MAX1947ETA18+T Maxim Integrated Products, MAX1947ETA18+T Datasheet - Page 7

• Manufacturer Part Number: MAX1947ETA18+T
• Description: IC DC-DC CONV 1.8V 8-TDFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1947ETA18+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.8V
• Current - Output: 250mA
• Frequency - Switching: Up to 2MHz
• Voltage - Input: 0.7 ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TDFN Exposed Pad
• Power - Output: 1.95W
• Output Voltage: 1.8 V
• Output Current: 273 mA
• Input Voltage: 0.7 V to 3.6 V
• Supply Current: 70 uA
• Switching Frequency: 650 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX1947ETA18+T

The MAX1947 is a bootstrapped design. Upon turn-on,
a startup oscillator brings the output voltage high
enough to allow the main DC-DC circuitry to run. Once
the output voltage reaches 1.62V (typ) the main DC-DC
circuitry turns on and boosts the output voltage to the
final regulation point.
The unique minimum off-time, current-limited control
scheme is the key to the MAX1947’s low operating cur-
rent and high efficiency over a wide load range. The
architecture combines the high output power and effi-
ciency of a pulse-width modulation (PWM) device with
the ultra-low quiescent current of a traditional pulse-
skipping controller. The switching frequency can be as
high as 2MHz and depends upon the load current and
input voltage. The MAX1947 is designed to operate
using low-ESR ceramic capacitors, so output voltage
ripple due to ESR is very small (approximately 10mV
The MAX1947 enters track mode when BATT is greater
than the output-voltage regulation point. Track mode
can only be entered under the following conditions:
_______________________________________________________________________________________
Step-Up DC-DC Converter with RESET
BATT
SHDN
MAX TIMER
MIN TIMER
Control Scheme
t
t
OFF
ON
OSCILLATOR
1.25V REFERENCE
SHUTDOWN
CIRCUITRY
STARTUP
GND
Track Mode
(REF)
REF
GATE DRIVERS
LOGIC AND
CONTROL
P-P
).
Low Input/Output Voltage
MAX1947
AMPLIFIER
ERROR
CURRENT-LIMIT
AMPLIFIER
V
minimum off-time expires. During track mode, the syn-
chronous rectifier is turned on 100% of the time and the
output voltage tracks the battery voltage. Track mode is
exited by V
The internal synchronous rectifier eliminates the need
for an external Schottky diode, reducing cost and board
space. During the cycle off-time, the p-channel MOSFET
turns on and shunts the MOSFET body diode. As a
result, the synchronous rectifier significantly improves
efficiency without the addition of an external compo-
nent. Conversion efficiency can be as high as 94%.
The MAX1947 features an active-low push-pull RESET
output for use with a microcontroller (µC). It signals the
µC when the MAX1947 output voltage is within operat-
ing limits. During startup, RESET is held low. When the
RESET threshold (90% of the output regulation voltage)
is reached, a 75ms (min) timer begins counting. RESET
is switched high once the timer expires.
BATT
ZERO-CROSSING
75ms TIMER
AMPLIFIER
REF
> V
0.9 x REF
OUT
OUT
*BODY DIODE CONTROL
, V
falling below the V
P*
OUT
N
PGND
Synchronous Rectification
> V
RESET
OUT
Functional Diagram
LX
OUT
regulation point, and the
OUT
regulation point.
RESET
7