Electronic Components Datasheet Search
Selected language     English  ▼


MAX877 Datasheet(PDF) 6 Page - Maxim Integrated Products

Part No. MAX877
Description  5V/3.3V/3V/Adjustable-Output, Step-Up/Step-Down DC-DC Converters
Download  12 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
Logo 

 6 page
background image
_______________Detailed Description
Operating Principle
The MAX877/MAX878/MAX879 combine a switch-mode
regulator with an NPN bipolar power switch and current
limit, a precision voltage reference, and a synchronous
rectifier—all in a single monolithic device. In shutdown
mode, the internal rectifier is completely turned off and
disconnects the load from the source. Only two external
components are required in addition to the input bypass
capacitor—a 22µH inductor, and a 100µF filter capacitor.
A minimum-off-time, current-limited, pulse-frequency-
modulation (PFM) control scheme combines the high
output power and efficiency of pulse-width modulation
(PWM) with the low quiescent currents of traditional PFM
pulse skippers.
External conditions (inductor value, load, and input volt-
age) determine the way the converter operates, as fol-
lows:
At light loads, the current through the inductor starts at
zero, rises to a peak value, and drops down to zero in
each cycle (discontinuous-conduction mode). In this
case, the switching frequency is governed by a pair of
one-shots, which set a maximum on-time inversely pro-
portional to VIN [tON = 8.8/(VIN - 0.25)] and a minimum
off-time (1.3µs for MAX877/MAX879, or 2.3µs for
MAX878). With a 22µH inductor, LX’s peak current is
about 400mA and is independent of input voltage.
Efficiency at light loads is improved because of lower
peak currents.
At very light loads
, more energy is stored in the coil
than is required by the load in each cycle. The converter
regulates by skipping entire cycles. Efficiency is typically
65% to 75% in the pulse-skipping mode. Pulse-skipping
waveforms can be irregular, and the output waveform
contains a low-frequency component. Larger, low equiv-
alent-series-resistance (ESR) filter capacitors can help
reduce the ripple voltage if needed.
At heavy loads above approximately 100mA, the con-
verter enters continuous-conduction mode, where cur-
rent always flows in the inductor. The switch ON state is
controlled on a cycle-by-cycle basis, either by the
tON(max) time or the preset current limit in the switch.
This prevents exceeding the switch current rating or sat-
urating the inductor. At very heavy loads, the inductor
current self-oscillates between this peak current limit and
some lower value governed by the minimum off-time, the
inductance value, and the input/output differential.
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
6
_______________________________________________________________________________________
FUNCTION
1
Sets switch current-limit input. Connect to IN for 1A current limit. A resistor from
ILIM to IN sets lower peak inductor currents.
2
Input supply.
3
Analog ground. Not internally connected to PGND.
PIN
ILIM
IN
4
Power ground must be low impedance; solder directly to ground plane or star
ground. Connect to AGND, close to the device.
5
1A NPN power switch collector and active-rectifier PNP emitter.
6
Voltage output. Connect filter capacitor close to pin.
7
Shutdown input disables power supply when low. Also disconnects load from
input. Threshold is set at VIN/2. Connect to IN for normal operation.
AGND
PGND
LX
8
No connect, not internally connected.
OUT
S
H
D
N
N.C.
(MAX877)
______________________________________________________________Pin Description
NAME
FB
(MAX879)
Feedback input for adjustable-output operation. Connect to an external voltage
divider between VOUT and AGND.
SEL
(MAX878)
Selects the main output voltage: 3.3V when connected to AGND, 3.0V when left
open.




Html Pages

1  2  3  4  5  6  7  8  9  10  11  12 


Datasheet Download



Related Electronics Part Number

Part NumberComponents DescriptionHtml ViewManufacturer
ST763A3.3V STEP DOWN CURRENT MODE PWM DC-DC CONVERTERS 1 2 3 4 5 MoreSTMicroelectronics
IMS77 Watt DC-DC Converters 1 2 3 4 Power-One
NMA-1Isolated 1W Dual Output DC-DC Converters 1 2 C&D Technologies
IRF7811WPower MOSFET for DC-DC Converters 1 2 3 4 5 MoreInternational Rectifier
MAX1674High-Efficiency Low-Supply-Current Compact Step-Up DC-DC Converters 1 2 3 4 5 MoreMaxim Integrated Products
MAX5025500kHz 36V Output SOT23 PWM Step-Up DC-DC Converters 1 2 3 4 5 MoreMaxim Integrated Products
SP6122Low Voltage Micro 8 PFET Buck Controller Ideal for 1A to 5A Small Footprint DC-DC Power Converters 1 2 3 4 5 MoreSipex Corporation
PTH05050DC-DC CONVERTERS POLA Non-isolated 1 2 3 4 Artesyn Technologies
71128Simple Solution for Dynamically Programming the Output Voltage of DC-DC Converters 1 2 3 4 5 MoreVishay Siliconix
NXI15081 A DC-DC Non-Isolated Converters 1 2 3 Artesyn Technologies

Link URL

Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Contact us   |   Privacy Policy   |   Bookmark   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com 2003 - 2017    


Mirror Sites
English : Alldatasheet.com  , Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp  |   Russian : Alldatasheetru.com
Korean : Alldatasheet.co.kr   |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com  |   Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl