Maxim MAX776CPA -5v/-12v/-15v or adjustable, high-efficiency, low iq inverting dc-to-dc controller Datasheet

19-0191; Rev 2; 12/02
TION KIT
EVALUA
ABLE
IL
A
AV
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
Features
♦ 85% Efficiency for 5mA to 1A Load Currents
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 breakdown voltage of the chosen external switch transistor.
♦ 300kHz Switching Frequency
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
♦ 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
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX774CPA
PART
0°C to +70°C
8 Plastic DIP
MAX774CSA
MAX774C/D
MAX774EPA
MAX774ESA
MAX774MJA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
High-Efficiency DC-to-DC Converters
*Contact factory for dice specifications.
Battery-Powered Applications
Ordering Information continued on last page.
Data Communicators
Pin Configuration
Typical Operating Circuit
INPUT
3V TO 16V
TOP VIEW
V+
MAX774
ON/OFF
CS
SHDN
EXT
FB
REF
P
OUTPUT
-5V
OUT
1
FB
2
SHDN
3
REF
4
MAX774
MAX775
MAX776
8
GND
7
EXT
6
CS
5
V+
DIP/SO
GND
OUT
________________________________________________________________ Maxim Integrated Products
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.
1
MAX774/MAX775/MAX776
General Description
The MAX774/MAX775/MAX776 inverting switching
regulators deliver high efficiency over three decades of
load current. A unique current-limited, pulsefrequency 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.
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
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
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, ILOAD = 0mA, CREF = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
V+ Input Voltage Range
SYMBOL
CONDITIONS
MIN
V+
TYP
3.0
V+ = 16.5V, SHDN ≤ 0.4V (operating)
Supply Current
FB Input Current
IFB
2
V+ = 16.5V, SHDN ≥ 1.6V (shutdown)
4
-10
Reference Voltage
VREF
5
µA
10
mV
±50
±70
-4.80
-5
-5.20
MAX775
-11.52
-12
-12.48
MAX776
-14.40
-15
-15.60
MAX77_C
1.4700
1.5
1.5300
MAX77_E
1.4625
1.5
1.5375
MAX77_M
1.4550
1.5
1.5450
MAX77_C/E
4
10
MAX77_M
4
15
40
100
IREF = 0µA
REF Line Regulation
3V ≤ V+ ≤ 16.5V
nA
±90
MAX774
0µA ≤ IREF ≤ 100µA
Output Voltage Load Regulation
(Circuit of Figure 2—
Bootstrapped)
V
MAX77_E
REF Load Regulation
Output Voltage Line Regulation
(Circuit of Figure 2—
Bootstrapped)
2
VOUT
16.5
MAX77_C
MAX77_M
Output Voltage
UNITS
100
V+ = 10V, SHDN ≥ 1.6V (shutdown)
3V ≤ V+ ≤ 16.5V
FB Trip Point
MAX
MAX774, 4V ≤ V+ ≤ 15V, ILOAD = 0.5A
0.035
MAX775, 4V ≤ V+ ≤ 8V, ILOAD = 0.2A
0.088
MAX776, 4V ≤ V+ ≤ 6V, ILOAD = 0.1A
0.137
MAX774, 0A ≤ ILOAD ≤ 1A, V+ = 5V
1.5
MAX775, 0mA ≤ ILOAD ≤ 500mA, V+ = 5V
1.5
MAX776, 0mA ≤ ILOAD ≤ 400mA, V+ = 5V
1.0
_______________________________________________________________________________________
V
V
mV
µV/V
mV/V
mV/A
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
MAX774/MAX775/MAX776
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
Efficiency
(Circuit of Figure 2—
Bootstrapped)
MIN
MAX775, V+ = 5V, ILOAD = 500mA
MAX776, V+ = 5V, ILOAD = 400mA
