For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
General Description
The MAX774/MAX775/MAX776 inverting switching
regulators deliver high efficiency over three decades of
load current. A unique current-limited, pulse-
frequency modulated (PFM) control scheme provides
the benefits of pulse-width modulation (high efficiency
with heavy loads), while using less than 100µA of supply
current (vs. 2mA to 10mA for PWM converters). The result
is high efficiency over a wide range of loads.
These ICs also use tiny external components; their high
switching frequency (up to 300kHz) allows for less than
5mm diameter surface-mount magnetics.
The MAX774/MAX775/MAX776 accept input voltages from
3V to 16.5V, and have preset output voltages of
-5V, -12V, and -15V, respectively. Or, the output voltage
can be user-adjusted with two resistors. Maximum
VIN - VOUT differential voltage is limited only by the break-
down voltage of the chosen external switch transistor.
These inverters use external P-channel MOSFET switches,
allowing them to power loads up to 5W. If less power is
required, use the MAX764/MAX765/MAX766 inverting
switching regulators with on-board MOSFETs.
Applications
LCD-Bias Generators
High-Efficiency DC-to-DC Converters
Battery-Powered Applications
Data Communicators
Features
♦85% Efficiency for 5mA to 1A Load Currents
♦Up to 5W Output Power
♦100µA (max) Supply Current
♦5µA (max) Shutdown Current
♦3V to 16.5V Input Range
♦-5V (MAX774), -12V (MAX775), -15V (MAX776),
or Adjustable Output Voltage
♦Current-Limited PFM Control Scheme
♦300kHz Switching Frequency
Ordering Information
*Contact factory for dice specifications.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
________________________________________________________________ Maxim Integrated Products 1
1
2
3
45
8
7
6
MAX774
MAX775
MAX776
DIP/SO
TOP VIEW
GND
EXT
CS
V+
OUT
FB
SHDN
REF
Pin Configuration
MAX774
OUTPUT
-5V
REF
SHDN
GND
V+
CS
EXT
OUT
ON/OFF
INPUT
3V TO 16V
P
FB
Typical Operating Circuit
PART TEMP RANGE PIN-PACKAGE
MAX774CPA 0°C to +70°C 8 Plastic DIP
MAX774CSA 0°C to +70°C 8 SO
MAX774C/D 0°C to +70°C Dice*
MAX774EPA -40°C to +85°C 8 Plastic DIP
MAX774ESA -40°C to +85°C 8 SO
MAX774MJA -55°C to +125°C 8 CERDIP
19-0191; Rev 2; 12/02
EVALUATION KIT
AVAILABLE
Ordering Information continued on last page.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Supply Voltages
V+ to OUT ...........................................................................21V
V+ to GND ..............................................................-0.3V, +17V
OUT to GND ........................................................-0.3V, to -17V
REF, SHDN, FB, CS...................................-0.3V to (V+ + 0.3V)
EXT ...............................................(VOUT - 0.3V) to (V+ + 0.3V)
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:
MAX77_C__ .........................................................0°C to +70°C
MAX77_E__ ......................................................-40°C to +85°C
MAX77_MJA ...................................................-55°C to +125°C
Maximum Junction Temperatures:
MAX77_C__/E_ _ ...........................................................+150°C
MAX77_MJA..................................................................+175°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
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.
PARAMETER SYMBOL CONDITIONS
Output Voltage Line Regulation
(Circuit of Figure 2—
Bootstrapped)
MIN TYP MAX UNITS
V+ Input Voltage Range V+ 3.0 16.5 V
Supply Current
V+ = 16.5V, SHDN ≤0.4V (operating)
MAX774, 4V ≤V+ ≤15V, ILOAD = 0.5A
100
µA
0.035
mV/V
V+ = 10V, SHDN ≥1.6V (shutdown) 25
MAX776, 4V ≤V+ ≤6V, ILOAD = 0.1A 0.137
V+ = 16.5V, SHDN ≥1.6V (shutdown) 4
FB Trip Point 3V ≤V+ ≤16.5V -10 10 mV
FB Input Current IFB
MAX77_C
MAX775, 4V ≤V+ ≤8V, ILOAD = 0.2A
±50
nA
0.088
MAX77_E ±70
MAX775, 0mA ≤ILOAD ≤500mA, V+ = 5V 1.5
MAX77_M ±90
Output Voltage Load Regulation
(Circuit of Figure 2—
Bootstrapped)
Output Voltage VOUT
MAX774 -4.80 -5 -5.20
V
MAX774, 0A ≤ILOAD ≤1A, V+ = 5V 1.5
MAX775
mV/A
-11.52 -12 -12.48
MAX776, 0mA ≤ILOAD ≤400mA, V+ = 5V
MAX776
1.0
-14.40 -15 -15.60
Reference Voltage VREF IREF = 0µA
MAX77_C 1.4700 1.5 1.5300
V
MAX77_E 1.4625 1.5 1.5375
MAX77_M 1.4550 1.5 1.5450
REF Load Regulation 0µA ≤IREF ≤100µA MAX77_C/E 410 mV
MAX77_M 415
REF Line Regulation 3V ≤V+ ≤16.5V 40 100 µV/V
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
3V ≤V+ ≤16.5V
V+ = 16.5V, SHDN = 0V or V+
MAX774, V+ = 5V, ILOAD = 1A
MAX776, V+ = 5V, ILOAD = 400mA
MAX775, V+ = 5V, ILOAD = 500mA
CONDITIONS
V1.6 VIH
SHDN Input Voltage High
µA±1SHDN Input Current
%
82
Efficiency
(Circuit of Figure 2—
Bootstrapped) 87
CEXT = 1nF, V+ = 12V
CEXT = 1nF, V+ = 12V
ns50
V+ = 12V
V+ = 12V
EXT Fall Time
µs
88
ns
1.8 2.3 2.8tOFF (max)Switch Minimum Off-Time
µs12 16 20 tON (max)Switch Maximum On-Time
µA±1CS Input Current
50
UNITS
MIN TYP MAX
SYMBOL
EXT Rise Time
PARAMETER
160 210 260
3V ≤V+ ≤16.5V mV
180 210 240
VCS
Current-Limit Trip Level
(V+ – CS)
0.3
3V ≤V+ ≤16.5V V
0.4
VIL
SHDN Input Voltage Low
MAX77_M
MAX77_C/E
MAX77_M
MAX77_C/E
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
4 _______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
90
1 10 1000
MAX774
EFFICIENCY vs. LOAD CURRENT
VOUT = -5V (BOOTSTRAPPED)
70
80
MAX1774/5/6-01a
LOAD CURRENT (mA)
EFFICIENCY (%)
60
50
100
VIN = 5V
VIN = 3V
VIN = 15V
90
50
1 100
MAX774
EFFICIENCY vs. LOAD CURRENT
VOUT = -5V (NONBOOTSTRAPPED)
60
80
MA774/5/6--1b
LOAD CURRENT (mA)
EFFICIENCY (%)
10 1000
70 VIN = 15V
VIN = 5V
VIN = 4V
90
50
-40 -20 40 100
MAX774
EFFICIENCY vs. TEMPERATURE
60
80
MAX774/5/6-2
TEMPERATURE (°C)
EFFICIENCY (%)
2006080
70
ILOAD = 600mA
ILOAD = 1A
ILOAD = 100mA
VIN = 5V
BOOTSTRAPPED
90
50
1 100
MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -15V (BOOTSTRAPPED)
60
80
MA774/5/6-1c
LOAD CURRENT (mA)
EFFICIENCY (%)
10 1000
70
VIN = 4V
VIN = 3V
VIN = 6V
VIN = 5V
90
50
1 100
MAX774/MAX775/MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -24V (NONBOOTSTRAPPED)
60
80
MA774/5/6--1f
LOAD CURRENT (mA)
EFFICIENCY (%)
10 1000
70
VIN = 4V
VIN = 5V
VIN = 6V
90
50
1 100
MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -15V (NONBOOTSTRAPPED)
60
80
MA774/5/6-1d
LOAD CURRENT (mA)
EFFICIENCY (%)
10 1000
70 VIN = 4V
VIN = 5V
VIN = 15V VIN = 6V
90
50
1 100
MAX775
EFFICIENCY vs. OUTPUT CURRENT
VOUT = -12V (BOOTSTRAPPED)
60
80
MA774/5/6--1e
OUTPUT CURRENT (mA)
EFFICIENCY (%)
10 1000
70
VIN = 4V
VIN = 5V
VIN = 8V
90
50
1 100
MAX774/MAX775/MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -24V OUTPUT (ZENER CONNECTION)
60
80
MA774/5/6--1g
LOAD CURRENT (mA)
EFFICIENCY (%)
10 1000
70
VIN = 4V
VIN = 5V
VIN = 6V
88
74
2 4 10 16
MAX774
EFFICIENCY vs. INPUT VOLTAGE
VOUT = -5V AT 100mA
78
76
84
86
MAX774/5/6-3
INPUT VOLTAGE (V)
EFFICIENCY (%)
861214
82
80
BOOTSTRAPPED
NONBOOTSTRAPPED
VOUT = -5V AT 100mA
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
