MAX765ESA-T [MAXIM]
Switching Regulator, Current-mode, 1.5A, 300kHz Switching Freq-Max, BICMOS, PDSO8, 0.150 INCH, PLASTIC, SOIC-8;
| 型号： | MAX765ESA-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switching Regulator, Current-mode, 1.5A, 300kHz Switching Freq-Max, BICMOS, PDSO8, 0.150 INCH, PLASTIC, SOIC-8 |
| 文件： | 总12页 (文件大小：134K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0176; Rev 0; 6/94
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
♦ High Efficiency for a Wide Range of Load Currents
♦ 250mA Output Current
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).
♦ 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
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-
♦ Current-Limited PFM Control Scheme
♦ 300kHz Switching Frequency
♦ Internal, P-Channel Power MOSFET
mum operating V - V
differential is 20V.
IN
OUT
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.
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
8 SO
MAX764CPA
MAX764CSA
MAX764C/D
MAX764EPA
MAX764ESA
MAX764MJA
MAX765CPA
MAX765CSA
MAX765C/D
MAX765EPA
MAX765ESA
MAX765MJA
0°C to +70°C
0°C to +70°C
Dice*
An internal power MOSFET makes the MAX764/MAX765/
MAX766 ideal for minimum component count, low- and
medium-power applications. For increased output drive
c a p a b ility or hig he r outp ut volta g e s , us e the
MAX774/MAX775/MAX776 or MAX1774, which drive an
external power P-channel MOSFET for loads up to 5W.
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 Plastic DIP
8 SO
8 CERDIP**
8 Plastic DIP
8 SO
0°C to +70°C
________________________Ap p lic a t io n s
LCD-Bias Generators
0°C to +70°C
Dice*
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
8 SO
Portable Instruments
LAN Adapters
8 CERDIP**
Remote Data-Acquisition Systems
Battery-Powered Applications
Ordering Information continued on last page.
* Dice are tested at T = +25°C, DC parameters only.
A
**Contact factory for availability and processing to MIL-STD-883.
__________________P in Co n fig u ra t io n
__________Typ ic a l Op e ra t in g Circ u it
INPUT
3V TO 15V
TOP VIEW
V+
OUTPUT
-5V
LX
OUT
FB
LX
1
2
3
4
8
7
6
5
MAX764
47µH
V+
MAX764
MAX765
MAX766
SHDN
ON/OFF
SHDN
REF
V+
GND
OUT
REF
FB
DIP/SO
GND
________________________________________________________________ Maxim Integrated Products
1
Ca ll t o ll fre e 1 -8 0 0 -9 9 8 -8 8 0 0 fo r fre e s a m p le s o r lit e ra t u re .
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
ABSOLUTE MAXIMUM RATINGS
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
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
Continuous Power Dissipation (T = +70°C)
A
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
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+ = 5V, I
= 0mA, C
= 0.1µF, T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.)