SHDN Input Current
SHDN Input Voltage High
CONDITIONS
MAX774, V+ = 5V, ILOAD = 1A
VIH
V+ = 16.5V, SHDN = 0V or V+
3V ≤ V+ ≤ 16.5V
SHDN Input Voltage Low
VIL
3V ≤ V+ ≤ 16.5V
Current-Limit Trip Level
(V+ – CS)
VCS
3V ≤ V+ ≤ 16.5V
TYP
82
MAX
%
88
87
±1
1.6
MAX77_C/E
MAX77_M
MAX77_C/E
MAX77_M
UNITS
µA
V
180
160
210
210
CS Input Current
0.4
0.3
240
260
V
mV
±1
µA
Switch Maximum On-Time
tON (max)
V+ = 12V
12
16
20
µs
Switch Minimum Off-Time
tOFF (max)
V+ = 12V
1.8
2.3
2.8
µs
EXT Rise Time
EXT Fall Time
CEXT = 1nF, V+ = 12V
CEXT = 1nF, V+ = 12V
50
50
ns
ns
_______________________________________________________________________________________
3
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX774
EFFICIENCY vs. LOAD CURRENT
VOUT = -5V (NONBOOTSTRAPPED)
VIN = 15V
70
ILOAD = 100mA
80
80
EFFICIENCY (%)
VIN = 3V
VIN = 5V
60
VIN = 4V
EFFICIENCY (%)
80
90
MA774/5/6--1b
VIN = 5V
EFFICIENCY (%)
90
MAX1774/5/6-01a
90
MAX774
EFFICIENCY vs. TEMPERATURE
MAX774/5/6-2
MAX774
EFFICIENCY vs. LOAD CURRENT
VOUT = -5V (BOOTSTRAPPED)
VIN = 15V
70
ILOAD = 600mA
ILOAD = 1A
70
60
60
VIN = 5V
BOOTSTRAPPED
1000
100
100
10
-40
1000
0
20
40
60
80
LOAD CURRENT (mA)
TEMPERATURE (°C)
MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -15V (BOOTSTRAPPED)
MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -15V (NONBOOTSTRAPPED)
MAX775
EFFICIENCY vs. OUTPUT CURRENT
VOUT = -12V (BOOTSTRAPPED)
80
VIN = 3V
70
VIN = 15V
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 4V
VIN = 6V
VIN = 4V
70
60
60
10
100
VIN = 8V
VIN = 4V
70
60
50
50
VIN = 5V
80
VIN = 5V
50
1
1000
100
10
1000
1
100
10
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
OUTPUT CURRENT (mA)
MAX774/MAX775/MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -24V (NONBOOTSTRAPPED)
MAX774/MAX775/MAX776
EFFICIENCY vs. LOAD CURRENT
VOUT = -24V OUTPUT (ZENER CONNECTION)
MAX774
EFFICIENCY vs. INPUT VOLTAGE
VOUT = -5V AT 100mA
VIN = 5V
VIN = 6V
88
86
EFFICIENCY (%)
80
VIN = 4V
70
EFFICIENCY (%)
VIN = 5V
80
90
MA774/5/6--1g
VIN = 6V
MA774/5/6--1f
90
VIN = 4V
70
BOOTSTRAPPED
84
82
80
NONBOOTSTRAPPED
78
60
60
100
90
MA774/5/6-1d
90
VIN = 5V
1
-20
LOAD CURRENT (mA)
VIN = 6V
80
1
MA774/5/6--1e
10
MA774/5/6-1c
90
EFFICIENCY (%)
50
50
1
MAX774/5/6-3
50
EFFICIENCY (%)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
76
VOUT = -5V AT 100mA
50
50
1
10
100
LOAD CURRENT (mA)
4
1000
74
1
10
100
LOAD CURRENT (mA)
1000
2
4
6
8
10
12
INPUT VOLTAGE (V)
_______________________________________________________________________________________
14
16
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
4.5
3.5
VOUT = -5V
3.0
4.0
VOUT = -24V
3.5
3.0
2.5
1000
100
10
EXT RISE AND FALL TIMES
vs. TEMPERATURE
EXT RISE AND FALL TIMES
vs. TEMPERATURE
110
80
5V FALL
70
60
12V RISE
50
CEXT = 5nF
4
6
8
10
12
14
16
INPUT VOLTAGE (V)
SWITCH ON-TIME vs. TEMPERATURE
17
V+ = 5V
5V RISE
350
300
250
16
5V FALL
200
12V RISE
150
40
12V FALL
30
100
12V FALL
50
20
-60 -40 -20
0
20
40 60
80 100 120 140
15
-60 -40 -20
0
20
40 60
-60
80 100 120 140
60
0
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
SWITCH OFF-TIME vs. TEMPERATURE
