Rainbow Electronics MAX8620 - Manual (Page 12)

MAX8620Y
Reset Output (
RESET
)
RESET is an open-drain, active-low output that indi-
cates the status of OUT1. RESET is typically pulled up
through a 100k
Ω resistor to the system logic voltage.
RESET asserts at power-up. The reset timer begins
once V
OUT1 reaches 87% of regulation. RESET
deasserts 60ms after V OUT1 rises above 87% (typ) of
regulation (see the Typical Operating Characteristics).
RESET also asserts when OUT1 is disabled.
Reference Bypass Capacitor Node (BP)
An optional 0.01µF bypass capacitor at BP creates a
lowpass filter for LDO noise reduction. OUT1 and OUT2
exhibit 45µV
RMS
of output-voltage noise with C
BP
=
0.01µF and C OUT1 = C OUT2 = 4.7µF.
Undervoltage Lockout
V IN1 = V IN2 must exceed the 2.85V typical undervolt-
age-lockout threshold (V UVLO ) before the MAX8620Y
enables OUT3 to begin power-supply sequencing (see
the Power-Supply Sequencing section). The UVLO
threshold hysteresis is typically 0.5V.
Current Limiting
The MAX8620Y 300mA LDOs limit their output current to
I
LIM_ = 550mA (typ). If the LDO output current exceeds
I LIM_ , the corresponding LDO output voltage drops. The
step-down converter limits I
LIM3P
to 675mA (min).
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX8620Y. Independent thermal-protection
circuits monitor the step-down converter and the linear-
regulator circuits. When the MAX8620Y junction temper-
ature exceeds T
J = +160°C, the thermal-overload
protection circuit disables the corresponding circuitry,
allowing the IC to cool. The thermal-overload protection
circuitry enables the MAX8620Y after the junction tem-
perature cools by 15°C, resulting in a pulsed output dur-
ing continuous thermal-overload conditions. Thermal-
overload protection safeguards the MAX8620Y in the
event of fault conditions. For continuous operation, do
not exceed the absolute-maximum junction-tempera-
ture rating of T
J = +150°C.
Applications Information
Power-On Closed-Loop System
When the MAX8620Y is used in conjunction with a
microcontroller, HF_PWR and PWR_ON can implement
a short-key power-on closed-loop system (
Figure 5).
The MAX8620Y detects a rising edge at HF_PWR and
generates an internal 1.31s (typ) one-shot pulse that
begins power sequencing and temporarily enables
OUT1, OUT2, and OUT3 (depending on the state of
EN2). The 1.31s of power provides time for the proces-
sor to initialize and assert a logic-high at PWR_ON.
Once PWR_ON is driven high, OUT3, OUT1, and OUT2
(depending on the state of EN2) remain enabled. If the
microcontroller does not drive PWR_ON high during
t
HF , the MAX8620Y disables OUT1, OUT2, and OUT3,
and reenters shutdown.
µPMIC for Microprocessors or DSPs
in Portable Equipment
12 ______________________________________________________________________________________
PWR_ON
µP
POWER-ON
KEY
POWER-HOLD SIGNAL
HF_PWR
V
CORE
V
I/O
V ANA
1M Ω
PWR HOLD
MAX8620Y
Figure 5. Short-Key Power-On Closed-Loop System