-Acquisition Systems
Battery-Powered Applications
____________________________Features
♦High Efficiency for a Wide Range of Load Currents
♦250mA Output Current
♦120µA Max Supply Current
♦5µA Max Shutdown Current
♦3V to 16V Input Voltage Range
♦-5V (MAX764), -12V (MAX765), -15V (MAX766),
or Adjustable Output from -1V to -16V
♦Current-Limited PFM Control Scheme
♦300kHz Switching Frequency
♦Internal, P-Channel Power MOSFET
______________Ordering Information
Ordering Information continued on last page.
* Dice are tested at T
A
= +25°C, DC parameters only.
**Contact factory for availability and processing to MIL-STD-883.
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
LX
V+
V+
GND
REF
SHDN
FB
OUT
MAX764
MAX765
MAX766
DIP/SO
TOP VIEW
__________________Pin Configuration
GND
MAX764
SHDN
LX
OUT
ON/OFF
REF
47µH
OUTPUT
-5V
INPUT
3V TO 15V V+
FB
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0176; Rev 0; 6/94
PART
MAX764CPA
MAX764CSA
MAX764C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 SO
Dice*
MAX764EPA
MAX764ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
MAX764MJA -55°C to +125°C 8 CERDIP**
MAX765CPA
MAX765CSA
MAX765C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C 8 Plastic DIP
8 SO
Dice*
MAX765EPA
MAX765ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
MAX765MJA -55°C to +125°C 8 CERDIP**
Evaluation Kit
Available
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°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.
V+ to GND..............................................................-0.3V to +17V
OUT to GND...........................................................+0.5V to -17V
Maximum Differential (V+ to OUT) ......................................+21V
REF, SHDN, FB to GND ...............................-0.3V to (V+ + 0.3V)
LX to V+..................................................................+0.3V to -21V
LX Peak Current ...................................................................1.5A
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C) .........................471mW
CERDIP (derate 8.00mW/°C above +70°C) .................640mW
Operating Temperature Ranges
MAX76_C_A ........................................................0°C to +70°C
MAX76_E_A .....................................................-40°C to +85°C
MAX76_MJA ..................................................-55°C to +125°C
Maximum Junction Temperatures
MAX76_C_A/E_A ..........................................................+150°C
MAX76_MJA .................................................................+175°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10sec) ............................+300°C
3V ≤V+ ≤16V
V+ = 16V, SHDN = 0V or V+
V+ = 16V, SHDN < 0.4V
4V ≤V+ ≤6V
0mA ≤ILOAD ≤100mA
MAX76_M
3V ≤V+ ≤16V
MAX76_C/E
0µA ≤IREF ≤100µA
MAX76_M
MAX765C/E, -11.52V ≤VOUT ≤12.48V
MAX764, -4.8V ≤VOUT ≤5.2V
MAX76_E
MAX76_C
MAX76_M
MAX76_E
V+ = 16V, SHDN > 1.6V
V+ = 10V, SHDN > 1.6V
3V ≤V+ ≤16V
MAX766, -14.40V ≤VOUT ≤-15.60V
MAX76_C
MAX765M, -11.52V ≤VOUT ≤12.48V
CONDITIONS
V1.6VIH
SHDN Input Voltage High µA±1SHDN Leakage Current
80 %/V0.12Line Regulation (Note 2) %/mA0.008Load Regulation (Note 2) µV/V40 100REF Line Regulation 415
mV
410
REF Load Regulation
1.4550 1.5 1.5450
1.4625 1.5 1.5375 V
1.4700 1.5 1.5300
VREF
Reference Voltage
35 105
50 120
µA
90 120IS
Supply Current 3.5
V+ V
3.0 16.0
V+ Input Voltage Range
68 120 mA
150 260
IOUT
Output Current and Voltage
(Note 1)
±90
±70
2
ISHDN
Shutdown Current 15
mV-10 10FB Trip Point
nA
±50
IFB
FB Input Current
UNITSMIN TYP MAXSYMBOLPARAMETER
MAX76_C/E
MAX76_M
VOUT = -5V 82VOUT = -15V
Efficiency (Note 2) 10mA ≤ILOAD ≤100mA,
VIN = 5V %
3V ≤V+ ≤16V V0.4VIL
SHDN Input Voltage Low
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
_______________________________________________________________________________________ 3
Note 1: See Maximum Output Current vs. Supply Voltage graph in the
Typical Operating Characteristics
. Guarantees are based on
correlation to switch on-time, switch off-time, on-resistance, and peak current rating.