SWITCH ON-TIME/OFF-TIME RATIO
SHUTDOWN CURRENT
vs. TEMPERATURE
7.8
V+ = 5V
3.5
3.0
7.4
7.2
ICC (µA)
tON/tOFF RATIO (µs/µs)
7.6
2.0
4.0
120
MAX774/5/6-7
V+ = 5V
MAX774/5/6-6
8.0
MAX761-13
2.5
tOFF (µs)
2
ton (µs)
90
tRISE & tFALL (ns)
5V RISE
1200
1000
450
400
100
1400
1000
MAX774/5/6-10
LOAD CURRENT (mA)
CEXT = 1nF
120
1
LOAD CURRENT (mA)
500
BOOTSTRAPPED
1600
800
0.1
MAX774/5/6-9
130
100
10
1800
NONBOOTSTRAPPED
VOUT = -5V
2.5
1
tRISE & tFALL (ns)
VOUT = -15V
VOUT = -5V
2000
LOAD CURRENT (mA)
VOUT = -12V
MAX774/5/6-16
VOUT = -12V
START-UP VOLTAGE (V)
START-UP VOLTAGE (V)
4.5
2200
MA744/5/6-15
VOUT = -15V
4.0
5.0
MA744/5/6-14
5.0
MAX774
MAXIMUM LOAD vs. INPUT VOLTAGE
STARTUP VOLTAGE
vs. LOAD CURRENT (NONBOOTSTRAPPED)
MAX761-13
STARTUP VOLTAGE
vs. LOAD CURRENT (BOOTSTRAPPED)
7.0
6.8
2.5
V+ = 15V
2.0
1.5
6.6
V+ = 8V
1.0
6.4
1.5
-60
0
60
TEMPERATURE (°C)
120
6.2
0.5
6.0
0
V+ = 4V
-60 -40 -20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
-60 -40 -20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX774/MAX775/MAX776
_____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
_____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
OPERATING SUPPLY CURRENT
vs. TEMPERATURE
REFERENCE
TEMPERATURE COEFFICIENT
76
1.504
74
72
V+ = 3V
68
1.500
1.498
1.496
1.494
1.492
66
0
20
40 60
80 100 120 140
-60 -40 -20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
CS TRIP LEVEL
REFERENCE
OUTPUT RESISTANCE
MAX774/5/6-11
235
230
225
220
215
210
205
200
195
190
250
REFERENCE OUTPUT RESISTANCE (Ω)
-60 -40 -20
200
IREF = 10µA
150
IREF = 50µA
100
50
IREF = 100µA
0
185
-60 -40 -20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
6
1.502
MAX774/5/6-13
ICC (µA)
V+ = 10V
MAX774/5/6-12
78
REFERENCE OUTPUT (V)
V+ = 16.5V
70
1.506
MAX774/5/6-8
80
CS TRIP LEVEL (mV)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
-60 -40 -20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
_______________________________________________________________________________________
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
INDUCTOR CURRENT NEAR FULL LOAD
OPERATING WAVEFORMS
A
1A/div
B
0A
C
20µs/div
10µs/div
CIRCUIT OF FIGURE 2
VOUT = -5V, V+ = 4.7V
ILOAD = 1.05A (1A/div)
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
CONTINUOUS CONDUCTION
AT ONE-HALF CURRENT LIMIT
ENTRY/EXIT FROM SHUTDOWN
A
1A/div
B
0A
20µs/div
CIRCUIT OF FIGURE 2
ILOAD = 300mA, VOUT = -5V
V+ = 8V, L = 22µH
2ms/div
CIRCUIT OF FIGURE 2
V+ = 6V, ILOAD = 1A, VOUT = -5V
A: SHUTDOWN PULSE, 0V TO V+, 5V/div
B: VOUT, 2V/div
_______________________________________________________________________________________
7
MAX774/MAX775/MAX776
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
A
A
B
B
100µs/div
2ms/div
CIRCUIT OF FIGURE 2
V+ = 6V, VOUT = -5V
A: ILOAD, 30mA TO 1A, 1A/div
B: VOUT, 100mV/div, AC-COUPLED
CIRCUIT OF FIGURE 2
VOUT = -5V, ILOAD = 1A
A: V+, 3V TO 8V, 5V/div
B: VOUT, 100mV/div, AC-COUPLED
______________________________________________________________Pin Description
8
PIN
NAME
FUNCTION
1
OUT
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.