_______________________________________________________________________________________ 5
_____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
2.5
1.5
-60 60
SWITCH OFF-TIME vs. TEMPERATURE
2.0
MAX761-13
TEMPERATURE (°C)
tOFF (µs)
0 120
V+ = 5V
5.0
2.5
100
STARTUP VOLTAGE
vs. LOAD CURRENT (BOOTSTRAPPED)
3.0
4.5
MA744/5/6-14
LOAD CURRENT (mA)
START-UP VOLTAGE (V)
10 1000
3.5
1
4.0 VOUT = -12V
VOUT = -15V
VOUT = -5V
5.0
2.5
0.1 100
STARTUP VOLTAGE
vs. LOAD CURRENT (NONBOOTSTRAPPED)
3.0
4.5
MA744/5/6-15
LOAD CURRENT (mA)
START-UP VOLTAGE (V)
10 1000
3.5
1
4.0 VOUT = -24V
VOUT = -15V
VOUT = -12V
VOUT = -5V
2200
800
2 4 10 16
MAX774
MAXIMUM LOAD vs. INPUT VOLTAGE
1200
1000
1800
2000
MAX774/5/6-16
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
861214
1600
1400
BOOTSTRAPPED
NONBOOTSTRAPPED
VOUT = -5V
20
-60 -40 60 140
EXT RISE AND FALL TIMES
vs. TEMPERATURE
40
30
MAX774/5/6-9
TEMPERATURE (°C)
tRISE & tFALL (ns)
40200-20 80 120100
50
5V RISE
60
80
70
90
100
120
110
130
5V FALL
12V RISE
12V FALL
CEXT = 1nF
-60 -40 60 140
EXT RISE AND FALL TIMES
vs. TEMPERATURE
MAX774/5/6-10
TEMPERATURE (°C)
tRISE & tFALL (ns)
40200-20 80 120100
5V RISE
450
400
500
5V FALL
12V RISE
12V FALL
CEXT = 5nF
300
250
350
150
100
200
50
17
15
-60 60
SWITCH ON-TIME vs. TEMPERATURE
16
MAX761-13
TEMPERATURE (°C)
ton (µs)
0 120
V+ = 5V
8.0
7.8
7.6
7.4
7.2
7.0
6.8
6.6
6.4
6.2
6.0
-60 -40 60 140
SWITCH ON-TIME/OFF-TIME RATIO
MAX774/5/6-6
TEMPERATURE (°C)
tON/tOFF RATIO (µs/µs)
40200-20 80 120100
V+ = 5V
4.0
0
-60 -40 60 140
SHUTDOWN CURRENT
vs. TEMPERATURE
1.0
0.5
2.5
3.5
MAX774/5/6-7
TEMPERATURE (°C)
ICC (µA)
40200-20 80 120100
2.0
1.5
3.0
V+ = 15V
V+ = 8V
V+ = 4V
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
6 _______________________________________________________________________________________
80
66
-60 -40 60 140
OPERATING SUPPLY CURRENT
vs. TEMPERATURE
70
68
76
78
MAX774/5/6-8
TEMPERATURE (°C)
ICC (µA)
40200-20 80 120100
74
72
V+ = 16.5V
V+ = 10V
V+ = 3V
1.506
1.492
-60 -40 60 140
REFERENCE
TEMPERATURE COEFFICIENT
1.496
1.494
1.502
1.504
MAX774/5/6-12
TEMPERATURE (°C)
REFERENCE OUTPUT (V)
40200-20 80 120100
1.500
1.498
235
230
225
220
215
210
205
200
195
190
185
-60 -40 60 140
CS TRIP LEVEL
MAX774/5/6-11
TEMPERATURE (°C)
CS TRIP LEVEL (mV)
40200-20 80 120100
250
200
150
100
50
0
-60 -40 60 140
REFERENCE
OUTPUT RESISTANCE
MAX774/5/6-13
TEMPERATURE (°C)
REFERENCE OUTPUT RESISTANCE (Ω)
40200-20 80 120100
IREF = 50µA
IREF = 100µA
IREF = 10µA
_____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
_______________________________________________________________________________________ 7
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
CIRCUIT OF FIGURE 2
V+ = 6.5V, ILOAD = 1A, VOUT = -5V
A: OUTPUT RIPPLE, 200mV/div
B: EXT WAVEFORM, 10V/div
C: INDUCTOR CURRENT, 2A/div
OPERATING WAVEFORMS
10µs/div
A
B
C
CIRCUIT OF FIGURE 2
VOUT = -5V, V+ = 4.7V
ILOAD = 1.05A (1A/div)
INDUCTOR CURRENT NEAR FULL LOAD
20µs/div
1A/div
0A
CIRCUIT OF FIGURE 2
ILOAD = 300mA, VOUT = -5V
V+ = 8V, L = 22µH
CONTINUOUS CONDUCTION
AT ONE-HALF CURRENT LIMIT
20µs/div
1A/div
0A
CIRCUIT OF FIGURE 2
V+ = 6V, ILOAD = 1A, VOUT = -5V
A: SHUTDOWN PULSE, 0V TO V+, 5V/div
B: VOUT, 2V/div
ENTRY/EXIT FROM SHUTDOWN
2ms/div
A
B
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
8 _______________________________________________________________________________________
______________________________________________________________Pin Description
PIN NAME FUNCTION
1OUT
2FB
3SHDN
4REF 1.5V reference output that can source 100µA. Bypass to ground with 0.1µF.