Note 2: Circuit of Figure 2.
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
IVOUTI+ (V+) ≥10V
ILXI+ (V+) ≤20V
IVOUTI+ (V+) ≥10V
CONDITIONS
µs1.8 2.3 2.8tOFF
Minimum Switch Off-Time µs12 16 20tON
Maximum Switch On-Time A0.5 0.75IPEAK
Peak Current at LX
±30
±10 µA
±5
LX Leakage Current
Ω1.4 2.5LX On-Resistance
UNITSMIN TYP MAXSYMBOLPARAMETER MAX76_C
MAX76_E
MAX76_M
__________________________________________Typical Operating Characteristics
(V+ = 5V, VOUT = -5V, TA= +25°C, unless otherwise noted.)
100
00.1 10 1000
MAX764
EFFICIENCY vs. LOAD CURRENT
MAX764-01
LOAD CURRENT (mA)
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
1 100
CIRCUIT OF FIGURE 2
VOUT = -5V ±4%
V+ = 5V
V+ = 10V
V+ = 15V
100
00.1 10 1000
MAX765
EFFICIENCY vs. LOAD CURRENT
MAX764-02
LOAD CURRENT (mA)
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
1 100
V+ = 8V
V+ = 5V
CIRCUIT OF FIGURE 2
VOUT = -12V ±4%
100
00.1 10 1000
MAX766
EFFICIENCY vs. LOAD CURRENT
MAX764-03
LOAD CURRENT (mA)
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
1 100
V+ = 5V
CIRCUIT OF FIGURE 2
VOUT = -15V ±4%
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(V+ = 5V, VOUT = -5V, TA= +25°C, unless otherwise noted.)
0-60
SHUTDOWN CURRENT
vs. TEMPERATURE
MAX764 -07
TEMPERATURE (°C)
SHUTDOWN CURRENT (µA)
-40 -20 0 20 40 60 80 100 120 140
V+ = 15V
0.5
1.0
1.5
2.0
2.5
3.0
4.0
3.5
V+ = 8V
V+ = 4V 15.0 -60
MAXIMUM SWITCH ON-TIME
vs. TEMPERATURE
MAX764 -08
TEMPERATURE (°C)
MAXIMUM SWITCH ON-TIME (µs)
-40 -20 0 20 40 60 80 100 120 140
V+ = 15V
V+ = 5V
15.2
15.4
15.6
15.8
16.0
16.2
16.4
16.6
16.8
17.0
2.20 -60
MINIMUM SWITCH OFF-TIME
vs. TEMPERATURE
MAX764 -09
TEMPERATURE (°C)
MINIMUM SWITCH OFF-TIME (µs)
-40 -20 0 20 40 60 80 100 120 140
2.25
2.30
2.35
2.40
2.45
2.50
2.60
2.55
V+ = 5V
V+ = 15V
6.2 -60
SWITCH ON/OFF-TIME RATIO
vs. TEMPERATURE
MAX764 -10
TEMPERATURE (°C)
SWITCH ON/OFF-TIME RATIO (µs/µs)
-40 -20 0 20 40 60 80 100 120 140
V+ = 5V
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
7.1
7.2
0
START-UP SUPPLY VOLTAGE
vs. OUTPUT CURRENT
MAX764 -11
OUTPUT CURRENT (mA)
START-UP SUPPLY VOLTAGE (V)
0
1
2
3
4
5
6
8
7
50 100 150 200 250 300
CIRCUIT OF FIGURE 2 10,000
120
LX LEAKAGE CURRENT
vs. TEMPERATURE
10
100
MAX764-12
TEMPERATURE (°C)
LX LEAKAGE CURRENT (nA)
1000
30 40 50 60 70 80 90 100 110 120 130
IVOUTI + (V+) = 20V
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAX764 -04
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
3
600
4 5 6 7 8 9 10 11 12 13 14 15 16
500
400
300
200
100
0
VOUT = -5V
VOUT = -12V
VOUT = -15V
CIRCUIT OF FIGURE 2
60