MAX A
LOAD
REF
A
MIN
PARAMETER
V+ Input Voltage Range
Supply Current
SYMBOL
CONDITIONS
MIN
3.0
TYP
MAX UNITS
MAX76_C/E
MAX76_M
16.0
V
V+
3.5
I
S
V+ = 16V, SHDN < 0.4V
V+ = 16V, SHDN > 1.6V
V+ = 10V, SHDN > 1.6V
3V ≤ V+ ≤ 16V
90
2
120
µA
5
Shutdown Current
FB Trip Point
I
SHDN
45/MAX76
1
-10
10
mV
MAX76_C
±50
±70
±90
FB Input Current
I
FB
MAX76_E
nA
MAX76_M
MAX764, -4.8V ≤ V
≤ 5.2V
150
68
260
120
120
105
1.5
1.5
1.5
4
OUT
MAX765C/E, -11.52V ≤ V
≤ 12.48V
≤ 12.48V
OUT
Output Current and Voltage
(Note 1)
I
mA
OUT
MAX765M, -11.52V ≤ V
50
OUT
MAX766, -14.40V ≤ V
≤ -15.60V
35
OUT
MAX76_C
MAX76_E
MAX76_M
1.4700
1.4625
1.4550
1.5300
1.5375
1.5450
10
Reference Voltage
V
REF
V
MAX76_C/E
MAX76_M
REF Load Regulation
0µA ≤ I
≤ 100µA
mV
REF
4
15
REF Line Regulation
3V ≤ V+ ≤ 16V
0mA ≤ I
40
100
µV/V
%/mA
%/V
Load Regulation (Note 2)
Line Regulation (Note 2)
≤ 100mA
0.008
0.12
80
LOAD
4V ≤ V+ ≤ 6V
V
= -5V
OUT
10mA ≤ I
≤ 100mA,
LOAD
Efficiency (Note 2)
%
V
IN
= 5V
V
OUT
= -15V
82
SHDN Leakage Current
SHDN Input Voltage High
SHDN Input Voltage Low
V+ = 16V, SHDN = 0V or V+
3V ≤ V+ ≤ 16V
±1
µA
V
V
1.6
IH
V
IL
3V ≤ V+ ≤ 16V
0.4
V
2
_______________________________________________________________________________________
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, I
= 0mA, C
= 0.1µF, T = T
to T , unless otherwise noted. Typical values are at T = +25°C.)
MAX A
LOAD
REF
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MAX76_C
MIN
TYP
MAX UNITS
±5
LX Leakage Current
MAX76_E
MAX76_M
±10
±30
2.5
µA
ILX + (V+) ≤ 20V
I
LX On-Resistance
Peak Current at LX
1.4
0.75
16
Ω
A
IV
I
+ (V+) ≥ 10V
+ (V+) ≥ 10V
OUT
I
0.5
12
IV
I
PEAK
OUT
Maximum Switch On-Time
Minimum Switch Off-Time
t
20
µs
µs
ON
t
1.8
2.3
2.8
OFF
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.
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(V+ = 5V, V
= -5V, T = +25°C, unless otherwise noted.)
A
OUT
MAX764
MAX765
MAX766
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
100
90
100
90
100
90
V+ = 8V
V+ = 5V
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
V+ = 5V
V+ = 5V
V+ = 10V
V+ = 15V
CIRCUIT OF FIGURE 2
V
OUT
CIRCUIT OF FIGURE 2
±
CIRCUIT OF FIGURE 2
±
±
= -5V 4%
V
OUT
= -12V 4%
V
= -15V 4%
OUT
0.1
1
10
100
1000
0.1
1
10
100
1000
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
_______________________________________________________________________________________
3
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
____________________________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 )
(V+ = 5V, V
= -5V, T = +25°C, unless otherwise noted.)
A
OUT
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
110
105
600
100
95
CIRCUIT OF FIGURE 2
= -5V
100
95
500
400
300
V+ = 15V
V+ = 5V
V
OUT
90
85
80
75
70
90
85
80
75
70
65
200
100
0
V
OUT
= -12V
60
55
50
65
60
V
OUT
= -15V
3
4
5
6
7
8
9
10 11 12 13 14 15 16
3
4
5
6
7
8
9
10 11 12 13 14 15 16
-60 -40 -20
0
20 40 60 80 100 120 140
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SHUTDOWN CURRENT
vs. TEMPERATURE
MINIMUM SWITCH OFF-TIME
vs. TEMPERATURE
MAXIMUM SWITCH ON-TIME
vs. TEMPERATURE
4.0
3.5
2.60
2.55
17.0
16.8
16.6
16.4
16.2
16.0
15.8
15.6
15.4
15.2
15.0
45/MAX76
3.0
2.5
2.0
1.5
1.0
2.50
2.45
2.40
2.35
2.30
V+ = 15V
V+ = 15V
V+ = 15V
V+ = 8V
V+ = 5V
V+ = 5V
0.5
0
2.25
2.20
V+ = 4V
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0 20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
SWITCH ON/OFF-TIME RATIO
vs. TEMPERATURE
START-UP SUPPLY VOLTAGE
vs. OUTPUT CURRENT
LX LEAKAGE CURRENT
vs. TEMPERATURE
10,000
1000
100
8
7
7.2
7.1
7.0
6.9
6.8
6.7
6.6
6.5
6.4
6.3
6.2
CIRCUIT OF FIGURE 2
IVOUTI + (V+) = 20V
6
5
4
3
2
V+ = 5V
10
1
0
1
-60 -40 -20
0
20 40 60 80 100 120 140
0
50
100 150
200 250
300
20 30 40 50 60 70 80 90 100 110 120 130
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
4
_______________________________________________________________________________________
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
____________________________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 )
(V+ = 5V, V
= -5V, T = +25°C, unless otherwise noted.)