5V+ Positive power-supply input
6CS Noninverting input to the current-sense comparator. Typical trip level is 210mV (relative to V+).
7EXT The gate-drive output for an external P-channel power MOSFET. EXT swings from OUT to V+.
8GND Ground
The sense input for fixed-output operation (VFB = VREF). OUT is connected to the internal voltage divider,
and it is the negative supply input for the EXT driver.
Feedback input. When VFB = VREF, the output will be the factory preset value. For adjustable operation,
use an external voltage divider, as described in the Adjustable Output section.
Active-high shutdown input. With SHDN high, the part is in shutdown mode and the supply current is less
than 5µA. Connect to GND for normal operation.
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
CIRCUIT OF FIGURE 2
V+ = 6V, VOUT = -5V
A: ILOAD, 30mA TO 1A, 1A/div
B: VOUT, 100mV/div, AC-COUPLED
LOAD-TRANSIENT RESPONSE
100µs/div
A
B
CIRCUIT OF FIGURE 2
VOUT = -5V, ILOAD = 1A
A: V+, 3V TO 8V, 5V/div
B: VOUT, 100mV/div, AC-COUPLED
LINE-TRANSIENT RESPONSE
2ms/div
A
B
Detailed Description
The MAX774/MAX775/MAX776 are negative-output,
inverting power controllers that can be configured to drive
an external P-channel MOSFET. The output voltages are
preset to -5V (MAX774), -12V (MAX775), or -15V
(MAX776). Additionally, all three parts can be set to any
desired output voltage using an external resistor divider.
The MAX774/MAX775/MAX776 have a unique control
scheme (Figure 1) that combines the advantage of
pulse-skipping, pulse-frequency-modulation (PFM)
converters (ultra-low supply current) with the advan-
tage of pulse-width modulation (PWM) converters (high
efficiency with heavy loads). This control scheme
allows the devices to achieve 85% efficiency with loads
from 5mA to 1A.
As with traditional PFM converters, the external
P-channel MOSFET power transistor is turned on when
the voltage comparator senses that the output is below
the reference voltage. However, unlike traditional PFM
converters, switching is controlled by the combination
of a switch current limit (210mV/RSENSE) and
on-time/off-time limits set by one-shots. Once turned
on, the MOSFET stays on until the 16µs maximum on-
time limit is reached or the switch current reaches its
limit (as set by the current-sense resistor).
Once off, the switch is typically held off for a minimum of
2.3µs. It will stay off until the output drops below the level
determined by VREF and the feedback divider network.
With light loads, the MOSFET switches on for one or
more cycles and then switches off, much like in tradi-
tional PFM converters. To increase light-load efficiency,
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
_______________________________________________________________________________________ 9
N
1.5V
REFERENCE
Q TRIG
ONE-SHOT
QTRIG
ONE-SHOT
CURRENT-
CONTROL CIRCUITS
MODE
COMPARATOR
ERROR
COMPARATOR
CURRENT
COMPARATOR
FROM V+
FROM OUT
0.2V
(FULL CURRENT)
0.1V
(HALF CURRENT)
FROM
V+
MAX774
MAX775
MAX776
REF
V+
SHDN
FB
OUT
CS
EXT
GND
S
R
Q
50mV
Figure 1. Functional Diagram
MAX774/MAX775/MAX776
the current limit for the first two pulses is set to one-half
the peak current limit. If those pulses bring the output
voltage into regulation, the voltage comparator keeps
the MOSFET off, and the current limit remains at one-half
the peak current limit. If the output voltage is out of
regulation after two consecutive pulses, the current limit
for the next pulse will equal the full current limit.
With heavy loads, the MOSFET first switches twice at
one-half the peak current value. Subsequently, it stays
on until the switch current reaches the full current limit,
and then turns off. After it is off for 2.3µs, the MOSFET
switches on once more, and remains on until the switch
current again reaches its limit. This cycle repeats until
the output is in regulation.
A benefit of this control scheme is that it is highly effi-
cient over a wide range of input/output ratios and load
currents. Additionally, PFM converters do not operate
with constant-frequency switching, and have relaxed
stability criterion (unlike PWM converters). As a result,
their external components require smaller values.
With PFM converters, the output voltage ripple is not
concentrated at the oscillator frequency (as it is with
PWM converters). For applications where the ripple fre-
quency is important, the PWM control scheme must be
used. However, for many other applications, the smaller
capacitors and lower supply current of the PFM control
scheme make it the better choice. The output voltage
ripple with the MAX774/MAX775/MAX776 can be held
quite low. For example, using the circuit of Figure 2,
only 100mV of output ripple is produced when generat-
ing a -5V at 1A output from a +5V input.
Bootstrapped vs.