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX764 -05
SUPPLY VOLTAGE (V)
NO-LOAD SUPPLY CURRENT (µA)
3
65
70
75
80
85
90
100
95
4 5 6 7 8 9 10 11 12 13 14 15 16 50 -60
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
55
MAX764 -06
TEMPERATURE (°C)
NO-LOAD SUPPLY CURRENT (µA)
-40 -20 0 20 40 60 80 100 120 140
60
65
70
75
80
85
90
95
100
105
110
V+ = 15V
V+ = 5V
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
_______________________________________________________________________________________
5
1000
0.01 0 2 4 6 10 12 14816
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
0.1
MAX764-17
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
1
10
100 ILOAD = 100mA
ILOAD = 0mA
CIRCUIT OF FIGURE 2
-60
REFERENCE OUTPUT RESISTANCE
vs. TEMPERATURE
MAX764 -15
TEMPERATURE (°C)
REFERENCE OUTPUT RESISTANCE (Ω)
-40 -20 0 20 40 60 80 100 120 140
0
50
100
150
200
250
IREF = 10µA
IREF = 50µA
IREF = 100µA
____________________________Typical Operating Characteristics (continued)
(V+ = 5V, VOUT = -5V, TA= +25°C, unless otherwise noted.)
0.8 -60
LX ON-RESISTANCE
vs. TEMPERATURE
MAX764 -13
TEMPERATURE (°C)
LX ON-RESISTANCE (Ω)
-40 -20 0 20 40 60 80 100 120 140
IVOUTI + (V+) = 10V
1.0
1.2
1.4
1.6
1.8
2.0
2.2
IVOUTI + (V+) = 15V
IVOUTI + (V+) = 20V
-60
PEAK CURRENT AT LX
vs. TEMPERATURE
MAX764
-
14
TEMPERATURE (°C)
CURRENT AT LX (A)
-40 -20 0 20 40 60 80 100 120 14
0
0.65
0.70
0.75
0.80
0.85
0.90
0.95
IVOUTI + (V+) = 20V
IVOUTI + (V+) = 15V
IVOUTI + (V+) = 10V
-60
REFERENCE OUTPUT
vs. TEMPERATURE
MAX764 -16
TEMPERATURE (°C)
REFERENCE OUTPUT (V)
-40 -20 0 20 40 60 80 100 120 140
1.506
1.504
1.502
1.500
1.498
1.496
1.494
1.492
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
6 _______________________________________________________________________________________
CIRCUIT OF FIGURE 2, VOUT = -5V, ILOAD = 100mA
A: VOUT, 50mV/div, AC-COUPLED
B: V+, 5V TO 10V, 5V/div
5ms/div
LINE-TRANSIENT RESPONSE
A
B
0V
CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 140mA
A: OUTPUT RIPPLE, 100mV/div
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
5µs/div
DISCONTINUOUS CONDUCTION AT
HALF AND FULL CURRENT LIMIT
A
B
0A
C
0V
CIRCUIT OF FIGURE 2, V+ = 5V, ILOAD = 100mA, VOUT = -5V
A: VOUT, 2V/div
B: SHUTDOWN PULSE, 0V TO 5V, 5V/div
2ms/div
TIME TO ENTER/EXIT SHUTDOWN
A
B
0V
0V
CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V
A: VOUT, 50mV/div, AC-COUPLED
B: ILOAD, 0mA TO 100mA, 100mA/div
5ms/div
LOAD-TRANSIENT RESPONSE
A
B
0mA
____________________________Typical Operating Characteristics (continued)
(V+ = 5V, VOUT = -5V, TA= +25°C, unless otherwise noted.)