2
FB
3
SHDN
4
REF
1.5V reference output that can source 100µA. Bypass to ground with 0.1µF.
5
V+
Positive power-supply input
6
CS
Noninverting input to the current-sense comparator. Typical trip level is 210mV (relative to V+).
7
EXT
The gate-drive output for an external P-channel power MOSFET. EXT swings from OUT to V+.
8
GND
Ground
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.
_______________________________________________________________________________________
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
MAX774/MAX775/MAX776
V+
FB
MODE
COMPARATOR
REF
MAX774
MAX775
MAX776
50mV
SHDN
ERROR
COMPARATOR
OUT
N
1.5V
REFERENCE
Q
TRIG
ONE-SHOT
FROM V+
S
TRIG
Q
EXT
Q
R
ONE-SHOT
FROM OUT
CURRENT
COMPARATOR
CS
0.1V
(HALF CURRENT)
CURRENTCONTROL CIRCUITS
0.2V
(FULL CURRENT)
FROM
V+
GND
Figure 1. Functional Diagram
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 advantage 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/R SENSE ) and
on-time/off-time limits set by one-shots. Once turned
on, the MOSFET stays on until the 16µs maximum ontime 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 traditional PFM converters. To increase light-load efficiency,
_______________________________________________________________________________________
9
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
VIN
VIN
C1
150µF
C2
0.1µF
1 OUT
3
2
4
V+
1
5
MAX774
SHDN MAX775 CS 6
MAX776
FB
R2
R1
0.07Ω
EXT
Q1
Si9435
P
7
C1
150µF
VOUT
REF
GND
8
C3
0.1µF
1N5822/
MBR340
L1
22µH
C4*
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
OUTPUT
VOLTAGE (V)
INPUT
VOLTAGE (V)
MAX774
-5
3 to 15
1
MAX775
-12
3 to 8
0.5
MAX776
-15
3 to 5
0.4
PRODUCT
NOTE: Si9435 HAS VGS OF 20V MAX
Figure 2. Bootstrapped Connection Using Fixed Output
Voltages
VIN
1 OUT
V+ 5
R3
0.07Ω
C1
150µF
C2
0.1µF
R1
C3
0.1µF
3 SHDN MAX774
2
FB
MAX775 CS 6
MAX776
EXT
4
REF
GND
8
7
L1
22µH
Q1
Si9435
P
VOUT
1N5822/
MBR340
C4*
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
Figure 3. Bootstrapped Connection Using External Feedback
Resistors
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
10
2
V+
5
R3
0.07Ω
SHDN MAX774
FB
MAX775 CS 6
MAX776
7
EXT
R1
4
C3
0.1µF
REF
GND
8
L1
22µH
Q1
Si9435
P
VOUT
1N5822/
MBR340
C4*
* MAX774 = 330µF, 10V
MAX775, MAX776 = 120µF, 20V
Figure 4. Nonbootstrapped Operation (VIN > 4.5V)
OUTPUT
CURRENT (A)
R2
C2
0.1µF
3
OUT
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 efficient 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 frequency 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 generating 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 IQ Inverting DC-to-DC Controllers
VOUT
RZ
1
OUT
GND
8
R2
2
FB
R1
4
MAX774
MAX775
MAX776
REF
0.1µF
6V ≤ VZ + VIN ≤ 10V
VOUT – VZ
> IZ
RZ
IZ = ZENER BREAKDOWN CURRENT
VZ = ZENER BREAKDOWN VOLTAGE
VIN = INPUT SUPPLY VOLTAGE
Figure 5. Connection Using Zener Diode to Boost Base Drive
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 necessary to use nonbootstrapped mode to avoid the 21V V+
to VOUT maximum rating. Also, observe the VGS maximum 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 bootstrapped 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 forcing 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 conditions, 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 output for an external power MOSFET. When using the onchip 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 rating 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 intermediate 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 output 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 (V REF - 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 VOUT  to V+ ratios, the
______________________________________________________________________________________
11
MAX774/MAX775/MAX776
0.1µF
RSENSE = 0.06Ω
2000
1500
1000
RSENSE = 0.07Ω
RSENSE = 0.08Ω
500
0
RSENSE = 0.09Ω
VOUT = -5V
3 4
5 6
1000
VOUT = -12V
800
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
600
MAX775-FIG07
RSENSE = 0.05Ω
MAXIMUM OUTPUT CURRENT (mA)
MAX775-fig6
2500
MAXIMUM OUTPUT CURRENT (mA)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
400
RSENSE = 0.08Ω
RSENSE = 0.09Ω
200
0
7 8 9 10 11 12 13 14 15
INPUT VOLTAGE (V)
3
4
5
6
7
INPUT VOLTAGE (V)
8
9
Figure 6. MAX774 Maximum Output Current vs. Input Voltage
(VOUT = -5V)
Figure 7. MAX775 Maximum Output Current vs. Input Voltage
(VOUT = -12V)
inductor should not be so large that the peak current
never reaches the current limit. That is:
are recommended. Make sure that the inductor’s saturation current rating is greater than ILIM(max).