Nonbootstrapped Operation
Figures 2 and 3 are the standard application circuits
for bootstrapped mode, and Figure 4 is the circuit for
nonbootstrapped mode. Since EXT is powered by OUT,
using bootstrapped or nonbootstrapped mode will
directly affect the gate drive to the FET. EXT swings
from V+ to VOUT. In bootstrapped operation, OUT is
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
10 ______________________________________________________________________________________
MAX774
MAX775
MAX776
OUT V+
SHDN CS
FB EXT
GND
P
7
8
C2
0.1µFR1
0.07Ω
C1
150µF
6
5
2
3
1
REF
4
Q1
Si9435
1N5822/
MBR340
L1
22µH
C4*
VIN
C3
0.1µF
VOUT
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
PRODUCT
MAX774
MAX775
MAX776
OUTPUT
VOLTAGE (V)
-5
-12
-15
INPUT
VOLTAGE (V)
3 to 15
3 to 8
3 to 5
OUTPUT
CURRENT (A)
1
0.5
0.4
NOTE: Si9435 HAS VGS OF 20V MAX
MAX774
MAX775
MAX776
OUT V+
SHDN
CS
FB
EXT
GND
P
7
8
R2 R3
0.07Ω
C1
150µF
6
5
2
3
1
REF
4
Q1
Si9435
1N5822/
MBR340
L1
22µHC4*
VIN
C3
0.1µF
VOUT
C2
0.1µF
R1
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
Figure 2. Bootstrapped Connection Using Fixed Output
Voltages
Figure 3. Bootstrapped Connection Using External Feedback
Resistors
Figure 4. Nonbootstrapped Operation (VIN > 4.5V)
MAX774
MAX775
MAX776
OUT V+
SHDN
CS
FB
EXT
GND
P
7
8
R2 R3
0.07Ω
C1
150µF
6
5
2
3
1
REF
4
Q1
Si9435
1N5822/
MBR340
L1
22µH
C4*
VIN
C3
0.1µF
VOUT
C2
0.1µF
R1
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
connected to the output voltage (-5V, -12V, -15V). In
nonbootstrapped operation, OUT is connected to
ground, and EXT now swings from V+ to ground.
At high input-to-output differentials, it may be neces-
sary to use nonbootstrapped mode to avoid the 21V V+
to VOUT maximum rating. Also, observe the VGS maxi-
mum rating of the external transistor. At intermediate
voltages and currents, the advantages of bootstrapped
vs. nonbootstrapped operation are slight. When input
voltages are less than about 4V, always use the boot-
strapped circuit.
Shutdown and Quiescent Current
The MAX774/MAX775/MAX776 are designed to save
power in battery-powered applications. A TTL/CMOS
logic-level shutdown input (SHDN) has been provided
for the lowest-power applications. When shut down
(SHDN = V+), most internal bias current sources and
the reference are turned off so that less than 5µA of
current is drawn.
In normal operation, the quiescent current will be less
than 100µA. However, this current is measured by forc-
ing the external switch transistor off. Even with no load,
in an actual application, additional current will be
drawn to supply the feedback resistors’ and the diode’s
and capacitor’s leakage current. Under no-load condi-
tions, you should see a short current pulse at half the
peak current approximately every 100ms (the exact
period depends on actual circuit leakages).
EXT Drive Voltages
EXT swings from OUT to V+ and provides the drive out-
put for an external power MOSFET. When using the on-
chip feedback resistors for the preset output voltages,
the voltage at OUT equals the output voltage. When
using external feedback resistors, OUT may be tied to
GND or some other potential between VOUT and GND.
Always observe the V+ to OUT absolute maximum rat-
ing of 21V. For V+ to output differentials greater than
21V, OUT must be tied to a potential more positive than
the output and, therefore, the output voltage must be
set with an external resistor divider.
In nonbootstrapped operation with low input voltages
(<4V), tie OUT to a negative voltage to fully enhance the
external MOSFET. Accomplish this by creating an inter-
mediate voltage for VOUT with a zener diode (Figure 5).
__________________Design Procedure
Setting the Output Voltage
The MAX774/MAX775/MAX776 are preset for -5V, -12V,
and -15V output voltages, respectively; however, they
may also be adjusted to other values with an external
voltage divider. For the preset output voltage, connect
FB to REF and connect OUT to the output (Figure 3). In
this case, the output voltage is sensed by OUT.
For an adjustable output (Figures 3 and 4), connect an
external resistor divider from the output voltage to FB,
and from FB to REF. In this case, the divided-down out-
put voltage is sensed via the FB pin.
There are three reasons to use the external resistor divider:
1) An output voltage other than a preset value is
desired.
2) The input-to-output differential exceeds 21V.
3) The output voltage (VOUT to GND) exceeds -15V.
See Figures 3 and 4 for adjustable operation. The
impedance of the feedback network should be low
enough that the input bias current of FB is not a factor.