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
_______________________________________________________________________________________ 7
CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 80mA
A: OUTPUT RIPPLE, 100mV/div
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
5µs/div
DISCONTINUOUS CONDUCTION AT
HALF CURRENT LIMIT
A
B
0A
C
0V
CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 240mA
A: OUTPUT RIPPLE, 100mV/div
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
5µs/div
CONTINUOUS CONDUCTION AT
FULL CURRENT LIMIT
A
B
0A
C
0V
______________________________________________________________Pin Description
GroundGND5
Positive Power-Supply Input. Must be tied together. Place a 0.1µF input bypass capacitor as close to
the V+ and GND pins as possible.
V+6, 7
Drain of the Internal P-Channel Power MOSFET. LX has a peak current limit of 0.75A.LX8
1.5V Reference Output that can source 100µA for external loads. Bypass to ground with a 0.1µF capacitor.REF4
Active-High Shutdown Input. With SHDN high, the part is in shutdown mode and the supply current is less
than 5µA. Connect to ground for normal operation.
SHDN3
PIN
Feedback Input. Connect FB to REF to use the internal voltage divider for a preset output. For adjustable-
output operation, use an external voltage divider, as described in the section
Setting the Output Voltage.
FB2
Sense Input for Fixed-Output Operation (VFB = VREF). OUT must be connected to VOUT.OUT1
FUNCTIONNAME
____________________________Typical Operating Characteristics (continued)
(V+ = 5V, VOUT = -5V, TA= +25°C, unless otherwise noted.)
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
8 _______________________________________________________________________________________
_______________Detailed Description
Operating Principle
The MAX764/MAX765/MAX766 are BiCMOS, inverting,
switch-mode power supplies that provide fixed outputs
of -5V, -12V, and -15V, respectively; they can also be
set to any desired output voltage using an external
resistor divider. Their unique control scheme combines
the advantages of pulse-frequency modulation (pulse
skipping) and pulse-width modulation (continuous puls-
ing). The internal P-channel power MOSFET allows
peak currents of 0.75A, increasing the output current
capability over previous pulse-frequency-modulation
(PFM) devices. Figure 1 shows the MAX764/MAX765/
MAX766 block diagram.
The MAX764/MAX765/MAX766 offer three main
improvements over prior solutions:
1) They can operate with miniature (less than 5mm
diameter) surface-mount inductors, because of their
300kHz switching frequency.
2) The current-limited PFM control scheme allows efficien-
cies exceeding 80% over a wide range of load currents.
3) Maximum quiescent supply current is only 120µA.
Figures 2 and 3 show the standard application circuits
for these devices. In these configurations, the IC is
powered from the total differential voltage between the
input (V+) and output (VOUT). The principal benefit of
this arrangement is that it applies the largest available
signal to the gate of the internal P-channel power MOS-
FET. This increased gate drive lowers switch on-resis-
tance and increases DC-DC converter efficiency.
Since the voltage on the LX pin swings from V+ (when the
switch is ON) to IVOUTIplus a diode drop (when the
MAX764
MAX765
MAX766
P
TRIG Q
ONE-SHOT
TRIGQ ONE-SHOT
S
R
Q
CURRENT
CONTROL CIRCUITS
1.5V
REFERENCE
N
FROM OUT
FROM V+
FROM V+
0.1V
(HALF
CURRENT)
0.2V
(FULL
CURRENT)
GND
LX
V+
OUT
V+
REF
SHDN ERROR
COMPARATOR
COMPARATOR
CURRENT
COMPARATOR
FB
Figure 1. Block Diagram
switch is OFF), the range of input and output voltages is
limited to a 21V absolute maximum differential voltage.
When output voltages more negative than -16V are
required, substitute the MAX764/MAX765/MAX766 with
Maxim’s MAX774/MAX775/MAX776 or MAX1774, which
use an external switch.
PFM Control Scheme
The MAX764/MAX765/MAX766 use a proprietary, cur-
rent-limited PFM control scheme that blends the best
features of PFM and PWM devices. It combines the
ultra-low supply currents of traditional pulse-skipping
PFM converters with the high full-load efficiencies of
current-mode pulse-width modulation (PWM) convert-
ers. This control scheme allows the devices to achieve
high efficiencies over a wide range of loads, while the
current-sense function and high operating frequency
allow the use of miniature external components.
As with traditional PFM converters, the internal power
MOSFET is turned on when the voltage comparator
senses that the output is out of regulation (Figure 1).
However, unlike traditional PFM converters, switching is
accomplished through the combination of a peak cur-
rent limit and a pair of one-shots that set the maximum
on-time (16µs) and minimum off-time (2.3µs) for the
switch. Once off, the minimum off-time one-shot holds
the switch off for 2.3µs. After this minimum time, the
switch either 1) stays off if the output is in regulation, or
2) turns on again if the output is out of regulation.
The MAX764/MAX765/MAX766 limit the peak inductor
current, which allows them to run in continuous-con-
duction mode and maintain high efficiency with heavy
loads. (See the photo Continuous Conduction at Full
Current Limit in the
Typical Operating Characteristics
.)
This current-limiting feature is a key component of the
control circuitry. Once turned on, the switch stays on
until either 1) the maximum on-time one shot turns it off
(16µs later), or 2) the current limit is reached.
To increase light-load efficiency, the current limit is set to
half the peak current limit for the first two pulses. If those
pulses bring the output voltage into regulation, the volt-
age comparator holds the MOSFET off and the current
limit remains at half the peak current limit. If the output
voltage is still out of regulation after two pulses, the cur-
rent limit is raised to its 0.75A peak for the next pulse.
(See the photo Discontinuous Conduction at Half and Full
Current Limit in the
Typical Operating Characteristics
.)
Shutdown Mode
When SHDN is high, the MAX764/MAX765/MAX766
enter a shutdown mode in which the supply current
drops to less than 5µA. In this mode, the internal biasing
circuitry (including the reference) is turned off and OUT
discharges to ground. SHDN is a TTL/CMOS-logic level
input. Connect SHDN to GND for normal operation.
With a current-limited supply, power-up the device while
unloaded or in shutdown mode (hold SHDN high until V+
exceeds 3.0V) to save power and reduce power-up cur-
rent surges. (See the Supply Current vs. Supply Voltage
graph in the
Typical Operating Characteristics
.)
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
_______________________________________________________________________________________ 9
MAX764
MAX765
MAX766
SHDN
REF
LX
V+
GND
FB VOUT
V+
OUT
C4
68µF
20V
D1
1N5817
L1
47µH
8
6
7
3
4
2
1
C3
0.1µF
C2
0.1µF
C1
120µF
20V
VIN
MAX764
MAX765
MAX766
-5
-12
-15
3 to 15
3 to 8
3 to 5
PRODUCT OUTPUT
VOLTAGE (V) INPUT
VOLTAGE (V)
5
Figure 2. Fixed Output Voltage Operation
MAX764
MAX765
MAX766
SHDN
REF
LX
V+
GND
FB VOUT
-1V to
-16V
V+
OUT
C4
68µF
20V
D1
1N5817
L1
47µH
8
6
7
3
4
2
1
C3
0.1µF
C2
0.1µF
C1
120µF
20V
VIN
5
R2
R1
Figure 3. Adjustable Output Voltage Operation
MAX764/MAX765/MAX766
Modes of Operation
When delivering high output currents, the MAX764/
MAX765/MAX766 operate in continuous-conduction
mode. In this mode, current always flows in the induc-
tor, and the control circuit adjusts the duty-cycle of the
switch on a cycle-by-cycle basis to maintain regulation
without exceeding the switch-current capability. This
provides excellent load-transient response and high
efficiency.