A
OUT
LX ON-RESISTANCE
vs. TEMPERATURE
PEAK CURRENT AT LX
vs. TEMPERATURE
REFERENCE OUTPUT RESISTANCE
vs. TEMPERATURE
2.2
2.0
250
200
0.95
0.90
IVOUTI + (V+) = 10V
I
= 10µA
IVOUTI + (V+) = 20V
REF
1.8
1.6
0.85
150
100
50
IVOUTI + (V+) = 15V
IVOUTI + (V+) = 15V
0.80
0.75
I
= 50µA
REF
1.4
1.2
0.70
0.65
1.0
0.8
IVOUTI + (V+) = 10V
I
= 100µA
REF
IVOUTI + (V+) = 20V
0
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
REFERENCE OUTPUT
vs. TEMPERATURE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1.506
1.504
1.502
1.500
1000
I
= 100mA
LOAD
100
10
1
1.498
1.496
I
= 0mA
LOAD
0.1
1.494
CIRCUIT OF FIGURE 2
1.492
0.01
-60 -40 -20
0
20 40 60 80 100 120 140
0
2
4
6
8
10 12 14 16
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
____________________________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 )
(V+ = 5V, V
= -5V, T = +25°C, unless otherwise noted.)
A
OUT
TIME TO ENTER/EXIT SHUTDOWN
LOAD-TRANSIENT RESPONSE
0V
A
A
B
B
0mA
0V
2ms/div
5ms/div
CIRCUIT OF FIGURE 2, V+ = 5V, I
= 100mA, V = -5V
CIRCUIT OF FIGURE 2, V+ = 5V, V = -5V
OUT
LOAD
OUT
A: V , 2V/div
OUT
A: V , 50mV/div, AC-COUPLED
OUT
B: SHUTDOWN PULSE, 0V TO 5V, 5V/div
B: I , 0mA TO 100mA, 100mA/div
LOAD
45/MAX76
DISCONTINUOUS CONDUCTION AT
HALF AND FULL CURRENT LIMIT
LINE-TRANSIENT RESPONSE
A
A
B
B
C
0A
0V
0V
5µs/div
5ms/div
CIRCUIT OF FIGURE 2, V = -5V, I
CIRCUIT OF FIGURE 2, V+ = 5V, V = -5V, I = 140mA
LOAD
= 100mA
LOAD
OUT
OUT
A: OUTPUT RIPPLE, 100mV/div
A: V , 50mV/div, AC-COUPLED
OUT
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
B: V+, 5V TO 10V, 5V/div
6
_______________________________________________________________________________________
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
____________________________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 )
(V+ = 5V, V
= -5V, T = +25°C, unless otherwise noted.)
A
OUT
DISCONTINUOUS CONDUCTION AT
HALF CURRENT LIMIT
CONTINUOUS CONDUCTION AT
FULL CURRENT LIMIT
A
B
A
B
0A
0V
0A
0V
C
C
5µs/div
5µs/div
CIRCUIT OF FIGURE 2, V+ = 5V, V = -5V, I
= 80mA
CIRCUIT OF FIGURE 2, V+ = 5V, V = -5V, I
= 240mA
OUT
LOAD
OUT
LOAD
A: OUTPUT RIPPLE, 100mV/div
A: OUTPUT RIPPLE, 100mV/div
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
B: INDUCTOR CURRENT, 500mA/div
C: LX WAVEFORM, 10V/div
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
Sense Input for Fixed-Output Operation (V = V ). OUT must be connected to V
1
OUT
.