[V+(min) - VSW(max)] x 12µs
L(max) ≤ _______________________________
ILIM(max)
This is only important if
VIN
1
t OFF(min)
= ___________
VOUT
6
t 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 comparator response, I LIM is the current limit (see the
Current-Sense Resistor section), and δ(I) is the allowable 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 30mΩ or lower resistance are available. To minimize radiated noise, use a torroid, pot-core, or shieldedbobbin inductor. Inductors with a ferrite core or equivalent
12
Diode Selection
The ICs’ high switching frequencies demand a highspeed 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 applications, Schottky diodes may be inadequate due to their
high leakage currents; instead, high-speed silicon
diodes may be used. At heavy loads and high temperature, the benefits of a Schottky diode’s low forward voltage may outweigh the disadvantages of its high leakage current.
Current-Sense Resistor
The current-sense resistor limits the peak switch current to 210mV/RSENSE, where RSENSE is the value of
the current-sense resistor, and 210mV is the currentsense 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.
______________________________________________________________________________________
600
500
400
300
RSENSE = 0.08Ω
RSENSE = 0.09Ω
200
600
MAX776-FIG09
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
800
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT (mA)
VOUT = -15V
VOUT = -24V
RSENSE = 0.05Ω
RSENSE = 0.06Ω
RSENSE = 0.07Ω
400
200
RSENSE = 0.08Ω
RSENSE = 0.09Ω
0
100
3
4
5
6
INPUT VOLTAGE (V)
7
3 4
5 6
7 8 9 10 11 12 13 14 15
INPUT VOLTAGE (V)
Figure 8. MAX776 Maximum Output Current vs. Input Voltage
(VOUT = -15V)
Figure 9. MAX774/MAX775/MAX776 Maximum Output Current
vs. Input Voltage (VOUT = -24V)
To choose the proper current-sense resistor, simply follow the two-step procedure outlined below:
1) Determine:
• Input voltage range, V+
• Maximum (absolute) output voltage, VOUT
• Maximum output current, ILOAD
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 magnitude less than metal-film resistors). These are available in resistance values between 5mΩ and 0.1Ω.
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 approximately 125mA of output current with a 4V input, so we
look next at the RSENSE = 70mΩ line. 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 currentsense trip levels, but not sense-resistor tolerance. The
switch on resistance is 70mΩ.
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, gatesource threshold, and gate capacitance. The drain-tosource rating must be greater than the V+ - V OUT
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 capacitance is not normally a limiting factor, but values should
be less than 1nF for best efficiency. For maximum efficiency, the MOSFET should have a very-low on-resistance at the peak current and be capable of handling
that current. The transistor chosen for the typical operating circuit has a 30V drain-source voltage limit and a
0.07Ω drain-source on-resistance at VGS = -10V.
Table 1 lists suppliers of switching transistors suitable
for use with the MAX774/MAX775/MAX776.
