MAX770 Maxim Integrated Products, MAX770 Datasheet

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MAX770

Manufacturer Part Number
MAX770
Description
Manufacturer
Maxim Integrated Products
Datasheet

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19-0202; Rev 2; 11/96
The MAX770–MAX773 step-up switching controllers pro-
vide 90% efficiency over a 10mA to 1A load. A
unique current-limited pulse-frequency-modulation (PFM)
control scheme gives these devices the benefits of
pulse-width-modulation (PWM) converters (high efficiency
at heavy loads), while using less than 110µA of supply
current (vs. 2mA to 10mA for PWM converters).
These ICs use tiny external components. Their high
switching frequencies (up to 300kHz) allow surface-
mount magnetics of 5mm height and 9mm diameter.
The MAX770/MAX771/MAX772 accept input voltages
from 2V to 16.5V. Output voltages are preset at 5V,
(MAX770), 12V (MAX771), and 15V (MAX772); they can
also be adjusted using two resistors.
The MAX773 accepts inputs from 3V to 16.5V. For a wider
input range, it features an internal shunt regulator that
allows unlimited higher input voltages. The MAX773’s out-
put can be set to 5V, 12V, or 15V, or it can be adjusted
with two resistors.
The MAX770–MAX773 drive external N-channel MOSFET
switches, allowing them to power loads up to 15W. If less
power is required, use the MAX756/MAX757 or
MAX761/MAX762 step-up switching regulators with on-
board MOSFETs.
________________________Applications
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
__________Typical Operating Circuit
_______________General Description
2V TO V OUT
INPUT
ON/OFF
Palmtops/Handy-Terminals
High-Efficiency DC-DC Converters
Battery-Powered Applications
Positive LCD-Bias Generators
Portable Communicators
Flash Memory Programmers
SHDN
REF
5V/12V/15V or Adjustable, High-Efficiency,
________________________________________________________________ Maxim Integrated Products
FB AGND GND
MAX771
EXT
CS
V+
N
Low I
OUTPUT
12V
Q
, Step-Up DC-DC Controllers
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
**Contact factory for availability and processing to MIL-STD-883B.
____________________________Features
_________________Pin Configurations
______________Ordering Information
MAX770CPA
MAX770CSA
MAX770C/D
MAX770EPA
MAX770ESA
MAX770MJA
Pin Configurations continued at end of data sheet.
TOP VIEW
90% Efficiency for 10mA to 1A Load Currents
Up to 15W Output Power
110µA Max Supply Current
5µA Max Shutdown Current
2V to 16.5V Input Range
(MAX770/MAX771/MAX772)
Internal Shunt Regulator for High Input Voltages
(MAX773)
Preset or Adjustable Output Voltages
Current-Limited PFM Control Scheme
300kHz Switching Frequency
PART
MAX770: 5V or Adjustable
MAX771: 12V or Adjustable
MAX772: 15V or Adjustable
MAX773: 5V, 12V, 15V, or Adjustable
SHDN
EXT
V+
FB
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
1
2
3
4
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
MAX770
MAX771
MAX772
DIP/SO
8
7
6
5
CS
GND
AGND
REF
PIN-PACKAGE
Plastic DIP
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP**
1

Related parts for MAX770

MAX770 Summary of contents

Page 1

... The MAX770/MAX771/MAX772 accept input voltages from 2V to 16.5V. Output voltages are preset at 5V, (MAX770), 12V (MAX771), and 15V (MAX772); they can also be adjusted using two resistors. The MAX773 accepts inputs from 3V to 16.5V. For a wider input range, it features an internal shunt regulator that allows unlimited higher input voltages. The MAX773’ ...

Page 2

... MAX77_C_ _/E_ _ ..........................................................+150°C MAX77_MJ_..................................................................+175°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C , unless otherwise noted. Typical values are at T CONDITIONS MAX770–772 (internal feedback resistors) MAX770–772C/E (external resistors) MAX770–772MJA (external resistors) MAX773C/E MAX773MJD MAX770/MAX771/MAX772 V+ = 16.5V, SHDN = 0V (normal operation 10.0V, SHDN ≥ ...

Page 3

Adjustable, High-Efficiency, ELECTRICAL CHARACTERISTICS (continued) ( 0mA LOAD A MIN PARAMETERS SYMBOL REF Load Regulation REF Line Regulation FB Trip-Point Voltage V FB Input Current I SHDN Input High ...

Page 4

... 12V 60 OUT CIRCUIT OF FIGURE 2b 50 0.001 0.01 0.1 1 OUTPUT CURRENT (A) MAX770 LOAD CURRENT vs. MINIMUM START-UP INPUT VOLTAGE 700 OUT 600 CIRCUIT OF FIGURE 2a 500 400 300 ABOVE 3.4V, THE CIRCUIT 200 STARTS UP UNDER MAXIMUM 100 LOAD CONDITIONS 0 1.0 1.5 2.0 2.5 3.0 3 ...

Page 5

Adjustable, High-Efficiency, ____________________________Typical Operating Characteristics (continued +25°C, unless otherwise noted.) A REFERENCE OUTPUT RESISTANCE vs. TEMPERATURE 250 200 150 100 50 0 -60 -40 - TEMPERATURE ( C) MAXIMUM SWITCH ON-TIME vs. TEMPERATURE 16.5 ...