In discontinuous-conduction mode, current through the
inductor starts at zero, rises to a peak value, then
ramps down to zero on each cycle. Although efficiency
is still excellent, the output ripple may increase slightly.
__________________Design Procedure
Setting the Output Voltage
The MAX764/MAX765/MAX766’s output voltage can be
adjusted from -1.0V to -16V using external resistors R1
and R2, configured as shown in Figure 3. For
adjustable-output operation, select feedback resistor
R1 = 150kΩ. R2 is given by:
VOUT
R2 = (R1)
I
———
I
VREF
where VREF = 1.5V.
For fixed-output operation, tie FB to REF.
Inductor Selection
In both continuous- and discontinuous-conduction
modes, practical inductor values range from 22µH to
68µH. If the inductor value is too low, the current in the
coil will ramp up to a high level before the current-limit
comparator can turn off the switch, wasting power and
reducing efficiency. The maximum inductor value is not
critical. A 47µH inductor is ideal for most applications.
For highest efficiency, use a coil with low DC resis-
tance, preferably under 100mΩ. To minimize radiated
noise, use a toroid, pot core, or shielded coil.
Inductors with a ferrite core or equivalent are recom-
mended. The inductor’s incremental saturation-current
rating should be greater than the 0.75A peak current
limit. It is generally acceptable to bias the inductor into
saturation by approximately 20% (the point where the
inductance is 20% below the nominal value).
Table 1 lists inductor types and suppliers for various
applications. The listed surface-mount inductors’ effi-
ciencies are nearly equivalent to those of the larger-
size through-hole inductors.
Diode Selection
The MAX764/MAX765/MAX766’s high switching fre-
quency demands a high-speed rectifier. Use a
Schottky diode with a 0.75A average current rating,
such as the 1N5817 or 1N5818. High leakage currents
may make Schottky diodes inadequate for high-temper-
ature and light-load applications. In these cases you
can use high-speed silicon diodes, such as the
MUR105 or the EC11FS1. At heavy loads and high
temperatures, the benefits of a Schottky diode’s low for-
ward voltage may outweigh the disadvantages of its
high leakage current.
Capacitor Selection
Output Filter Capacitor
The primary criterion for selecting the output filter
capacitor (C4) is low effective series resistance (ESR).
The product of the inductor-current variation and the
output filter capacitor’s ESR determines the amplitude
of the high-frequency ripple seen on the output voltage.
A 68µF, 20V Sanyo OS-CON capacitor with ESR =
45mΩ(SA series) typically provides 50mV ripple when
converting from 5V to -5V at 150mA.
Output filter capacitor ESR also affects efficiency. To
obtain optimum performance, use a 68µF or larger,
low-ESR capacitor with a voltage rating of at least
20V. The smallest low-ESR surface-mount tantalum
capacitors currently available are from the Sprague
595D series. Sanyo OS-CON series organic semi-
conductors and AVX TPS series tantalum capacitors
also exhibit very low ESR. OS-CON capacitors are
particularly useful at low temperatures. Table 1 lists
some suppliers of low-ESR capacitors.
For best results when using capacitors other than those
suggested in Table 1 (or their equivalents), increase
the output filter capacitor’s size or use capacitators in
parallel to reduce ESR.
Input Bypass Capacitor
The input bypass capacitor, C1, reduces peak currents
drawn from the voltage source and reduces the amount
of noise at the voltage source caused by the switching
action of the MAX764–MAX766. The input voltage
source impedance determines the size of the capacitor
required at the V+ input. As with the output filter
capacitor, a low-ESR capacitor is highly recommended.
