MP1497 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
For example, when connecting VIN to a 12V
source, RPULLUP≥[(12V – 6.5V) ÷ 100µA = 55kꢀ].
OPERATION
The MP1497 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with built-in power MOSFETs. It offers a very
compact solution to achieve 3A continuous
output current with excellent load and line
regulation over a wide input supply range.
Connecting the EN pin directly to a voltage
source without any pullup resistor requires
limiting the amplitude of the voltage source to
below 6.5V to prevent damaging the Zener
diode.
EN/SYNC
The MP1497 operates in a fixed-frequency,
peak-current–control mode to regulate the
output voltage. The internal clock initiates a
PWM cycle. The integrated high-side power
MOSFET turns on and remains on until its
current reaches the value set by the COMP
voltage. When the power switch is off, it
remains off until the next clock cycle starts. If
the current in the power MOSFET does not
reach the COMP set current value within 95%
of one PWM period, the power MOSFET will be
forced to turn off.
Zener
6.5V-typ
EN LOGIC
GND
Figure 2: Zener Diode Circuit
For external clock synchronization, connect a
clock with a frequency range of 200kHz and
2MHz 2ms after the output voltage is set: The
internal clock rising edge will synchronize with
the external clock rising edge. Select an
external clock signal with a pulse-width less
than 1.7μs.
Internal Regulator
Under-Voltage Lockout
The 5V internal regulator powers most of the
internal circuitries. This regulator takes the VIN
input and operates in the full VIN range. When
VIN exceeds 5.0V, the output of the regulator is
in full regulation. When VIN is below 5.0V, the
output decreases and requires a 0.1µF ceramic
decoupling capacitor.
Under-voltage lockout (UVLO) protects the chip
from operating at an insufficient supply voltage.
The MP1497 UVLO comparator monitors the
output voltage of the internal regulator, VCC.
The UVLO rising threshold is about 3.9V while
its falling threshold is 3.25V.
External Soft-Start
Error Amplifier
Adjust the soft-start time by connecting a
capacitor from the SS pin to ground. When the
soft-start period starts, an internal 11µA current
source charges the external capacitor. The soft-
start capacitor connects to the non-inverting
input of the error amplifier. The soft-start period
lasts until the voltage on the soft-start capacitor
exceeds the reference voltage of 0.8V. At this
point, the non-inverting amplifier uses the
reference voltage. The soft-start time can be
calculated as:
The error amplifier compares the FB pin voltage
against the internal 0.8V reference (REF) and
outputs a COMP voltage that controls the
power MOSFET current. The optimized internal
compensation network minimizes the external
component counts and simplifies the control
loop design.
Enable/SYNC Control
EN is a digital control pin that turns the
regulator on and off. Drive EN high to turn on
the regulator, drive it low to turn it off. An
internal 1Mꢀ resistor from EN to GND allows
EN to float to shut down the chip.
0.8V CSS(nF)
tSS(ms)
11A
The EN pin is clamped internally using a 6.5V
series-Zener-diode as shown in Figure 2.
Connecting the EN pin through a pullup resistor
to any voltage connected to VIN limits the EN
input current to less than 100µA.
Over-Current-Protection and Hiccup
The MP1497 has a cycle-by-cycle over-current
limit that protects against the inductor current
peak value exceeding the set current limit
threshold. Under-voltage protection (UVP)
triggers if the FB voltage drops below the
MP1497 Rev. 1.06
9/7/2015
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