MAX866 Maxim, MAX866 Datasheet - Page 7

• Manufacturer Part Number: MAX866
• Description: 3.3V/5V or Adjustable-Output / Single-Cell DC-DC Converters
• Manufacturer: Maxim

The MAX866/MAX867 combine a switch-mode regula-
tor, N-channel power MOSFET, precision voltage refer-
ence, and power-fail detector in a single monolithic
device. The MOSFET is a “sense-FET” type for best effi-
ciency, and has a very low gate threshold voltage to
ensure start-up with low battery voltages (0.8V typ).
The MAX866/MAX867 control scheme (Figure 1) com-
bines low-voltage efficiency (80% typ) with low battery
Figure 1. Block Diagram
_______________Detailed Description
SHDN
3/5*
LBO
LBI
*MAX866 ONLY
**MAX867 ONLY
MAXIMUM
ONE-SHOT
ON-TIME
_______________________________________________________________________________________
TRIG
PFM Control Scheme
ONE-SHOT
MINIMUM
ONE-SHOT
OFF-TIME
Operating Principle
MAX866/MAX867
Q
N
Q
S
ONE-SHOT
ERROR COMPARATOR
F/F
LBI COMPARATOR
R
3.3V/5V or Adjustable-Output,
CURRENT-LIMIT
Single-Cell DC-DC Converters
COMPARATOR
TRIG
Q
drain (100µA typ). There is no oscillator; switching is
accomplished by a pair of one shots that set a maxi-
mum LX on-time (4.5µs typ) and a minimum LX off-time
(1µs). LX on-time will be terminated early if the inductor
current reaches 0.5A before 4.5µs elapses. With the
standard application circuit (Figure 2a), LX current is
typically less than 50mA, so LX on-time is normally not
terminated by the 0.5A limit and lasts the complete
4.5µs. The LX on-resistance is typically 1Ω to minimize
switch losses. The MAX866/MAX867 switching frequen-
cy depends on load, input voltage, and inductor value,
and it can range up to 250kHz with typical component
values.
REFERENCE
N
*
*
GND
REF
LX
OUT
FB**
V
**
**
V
BATT
OUT
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