MAX8668 Maxim Integrated Products, MAX8668 Datasheet - Page 11

• Manufacturer Part Number: MAX8668
• Description: (MAX8667 / MAX8668) First Dual Step-Down DC-DC Converters
• Manufacturer: Maxim Integrated Products

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loads up to 300mA. The LDOs include an internal refer-
ence, error amplifier, p-channel pass transistor, and
internal voltage-dividers. Each error amplifier compares
the reference voltage to the output voltage (divided by
the internal voltage-divider) and amplifies the differ-
ence. If the divided feedback voltage is lower than the
reference voltage, the pass-transistor gate is pulled
lower, allowing more current to pass to the outputs and
increasing the output voltage. If the divided feedback
voltage is too high, the pass-transistor gate is pulled
up, allowing less current to pass to the output.
The input voltage range of LDO regulators OUT3 and
OUT4 is 1.7V to 5.5V. This supply voltage must be less
than or equal to the voltage applied to IN12 (V
V
An undervoltage lockout circuit turns off the LDO regula-
tors when the input supply voltage is too low to guarantee
proper operation. When V
OUT3 and OUT4 are shut down. OUT3 and OUT4 turn
on and begin soft-start when V
When initially powered up, or enabled with EN_, the
LDOs soft-start by gradually ramping up the output
voltage. This reduces inrush current during startup. The
Figure 2. Timing Diagram
IN12
).
Input Supply and Undervoltage Lockout
1.5MHz Dual Step-Down DC-DC Converters
IN12
______________________________________________________________________________________
with Dual LDOs and Individual Enables
OUTx
ENx
ENy
IN34
IN34
falls below 1.5V (typ),
rises above 1.6V (typ).
OUTy
ENx, ENy ARE ANY COMBINATION OF EN1–EN4.
Soft-Start
IN34
t
PWRON
≤
soft-start ramp time is typically 100µs from the start of
the soft-start ramp to the output reaching its nominal
regulation voltage.
The OUT3 and OUT4 output current is limited to 375mA
(min). If the output current exceeds the current limit, the
corresponding LDO output voltage drops.
The maximum dropout voltage for the linear regulators
is 250mV at 300mA load. To avoid dropout, make sure
the IN34 supply voltage is at least 250mV higher than
the highest LDO output voltage.
Thermal-overload protection limits the total power dissi-
pation in the MAX8667/MAX8668. Thermal-protection
circuits monitor the die temperature. If the die tempera-
ture exceeds +160°C, the IC is shut down, allowing the
IC to cool. Once the IC has cooled by 15°C, the IC is
enabled again. This results in a pulsed output during
continuous thermal-overload conditions. The thermal-
overload protection protects the MAX8667/MAX8668 in
the event of fault conditions. For continuous operation,
do not exceed the absolute maximum junction temper-
ature of +150°C. See the Thermal Considerations sec-
tion for more information.
t
PWRON
SIGNALS FOLLOWING THE FIRST ENABLE
t
EN
IS THE PERIOD REQUIRED TO ENABLE FROM SHUTDOWN
IS THE ENABLE TIME FOR SUBSEQUENT ENABLE
t
EN
Thermal-Overload Protection
Current Limit
Dropout
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