OUT
FB
REF
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.
2
3
FB
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.
SHDN
4
5
REF
1.5V Reference Output that can source 100µA for external loads. Bypass to ground with a 0.1µF capacitor.
Ground
GND
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.
6, 7
8
V+
LX
Drain of the Internal P-Channel Power MOSFET. LX has a peak current limit of 0.75A.
_______________________________________________________________________________________
7
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
FB
COMPARATOR
MAX764
MAX765
REF
MAX766
SHDN
ERROR
COMPARATOR
OUT
V+
V+
N
1.5V
REFERENCE
Q
TRIG
ONE-SHOT
FROM V+
S
Q
P
CURRENT
COMPARATOR
FROM OUT
TRIG
ONE-SHOT
Q
R
LX
45/MAX76
0.2V
0.1V
(FULL
CURRENT)
(HALF
CURRENT)
CURRENT
CONTROL CIRCUITS
FROM V+
GND
Figure 1. Block Diagram
1) They can operate with miniature (less than 5mm
diameter) surface-mount inductors, because of their
300kHz switching frequency.
_______________De t a ile d De s c rip t io n
Op e ra t in g P rin c ip le
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.
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 (V ). The principal benefit of
OUT
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.
The MAX764/MAX765/MAX766 offe r thre e ma in
improvements over prior solutions:
Since the voltage on the LX pin swings from V+ (when the
switch is ON) to
V
plus a diode drop (when the
I OUTI
8
_______________________________________________________________________________________
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
switch is OFF), the range of input and output voltages is
limited to a 21V absolute maximum differential voltage.
P FM Co n t ro l S c h e m e
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.
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.
V
IN
7
1
3
V+
OUT
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.
C2
0.1µF
C1
120µF
20V
MAX764
MAX765
MAX766
6
8
SHDN
V+
LX
2
4
D1
FB
1N5817
V
OUT
REF
C4
68µF
20V
GND
5
L1
47µH
C3
0.1µF
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.
OUTPUT
VOLTAGE (V)
INPUT
VOLTAGE (V)
PRODUCT
MAX764
MAX765
MAX766
-5
3 to 15
3 to 8
3 to 5
-12
-15
Figure 2. Fixed Output Voltage Operation
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.)
V
IN
C1
C2
0.1µF
120µF
20V
7
6
1
3
2
V+
OUT
SHDN
FB
R2
MAX764
MAX765
MAX766
V+
LX
V
-1V to
-16V
OUT
S h u t d o w n Mo d e
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.)
8
D1
1N5817
R1
C3
4
REF
C4
GND
5
L1
47µH
68µF
20V
0.1µF
Figure 3. Adjustable Output Voltage Operation
_______________________________________________________________________________________
9
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
Mo d e s o f Op e ra t io n
Dio d e S e le c t io n
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.
The MAX764/MAX765/MAX766’s high switching fre-
q ue nc y d e ma nd s a hig h-s p e e d re c tifie r. Us e 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
c a n us e hig h-s p e e d s ilic on d iod e s , s uc h a s 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.
In discontinuous-conduction mode, current through the
ind uc tor s ta rts a t ze ro, ris e s to a p e a k va lue , the n
ramps down to zero on each cycle. Although efficiency
is still excellent, the output ripple may increase slightly.
Ca p a c it o r S e le c t io n
__________________De s ig n P ro c e d u re
Output Filter Capacitor
The p rima ry c rite rion for s e le c ting the outp ut filte r
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 Sa nyo OS-CON c a p a c itor with ESR =
45mΩ (SA series) typically provides 50mV ripple when
converting from 5V to -5V at 150mA.
S e t t in g t h e Ou t p u t Vo lt a g e
The MAX764/MAX765/MAX766’s output voltage can be
adjusted from -1.0V to -16V using external resistors R1
a nd R2, c onfig ure d a s s hown in Fig ure 3. For
adjustable-output operation, select feedback resistor
R1 = 150kΩ. R2 is given by:
V
OUT
R2 = (R1) ———
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.
