MAX1702BETX+ Maxim Integrated Products, MAX1702BETX+ Datasheet - Page 13

• Manufacturer Part Number: MAX1702BETX+
• Description: IC PWR MNG TRPL OUT 36-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1702BETX+

• Applications: Processor
• Voltage - Supply: 2.6 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The MAX1702B triple-output step-down DC-DC convert-
er is ideal for powering PDA, palmtop, and subnotebook
computers. Normally, these devices require separate
power supplies for the processor core, memory, and the
peripheral circuitry. The MAX1702B’s REG1 provides a
fixed 3.3V output designed to power the microprocessor
I/O and other peripheral circuitry. REG1 delivers up to
900mA output current. The microprocessor core is pow-
ered from REG2, which has an adjustable 0.7V to V
OUTOK
RSO
LBO
ON2
DBI
MR
LBI
REFERENCE
DETECTOR
DETECTOR
CONTROL
BANDGAP
BATTERY
BATTERY
ON/OFF
DEAD-
LOGIC
RESET
TIMER
GND
LOW-
______________________________________________________________________________________
Triple-Output Power-Management IC for
MAX1702B
Detailed Description
DBO
REF
Functional Diagram
EN
REF
POK
EN
REF
EN
REF
DC-DC BUCK
DC-DC BUCK
DC-DC BUCK
1MHz PWM
1MHz PWM
1MHz PWM
WITH SKIP
WITH SKIP
WITH SKIP
REG1
REG2
REG3
IN
Microprocessor-Based Systems
INP1
LX1
PG1
OUT1
COMP1
INP2
LX2
PG2
FB2
COMP2
INP3
LX3
PG3
OUT3
COMP3
PGM3
IN
output, providing up to 400mA output current. The third
output, REG3, is designed to power memory. REG3 out-
put voltage is set to one of 3 voltages; 3.3V (PGM3 =
IN), 2.5V (PGM3 = REF), or 1.8V (PGM3 = GND) and
delivers up to 800mA of output current. All three regula-
tors utilize a proprietary regulation scheme allowing
PWM operation at medium to heavy loads, and automat-
ically switch to pulse skipping at light loads for
improved efficiency. Under low-battery conditions, the
MAX1702B issues a warning (LBO output).
The MAX1702B employs PWM control at medium and
heavy loads, and skip mode at light loads (below
approximately 80mA) to improve efficiency and reduce
quiescent current to 485µA. During skip operation, the
MAX1702B switches only as needed to service the load,
reducing the switching frequency and associated losses
in the internal switch, the synchronous rectifier, and the
external inductor.
There are three steady-state operating conditions for the
MAX1702B. The device performs in continuous conduc-
tion for heavy loads. The inductor current becomes dis-
continuous at light loads, requiring the synchronous
rectifier to be turned off before the end of a cycle as the
inductor current reaches zero. The device enters into
skip mode when the converter output voltage exceeds
its regulation limit before the inductor current reaches
the pulse-skip threshold.
During skip mode, a switching cycle initiates when the
output voltage drops below the regulation voltage. The
P-channel MOSFET switch turns on and conducts cur-
rent to the output-filter capacitor and load until the
inductor current reaches the pulse-skip current thresh-
old. Then the main switch turns off, and the current flows
through the synchronous rectifier to the output-filter
capacitor and the load. The synchronous rectifier is
turned off when the inductor current approaches zero.
The MAX1702B waits until the output voltage drops below
the regulation voltage again to initiate the next cycle.
If the inductor current does not rise sufficiently to sup-
ply the load during the on-time, the switch remains on,
allowing operation up to 100% duty cycle. This allows
the output voltage to maintain regulation while the input
voltage approaches the regulation voltage. Dropout
voltage is the output current multiplied by the on-resis-
tance of the internal switch and inductor, approximately
220mV for an 800mA load for REG1 and REG3 and
150mV for a 400mA load on REG2.
Near dropout, the on-time may exceed one PWM clock
cycle; therefore, small amplitude subharmonic ripple
can occur in the output voltage. During dropout, the
100% Duty-Cycle Operation
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