Rainbow Electronics MAX8621Z User Manual
Page 11
Power-Supply Sequence
BUCK1 is always first on and last off in the MAX8621Y/
MAX8621Zs’ power sequence. BUCK1 turns on approxi-
mately 40µs after PWRON is enabled. BUCK2 turns on
approximately 40µs after BUCK1, and OUT1 turns on
65µs after BUCK2. These delays have been added to
sequence the turn-on of the step-down converters and
LDOs so that the initial current surges are distributed
over time. For the same reason, OUT2, OUT3, and OUT4
can be turned on by EN2, EN3, and EN4 signals, but
only after OUT1 has reached 87% of its final value. Note
that OUT2 typically requires a longer time to enable than
OUT3 and OUT4 (45µs versus 15µs). All regulators can
be turned off at the same time when PWRON is low, but
BUCK1 remains on for approximately another 120µs
after PWRON goes low.
MAX8621Y/MAX8621Z
Dual Step-Down DC-DC Power-Management ICs
for Portable Devices
______________________________________________________________________________________
11
MAX8621Y
MAX8621Z
SEL1
SEL2
OUT1 (V)
OUT2 (V)
OUT3 (V)
OUT4 (V)
OUT1 (V)
OUT2 (V)
OUT3 (V)
OUT4 (V)
IN
IN
3.3
3.3
2.85
2.85
2.8
2.6
3.0
3.0
IN
OPEN
3.0
3.3
3.3
2.85
2.6
2.6
3.0
3.0
IN
GND
2.5
3.3
2.85
3.0
2.6
2.6
2.9
2.9
OPEN
IN
2.85
3.3
3.0
2.5
2.6
2.6
3.0
3.3
OPEN
OPEN
3.3
3.3
2.8
3.0
2.6
2.6
1.8
3.0
OPEN
GND
3.3
3.3
3.0
3.0
2.6
2.6
2.8
3.0
GND
IN
3.3
2.85
3.3
2.85
2.9
3.1
1.8
1.5
GND
OPEN
2.85
2.85
3.3
3.3
3.0
2.9
2.9
2.9
GND
GND
3.3
2.85
3.0
3.0
3.0
2.5
2.9
2.9
Table 1. SEL1 and SEL2, MAX8621Y/MAX8621Z Output Voltage Selection
PWRON
BUCK2
OUT1
BUCK1
REF
EN2
OUT3
(OUT4)
EN3
(EN4)
OUT2
RESET
15
µs
65
µs
40
µs
87% REGULATION
87% REGULATION
60ms
45
µs
120
µs
40
µs
Figure 2. Power-On/Off Sequence Diagram