For output currents up to 250mA, a 100µF to 120µF
capacitor with a voltage rating of at least 20V (C1) in
parallel with a 0.1µF capacitor (C2) is adequate in most
applications. C2 must be placed as close as possi-
ble to the V+ and GND pins.
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
10 ______________________________________________________________________________________
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
______________________________________________________________________________________ 11
Table 1. Component Suppliers
PRODUCTION METHOD INDUCTORS CAPACITORS DIODES
Surface Mount
Matsuo
267 series
Sprague
595D/293D series
AVX
TPS series
Nihon
EC10QS02L (Schottky)
EC11FS1 (high-speed silicon)
Miniature Through-Hole Sumida
RCH895 series Sanyo
OS-CON series (very low ESR)
Low-Cost Through-Hole Renco
RL1284 series Nichicon
PL series
Motorola
1N5817, 1N5818, (Schottky)
MUR105 (high-speed silicon)
Sumida
CD75/105 series
Coiltronics
CTX series
Coilcraft
DT/D03316 series
Reference Capacitor
Bypass REF with a 0.1µF capacitor (C3). The REF out-
put can source up to 100µA for external loads.
Layout Considerations
Proper PC board layout is essential to reduce noise
generated by high current levels and fast switching
waveforms. Minimize ground noise by connecting
GND, 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, trace resistance, and radiat-
ed noise. In particular, keep the traces connected to
FB and LX short. C2 must be placed as close as pos-
sible to the V+ and GND pins. If an external resistor
divider is used (Figure 3), the trace from FB to the resis-
tors must be extremely short.
SUPPLIER PHONE FAX
AVX USA: (803) 448-9411 (803) 448-1943
Coilcraft USA: (708) 639-6400 (708) 639-1469
Coiltronics USA: (407) 241-7876 (407) 241-9339
Matsuo USA: (714) 969-2491
Japan: 81-6-337-6450 (714) 960-6492
81-6-337-6456
Motorola USA: (800) 521-6274 (602) 952-4190
Nichicon USA: (708) 843-7500
Japan: 81-7-5231-8461 (708) 843-2798
81-7-5256-4158
Renco USA: (516) 586-5566 (516) 586-5562
Sanyo OS-CON USA: (619) 661-6835
Japan: 81-7-2070-1005 (619) 661-1055
81-7-2070-1174
Sprague Electric Co. USA: (603) 224-1961 (603) 224-1430
Nihon USA: (805) 867-2555
Japan: 81-3-3494-7411 (805) 867-2556
81-3-3494-7414
Sumida USA: (708) 956-0666
Japan: 81-3-3607-5111 (708) 956-0702
81-3-3607-5144
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.
12
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX764/MAX765/MAX766
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Q
DC-DC Inverters
_Ordering Information (continued) ___________________Chip Topography
GND
V+
V+
OUT
FB
SHDN
REF
LX
0.145"
(3683µm)
0.080"
(2032µm)
TRANSISTOR COUNT: 443
SUBSTRATE CONNECTED TO V+
PART
MAX766CPA
MAX766CSA
MAX766C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 SO
Dice*
MAX766EPA
MAX766ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
MAX766MJA -55°C to +125°C 8 CERDIP**
* Dice are tested at T
A
= +25°C, DC parameters only.
**Contact factory for availability and processing to MIL-STD-883.
Mouser Electronics
Authorized Distributor
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MAX765EPA+ MAX765ESA+T MAX766CSA+T MAX766EPA+ MAX766ESA+T MAX764CSA-T MAX764ESA-T
MAX765CSA-T MAX765EPA MAX765ESA-T MAX766CSA MAX766CSA-T MAX764CPA MAX764ESA
MAX765CPA MAX765CSA MAX765ESA MAX766ESA MAX766ESA-T