V
REF
I
I
45/MAX76
where V
= 1.5V.
REF
For fixed-output operation, tie FB to REF.
In d u c t o r S e le c t io n
In b oth c ontinuous - a nd d is c ontinuous -c ond uc tion
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 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.
For highest efficiency, use a coil with low DC resis-
tance, preferably under 100mΩ. To minimize radiated
nois e , us e a toroid , p ot c ore , or s hie ld e d c oil.
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).
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
a c tion of the MAX764–MAX766. The inp ut volta g e
source impedance determines the size of the capacitor
re q uire d a t the V+ inp ut. As with the outp ut filte r
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.
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.
10 ______________________________________________________________________________________
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
45/MAX76
Reference Capacitor
Bypass REF with a 0.1µF capacitor (C3). The REF out-
put can source up to 100µA for external loads.
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.
La yo u t Co n s id e ra t io n s
Proper PC board layout is essential to reduce noise
generated by high current levels and fast switching
wa ve forms . Minimize g round nois e b y c onne c ting
GND, the input bypass capacitor ground lead, and the
Table 1. Component Suppliers
PRODUCTION METHOD
INDUCTORS
CAPACITORS
DIODES
Matsuo
267 series
Sumida
CD75/105 series
Nihon
Coiltronics
CTX series
Sprague
595D/293D series
EC10QS02L (Schottky)
Surface Mount
EC11FS1 (high-speed silicon)
Coilcraft
DT/D03316 series
AVX
TPS series
Sumida
RCH895 series
Sanyo
Miniature Through-Hole
Low-Cost Through-Hole
Motorola
1N5817, 1N5818, (Schottky)
MUR105 (high-speed silicon)
OS-CON series (very low ESR)
Renco
RL1284 series
Nichicon
PL series
SUPPLIER
AVX
PHONE
FAX
USA:
USA:
USA:
USA:
(803) 448-9411
(708) 639-6400
(407) 241-7876
(714) 969-2491
(803) 448-1943
(708) 639-1469
(407) 241-9339
Coilcraft
Coiltronics
(714) 960-6492
81-6-337-6456
Matsuo
Japan: 81-6-337-6450
Motorola
Nichicon
USA:
(800) 521-6274
(602) 952-4190
(708) 843-2798
81-7-5256-4158
USA:
(708) 843-7500
Japan: 81-7-5231-8461
USA: (805) 867-2555
(805) 867-2556
81-3-3494-7414
Nihon
Japan: 81-3-3494-7411
Renco
USA:
(516) 586-5566
(516) 586-5562
(619) 661-1055
81-7-2070-1174
USA:
(619) 661-6835
Sanyo OS-CON
Sprague Electric Co.
Sumida
Japan: 81-7-2070-1005
USA:
USA:
(603) 224-1961
(708) 956-0666
(603) 224-1430
(708) 956-0702
81-3-3607-5144
Japan: 81-3-3607-5111
______________________________________________________________________________________ 11
-5 V/-1 2 V/-1 5 V o r Ad ju s t a b le ,
Hig h -Effic ie n c y, Lo w I DC-DC In ve rt e rs
Q
_Ord e rin g In fo rm a t io n (c o n t in u e d )
___________________Ch ip To p o g ra p h y
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
8 SO
LX
MAX766CPA
MAX766CSA
MAX766C/D
MAX766EPA
MAX766ESA
MAX766MJA
0°C to +70°C
0°C to +70°C
Dice*
OUT
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
8 SO
8 CERDIP**
* Dice are tested at T = +25°C, DC parameters only.
A
**Contact factory for availability and processing to MIL-STD-883.
0. 145"
(3683µm)
V+
FB
V+
SHDN
REF
45/MAX76
GND
0. 080"
(2032µm)
TRANSISTOR COUNT: 443
SUBSTRATE CONNECTED TO V+
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 __________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 (4 0 8 ) 7 3 7 -7 6 0 0
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
相关型号：
MAX766
8-Channel.Multi-Range.5V.12-Bit DAS with 8+4 Bus Interface and Fault Protection[MAX199]
MAXIM
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