Page 6

... TO 4.5V, 2V/div RIPPLE, 100mV/div, AC-COUPLED OUT _______________________________________________________________________________________ 6 LIGHT-LOAD SWITCHING WAVEFORMS A I LIM 3V 165mA OUT A: EXT VOLTAGE, 5V/div B: INDUCTOR CURRENT, 1A/div C: V RIPPLE 100mV/div, AC-COUPLED OUT LOAD-TRANSIENT RESPONSE LOAD CURRENT 0.5A/div ( RIPPLE, 100mV/div, AC-COUPLED OUT MAX770 s/div MAX770 A B 2ms/div ...

Page 7

... EXT Gate drive for external N-channel power transistor Power-supply input. Also acts as a voltage-sense point when in bootstrapped mode for the MAX770/MAX771/MAX772 shunt regulator when SGND is connected to ground for the MAX773. Bypass to SGND with 0.1 F when using the shunt regulator. Feedback input for adjustable-output operation. Connect to ground for fixed-output operation. Use ...

Page 8

... MOSFET’s gate capacitance. The minimum input voltage for the MAX770–MAX773 is 3V when using external feedback resistors. With supply voltages below 5V, bootstrapped mode is recommended. Note: When using the MAX770/MAX771/MAX772 in ...

Page 9

... LOW-VOLTAGE OSCILLATOR CURRENT-SENSE AMPLIFIER 0.2V The MAX770–MAX773 use a proprietary current-limited PFM control scheme to provide high efficiency over a wide range of load currents. This control scheme com- bines the ultra-low supply current of PFM converters (or pulse skippers) with the high full-load efficiency of PWM converters. ...

Page 10

... As with traditional PFM converters, the power transistor is not turned on until the voltage comparator senses that the output is out of regulation. However, unlike tra- ditional PFM converters, the MAX770–MAX773 switch using the combination of a peak current limit and a pair of one-shots that set the maximum on-time (16µs) and ...

Page 11

Adjustable, High-Efficiency V12 14 V15 SGND R4 8 63.4k REF MAX773 (1 LBO 0 LBI 13 EXTH EXTL SHDN 10k ...

Page 12

... V = 1.5V REF Figure 4. MAX773 Shunt Regulator The MAX770/MAX771/MAX772 feature a low input volt- age start-up oscillator that guarantees start-up with no load down to 2V when operating in bootstrapped mode and using internal feedback resistors. At these low volt- ages, the supply voltage is not large enough for proper error-comparator operation and internal biasing ...

Page 13

... In Figure 3b, the resistor in series with EXTH limits the base current, and EXTL (which is connected directly to the base) turns the transistor off. When SHDN is high, the MAX770–MAX773 enter shut- down mode. In this mode, the internal biasing circuit turned off (including the reference) and V ...

Page 14

... This provides adequate biasing SHUNT current for this circuit, although higher shunt currents can be used. ______________________________________________________________________________________ 14 BOOTSTRAPPED* GND to V OUT Lower Higher Higher 2V to 16.5V (MAX770/MAX771/MAX772), (internal feedback resistors 16.5V (MAX770/MAX771/MAX772), (external feedback resistors 16.5V (MAX773 (MAX770/MAX771/MAX772 (MAX773) MAX770–MAX773(N) MAX770–MAX773( SHUNT V+ ...

Page 15

Adjustable, High-Efficiency, 3 OUT 3 40m SENSE 2 50m SENSE 2.0 R SENSE 1.5 1.0 R SENSE 0.5 R SENSE INPUT VOLTAGE (V) Figure ...

Page 16

... L Table 2 lists inductor suppliers and specific recom- mended inductors. N Use an N-channel MOSFET power transistor with the MAX770/MAX771/MAX772 (Figure 8a). Use an N-FET whenever possible with the MAX773. An NPN transistor can be used, but be extremely careful R SENSE when determining the base current (see NPN Transistors section) ...

Page 17

... T voltage and a high current gain. A good transistor to use is the Zetex ZTX694B. The MAX770–MAX773’s high switching frequency of TH demands a high-speed rectifier. Schottky diodes such as the 1N5817–1N5822 are recommended. Make sure NPN Transistors that the Schottky diode’ ...

Page 18

... The input bypass capacitor (C1) reduces peak currents drawn from the voltage source and also reduces noise at the voltage source caused by the switching action of the MAX770–MAX773. The input voltage source imped- ance determines the size of the capacitor required at the V+ input. As with the output filter capacitor, a low- ESR capacitor is recommended. For output currents up to 1A, 150µ ...

Page 19

... The Typical Operating Characteristics show the Start- Up Voltage vs. Load Current graph for bootstrapped- mode operation. This graph depends on the type of power switch used. The MAX770–MAX773 are not designed to start up under full load in boot- strapped mode with low input voltages. Layout Considerations ...

Page 20

... Plastic DIP 14 Narrow SO 14 CERDIP TRANSISTOR COUNT: 501; SUBSTRATE CONNECTED TO V+. V+ LBO V15 EXTH EXTL LBI CS SGND GND FB REF TRANSISTOR COUNT: 501; SUBSTRATE CONNECTED TO V+. MAX770/MAX771/MAX772 EXT CS 0.126" (3.200mm) GND AGND SHDN REF 0.080" (2.032mm) MAX773 V5 V12 V15 EXTH EXTL CS SGND 0.126" ...

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