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 inductance and are well suited for use as current-sense
External Switching Transistor
______________________________________________________________________________________
13
MAX774/MAX775/MAX776
700
MAX776-FIG08
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
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
INDUCTORS
CAPACITORS
DIODES
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
POWER MOSFETS
CURRENT-SENSE RESISTORS
IRC
(704) 264-8861
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 significantly 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 rating equal to the peak current.
The smallest low-ESR SMT capacitors currently available are the Sprague 595D series. Sanyo OS-CON
organic semiconductor through-hole capacitors also
exhibit low ESR and are especially effective at low temperatures. Table 1 lists the phone numbers of these
and other manufacturers.
PC Layout and Grounding
(704) 264-8866
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 0.07Ω ESR typically maintains 120mVP-P
14
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:
IOUT x tOFF(min)
VOUT x IOUT x ESR
∆VP-P = _____________________ + _________________
C
VIN
Due to high current levels and fast switching waveforms, proper PC board layout is essential. Use a star
ground configuration; connect the ground lead of the
input bypass capacitor, the output capacitor, the inductor, and the GND pin of the MAX774/MAX775/MAX776
at a common point very close to the device. Additionally, 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.
______________________________________________________________________________________
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
TEMP RANGE
PIN-PACKAGE
MAX775CPA
PART
0°C to +70°C
8 Plastic DIP
MAX775CSA
MAX775C/D
MAX775EPA
MAX775ESA
MAX775MJA
MAX776CPA
MAX776CSA
MAX776C/D
MAX776EPA
MAX776ESA
MAX776MJA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
8 Plastic DIP
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
Chip Topography
OUT
GND
EXT
FB
.109"
(2.769mm)
CS
SHDN
*Contact factory for dice specifications.
REF
V+
0.080
(2.032mm)
TRANSISTOR COUNT: 442;
SUBSTRATE CONNECTED TO V+.
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.)
DIM
E
A
A1
B
C
D
E
e
H
h
L
α
H
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.197
0.189
0.157
0.150
0.050 BSC
0.244
0.228
0.020
0.010
0.050
0.016
8˚
0˚
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
4.80
5.00
3.80
4.00
1.27 BSC
5.80
6.20
0.25
0.50
0.40
1.27
0˚
8˚
21-325A
h x 45˚
D
α
A
0.127mm
0.004in.
e
A1
C
L
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
B
______________________________________________________________________________________
15
MAX774/MAX775/MAX776
Ordering Information (continued)
MAX774/MAX775/MAX776
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low IQ Inverting DC-to-DC Controllers
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.)
DIM
D1
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
E
E1
D
A3
A
A2
L
A1
INCHES
MIN
MAX
–
0.200
0.015
–
0.125
0.175
0.055
0.080
0.016
0.022
0.050
0.065
0.008
0.012
0.348
0.390
0.005
0.035
0.300
0.325
0.240
0.280
0.100 BSC
0.300 BSC
–
0.400
0.115
0.150
0˚
15˚
MILLIMETERS
MIN
MAX
–
5.08
0.38
–
3.18
4.45
1.40
2.03
0.41
0.56
1.27
1.65
0.20
0.30
8.84
9.91
0.13
0.89
7.62
8.26
6.10
7.11
2.54 BSC
7.62 BSC
–
10.16
2.92
3.81
0˚
15˚
21-324A
α
8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
C
e
B1
eA
B
eB
DIM
S1
S
E1
D
E
B2
A
MILLIMETERS
MIN
MAX
–
5.08
0.36
0.58
0.97
1.65
0.58
1.14
0.20
0.38
–
10.29
5.59
7.87
7.37
8.13
2.54 BSC
3.18
5.08
3.81
–
0.38
1.52
–
1.40
0.13
–
0˚
15˚
21-326D
α
Q
L
A
B
B1
B2
C
D
E
E1
e
L
L1
Q
S
S1
α
INCHES
MAX
MIN
0.200
–
0.023
0.014
0.065
0.038
0.045
0.023
0.015
0.008
0.405
–
0.310
0.220
0.320
0.290
0.100 BSC
0.200
0.125
–
0.150
0.060
0.015
0.055
–
–
0.005
15˚
0˚
e
L1
B1
B
C
8-PIN CERAMIC
DUAL-IN-LINE
PACKAGE
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.