For best efficiency and precision, allow 10µA to flow
through the network. Calculate (VREF -V
FB) / R1 =
10µA. Since VREF = 1.5V and VFB = 0V, R1 becomes
150kΩ. Then calculate R2 as follows:
R2 VOUT
___ =_______
R1 VREF
(or, VOUT = 10µA)
______
R2
Choosing an Inductor
Practical inductor values range from 10µH to 50µH.
The maximum inductor value is not particularly critical.
For highest current at high VOUTto V+ ratios, the
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
______________________________________________________________________________________ 11
Figure 5. Connection Using Zener Diode to Boost Base Drive
R1
MAX774
MAX775
MAX776
OUT GND
FB
R2
8
2
1
REF
4
0.1µF
0.1µFVOUT
RZ
6V ≤ VZ + VIN ≤ 10V
VOUT – VZ > IZ
RZ
IZ = ZENER BREAKDOWN CURRENT
VZ = ZENER BREAKDOWN VOLTAGE
VIN = INPUT SUPPLY VOLTAGE
MAX774/MAX775/MAX776
inductor should not be so large that the peak current
never reaches the current limit. That is:
[V+(min) - VSW(max)]x 12µs
L(max) ≤_______________________________
ILIM(max)
This is only important if
VIN 1t
OFF(min)
_______< — = ___________
VOUT 6t
ON(max)
More important is that the inductor not be so small that
the current rises much faster than the current-limit
comparator can respond. This would be wasteful and
reduce efficiency. Calculate the minimum inductor value
as follows:
[V+(max) - VSW(min)]x 0.3µs
L(min) ≥_______________________________
δ(I) x ILIM(min)
Where L is in µH, 0.3µs is an ample time for the com-
parator response, ILIM is the current limit (see the
Current-Sense Resistor section), and δ(I) is the allow-
able percentage of overshoot. As an example, Figure
2's circuit uses a 3A peak current. If we allow a 15%
overshoot and 15V is the maximum input voltage, then
L(min) is 16µH. The actual value of L above this limit
has minimal effect on this circuit's operation.
For highest efficiency, use a coil with low DC resistance.
Coils with 30mΩor lower resistance are available. To min-
imize radiated noise, use a torroid, pot-core, or shielded-
bobbin inductor. Inductors with a ferrite core or equivalent
are recommended. Make sure that the inductor’s satura-
tion current rating is greater than ILIM(max).
Diode Selection
The ICs’ high switching frequencies demand a high-
speed rectifier. Schottky diodes such as the 1N5817 to
1N5822 families are recommended. Choose a diode
with an average current rating approximately equal to
or greater than ILIM (max) and a voltage rating higher
than VIN(max) + VOUT. For high-temperature applica-
tions, Schottky diodes may be inadequate due to their
high leakage currents; instead, high-speed silicon
diodes may be used. At heavy loads and high tempera-
ture, the benefits of a Schottky diode’s low forward volt-
age may outweigh the disadvantages of its high leak-
age current.
Current-Sense Resistor
The current-sense resistor limits the peak switch cur-
rent to 210mV/RSENSE, where RSENSE is the value of
the current-sense resistor, and 210mV is the current-
sense comparator threshold (see Current-Limit Trip
Level in the Electrical Characteristics).
To maximize efficiency and reduce the size and cost of
external components, minimize the peak current.
However, since the output current is a function of the
peak current, do not set the limit too low. See Figures
6–9 to determine the sense resistor, as well as the peak
current, for the required load current.
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
12 ______________________________________________________________________________________
MAXIMUM OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
0
500
1000
1500
2000
2500
34 567 8 910111213 14 15
VOUT = -5V
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.08Ω
RSENSE = 0.09Ω
RSENSE = 0.07Ω
MAX775-fig6
Figure 6. MAX774 Maximum Output Current vs. Input Voltage
(VOUT = -5V)
Figure 7. MAX775 Maximum Output Current vs. Input Voltage
(VOUT = -12V)
MAXIMUM OUTPUT CURRENT (mA)
0
200
400
600
800
1000
9
INPUT VOLTAGE (V)
MAX775-FIG07
34 56 78
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
RSENSE = 0.08Ω
RSENSE = 0.09Ω
VOUT = -12V
To choose the proper current-sense resistor, simply fol-
low the two-step procedure outlined below:
1) Determine:
• Input voltage range, V+
• Maximum (absolute) output voltage, VOUT
• Maximum output current, ILOAD
For example, let V+ range from 4V to 6V, and
choose VOUT = -24V and IOUT = 150mA.
2) Next, referring to Figure 9, find the curve with the
lowest current limit whose output current (with the
lowest input voltage) meets your requirements.
In our example, a curve where IOUT is >150mA with a
4V input and a -24V output is optimal.
