MAX1972EEE+ Maxim Integrated Products, MAX1972EEE+ Datasheet - Page 13

• Manufacturer Part Number: MAX1972EEE+
• Description: IC REG STP DWN 750MA 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1972EEE+

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 1.5V, 1.8V, 2.5V, 3.3V, Adj
• Current - Output: 750mA
• Frequency - Switching: 1.4MHz
• Voltage - Input: 2.6 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

the PWM comparator’s inverting input. The PWM com-
parator turns off the internal high-side MOSFET when
this sum exceeds the integrated feedback voltage.
The internal MOSFET has a current limit of 1.2A (typ). If
the current flowing out of LX_ exceeds this maximum,
the high-side MOSFET turns off and the synchronous
rectifier MOSFET turns on. This lowers the duty cycle
and causes the output voltage to droop until the current
limit is no longer exceeded. There is also a synchro-
nous rectifier current limit of -0.85A. This is to protect
the device from current flowing into LX_. If the negative
current limit is exceeded, the synchronous rectifier is
turned off, and the inductor current continues to flow
through the high-side MOSFET body diode back to the
input until the beginning of the next cycle or until the
inductor current drops to zero.
Due to the high-switching frequency and tight output
tolerance (±1%), decoupling between IN and V
recommended. Connect a 10Ω resistor between IN and
V
Place the resistor and capacitor as close to V
possible.
To reduce the supply inrush current, soft-start circuitry
ramps up the output voltage during startup. This is
done by charging the REF capacitor with a current
source of 25µA. Once REF reaches 1.2V, the output is
in full regulation. The soft-start time is determined from:
Soft-start occurs when power is first applied, and when
EN is pulled high with power already present. The part
also goes through soft-start when coming out of under-
voltage lockout (UVLO) or thermal shutdown. The range
of capacitor values for C
If V
MAX1972 assume that the supply voltage is too low to
provide a valid output voltage, and the UVLO circuit
inhibits switching. Once V
UVLO is disabled and the soft-start sequence initiates.
A logic-enable input (EN) is provided. For normal oper-
ation, drive EN logic high. Driving EN low turns off both
outputs, and reduces the input supply current to
approximately 1µA.
CC
CC
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
and a 0.1µF ceramic capacitor from V
drops below 2.35V, the MAX1970/MAX1971/
t
SS
=
V
I
REF
REF
______________________________________________________________________________________
C
Down Regulator with POR and RSI/PFO
REF
REF
=
Undervoltage Lockout
4 8
is from 0.01µF to 1.0µF.
CC
.
×
rises above 2.4V, the
10
V
4
CC
Current Limit
×
C
Decoupling
REF
CC
Startup
Enable
to GND.
CC
CC
as
is
The input voltage is sensed for 5V (typical USB applica-
tions), and if V
put (PFO) goes high. The time from PFO going high to
the outputs going out of regulation depends on the oper-
ating output voltage and currents, and the upstream 5V
bus storage capacitor value, which is 120µF minimum
(per USB specification, version 2.0). The lower the oper-
ating voltages and currents, and the higher the storage
capacitor, the longer the elapsed time. PFO is an open-
drain output, and a 10kΩ to 100kΩ pullup resistor to
V
Power-on reset (POR) provides a system reset signal.
During power-up, POR is held low until both outputs
reach 92% of their regulated voltages, POR continues
to be held low for a delayed period, and then goes
high. This delay time (T
MAX1971 and MAX1972 have a delay of 175ms. Figure
2 is an example of a timing diagram.
The POR comparator is designed to be relatively
immune to short-duration negative-going output glitch-
es.The Typical Operating Characteristics gives a plot of
maximum transient duration vs. POR comparator over-
drive. The graph was generated using a negative-going
pulse applied to an output, starting at 100mV above the
actual POR threshold, dropping below the POR thresh-
old by the percentage indicated as comparator over-
drive, and then returning to 100mV above the
threshold. The graph indicates the maximum pulse
width the output transient can have without causing
POR to trip low.
Reset input (RSI) is an input on the MAX1971 that,
when driven high, forces the POR to go low. When RSI
goes low, POR goes through a delay time identical to a
power-up event. See Figure 2 for timing diagram. RSI
allows software to command a system reset. RSI must
be high for a minimum period of 1µs in order to initiate
the POR.
Thermal-overload protection limits total power dissipa-
tion. When the IC’s junction temperature exceeds T
+170°C, a thermal sensor shuts down the device,
allowing the IC to cool. The thermal sensor turns the
part on again after the junction temperature cools by
20°C. This results in a pulsed output during continuous
overload conditions.
During a thermal event, POR goes low, PFO goes high,
and soft-start is reset.
CC
, or either output, is recommended.
CC
drops below 3.94V, the power-fail out-
Thermal-Overload Protection
D
) for MAX1970 is 16.6ms. The
Power-Fail Output
Power-On Reset
Reset Input
J
13
=