The RSENSE = 80mΩ(Figure 9) shows only approxi-
mately 125mA of output current with a 4V input, so we
look next at the RSENSE = 70mΩline. It shows IOUT
>150mA for V+ = 4V and VOUT = -24V. The current limit
will be 0.210V / 0.070Ω= 3A. These curves take into
account worst-case inductor (±10%) and current-
sense trip levels, but not sense-resistor tolerance. The
switch on resistance is 70mΩ.
Standard wire-wound and metal-film resistors have
an inductance high enough to degrade performance.
Metal-film resistors are usually deposited on a ceramic
rod in a spiral, making their inductances relatively high.
Surface-mount (or chip) resistors have very little induc-
tance and are well suited for use as current-sense
resistors. To use through-hole resistors, IRC has a wire
resistor that is simply a band of metal shaped as a “U”
so that inductance is less than 10nH (an order of mag-
nitude less than metal-film resistors). These are avail-
able in resistance values between 5mΩand 0.1Ω.
External Switching Transistor
The MAX774/MAX775/MAX776 are capable of driving
P-channel enhancement-mode MOSFET transistors only.
The choice of power transistor is dictated by input and
output voltage, peak current rating, on-resistance, gate-
source threshold, and gate capacitance. The drain-to-
source rating must be greater than the V+ - VOUT
input-to-output voltage differential. The gate-to-source
rating must be greater than V+ (the source voltage) plus
the absolute value of the most negative swing of EXT.
For bootstrapped operation, the most negative swing of
EXT is VOUT. In nonbootstrapped operation, this may be
ground or some other negative voltage. Gate capaci-
tance is not normally a limiting factor, but values should
be less than 1nF for best efficiency. For maximum effi-
ciency, the MOSFET should have a very-low on-resis-
tance at the peak current and be capable of handling
that current. The transistor chosen for the typical operat-
ing circuit has a 30V drain-source voltage limit and a
0.07Ωdrain-source on-resistance at VGS = -10V.
Table 1 lists suppliers of switching transistors suitable
for use with the MAX774/MAX775/MAX776.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
______________________________________________________________________________________ 13
Figure 8. MAX776 Maximum Output Current vs. Input Voltage
(VOUT = -15V)
Figure 9. MAX774/MAX775/MAX776 Maximum Output Current
vs. Input Voltage (VOUT = -24V)
MAXIMUM OUTPUT CURRENT (mA)
100
INPUT VOLTAGE (V)
MAX776-FIG08
200
300
400
500
600
700
34567
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
RSENSE = 0.08Ω
RSENSE = 0.09Ω
VOUT = -15V
MAXIMUM OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
0
34 5678 910111213 14 15
MAX776-FIG09
200
400
600
800
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
RSENSE = 0.08Ω
RSENSE = 0.09Ω
VOUT = -24V
Capacitors
Choose the output capacitor (C4 of Figures 2, 3, and 4)
to be consistent with size, ripple, and output voltage
requirements. Place capacitors in parallel if the size
desired is unobtainable. This will not only increase the
capacitance, but also decrease the capacitor’s ESR (a
major contributor of ripple). A 330µF tantalum output filter
capacitor with 0.07ΩESR typically maintains 120mVP-P
output ripple when generating -5V at 1A from a 5V
input. Smaller capacitors are acceptable for lighter
loads or in applications that can tolerate higher output
ripple.
The value of C4 is chosen such that it acquires as
small a charge as possible during the switch on-time.
The amount of ripple as a function of capacitance is
give by:
VOUT x IOUT x ESR IOUT x tOFF(min)
∆VP-P =_____________________ +_________________
VIN C
When evaluating this equation, be sure to use the
capacitance value at the switching frequency. At
200kHz, the 330µF tantalum capacitor of Figures 2, 3,
or 4 may degrade by a factor of ten, which will signifi-
cantly alter the ripple voltage calculation.
The ESR of both the bypass and filter capacitors also
affects efficiency. Best performance is obtained by
doubling up on the filter capacitors or using low-ESR
capacitors. Capacitors must have a ripple current rat-
ing equal to the peak current.
The smallest low-ESR SMT capacitors currently avail-
able are the Sprague 595D series. Sanyo OS-CON
organic semiconductor through-hole capacitors also
exhibit low ESR and are especially effective at low tem-
peratures. Table 1 lists the phone numbers of these
and other manufacturers.
PC Layout and Grounding
Due to high current levels and fast switching wave-
forms, proper PC board layout is essential. Use a star
ground configuration; connect the ground lead of the
input bypass capacitor, the output capacitor, the induc-
tor, and the GND pin of the MAX774/MAX775/MAX776
at a common point very close to the device. Addi-
tionally, input capacitor C2 (Figures 3 and 4) should be
placed extremely close to the device.
If an external resistor divider is used (Figures 3 and 4),
the trace from FB to the resistors must be extremely short.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
14 ______________________________________________________________________________________
Table 1. Component Suppliers
SUPPLIER PHONE FAX
Coiltronics (407) 241-7876 (407) 241-9339
Gowanda (716) 532-2234 (716) 532-2702
Sumida Japan 81-3-3607-5111 81-3-3607-5144
Sumida USA (708) 956-0666 (708) 956-0702
Kemet (803) 963-6300 (803) 963-6322
Matsuo (714) 969-2491 (714) 960-6492
Nichicon (708) 843-7500 (708) 843-2798
Sanyo Japan 81-7-2070-6306 81-7-2070-1174
Sanyo USA (619) 661-6835 (619) 661-1055
Sprague (603) 224-1961 (603) 224-1430
United Chemi-Con (714) 255-9500 (714) 255-9400
Motorola (800) 521-6274 (602) 952-4190
Nihon USA 81-3-3494-7411 81-3-3494-7414
Nihon Japan (805) 867-2555 (805) 867-2556
Harris (407) 724-3729 (407) 724-3937
International Rectifier (310) 322-3331 (310) 322-3332
Siliconix (408) 988-8000 (408) 970-3950
IRC (704) 264-8861 (704) 264-8866
INDUCTORS
CAPACITORS
DIODES
POWER MOSFETS
CURRENT-SENSE RESISTORS
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
______________________________________________________________________________________ 15
Chip TopographyOrdering Information (continued)
.109"
(2.769mm)
0.080
(2.032mm)
GND
OUT
REF
SHDN
FB
V+
CS
EXT
TRANSISTOR COUNT: 442;
SUBSTRATE CONNECTED TO V+.
PART TEMP RANGE PIN-PACKAGE
MAX775CPA 0°C to +70°C 8 Plastic DIP
MAX775CSA 0°C to +70°C 8 SO
MAX775C/D 0°C to +70°C Dice*
MAX775EPA -40°C to +85°C 8 Plastic DIP
MAX775ESA -40°C to +85°C 8 SO
MAX775MJA -55°C to +125°C 8 CERDIP
MAX776CPA 0°C to +70°C 8 Plastic DIP
MAX776CSA 0°C to +70°C 8 SO
MAX776C/D 0°C to +70°C Dice*
MAX776EPA -40°C to +85°C 8 Plastic DIP
MAX776ESA -40°C to +85°C 8 SO
MAX776MJA -55°C to +125°C 8 CERDIP
*Contact factory for dice specifications.
L
DIM
A
A1
B
C
D
E
e
H
h
L
α
MIN
0.053
0.004
0.014
0.007
0.189
0.150
0.228
0.010
0.016
0˚
MAX
0.069
0.010
0.019
0.010
0.197
0.157
0.244
0.020
0.050
8˚
MIN
1.35
0.10
0.35
0.19
4.80
3.80
5.80
0.25
0.40
0˚
MAX
1.75
0.25
0.49
0.25
5.00
4.00
6.20
0.50
1.27
8˚
INCHES MILLIMETERS
α
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
HE
D
e
A
A1 C
h x 45˚
0.127mm
0.004in.
B
1.27 BSC0.050 BSC
21-325A
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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.
16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQInverting DC-to-DC Controllers
C
AA2
E1
D
E
eA
eB
A3
B1
B
DIM
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
MIN
–
0.015
0.125
0.055
0.016
0.050
0.008
0.348
0.005
0.300
0.240
–
0.115
0˚
MAX
0.200
–
0.175
0.080
0.022
0.065
0.012
0.390
0.035
0.325
0.280
0.400
0.150
15˚
MIN
–
0.38
3.18
1.40
0.41
1.27
0.20
8.84
0.13
7.62
6.10
–
2.92
0˚
MAX
5.08
–
4.45
2.03
0.56
1.65
0.30
9.91
0.89
8.26
7.11
10.16
3.81
15˚
INCHES MILLIMETERS
2.54 BSC
7.62 BSC
0.100 BSC
0.300 BSC
A1
L
D1
e
21-324A
α
8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
C
A
D
B1
B
DIM
A
B
B1
B2
C
D
E
E1
e
L
L1
Q
S
S1
α
MIN
–
0.014
0.038
0.023
0.008
–
0.220
0.290
0.125
0.150
0.015
–
0.005
0˚
MAX
0.200
0.023
0.065
0.045
0.015
0.405
0.310
0.320
0.200
–
0.060
0.055
–
15˚
MIN
–
0.36
0.97
0.58
0.20
–
5.59
7.37
3.18
3.81
0.38
–
0.13
0˚
MAX
5.08
0.58
1.65
1.14
0.38
10.29
7.87
8.13
5.08
–
1.52
1.40
–
15˚
INCHES MILLIMETERS
Q
L
S1
e
21-326D
8-PIN CERAMIC
DUAL-IN-LINE
PACKAGE
α
S
L1
E
E1 2.54 BSC0.100 BSC
B2
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
