MAX1951ESA+TW Maxim Integrated Products, MAX1951ESA+TW Datasheet - Page 8

• Manufacturer Part Number: MAX1951ESA+TW
• Description: DC/DC Switching Regulators 1MHz 2A 2.6-5.5V PWM DC/DC Step-Down
• Manufacturer: Maxim Integrated Products

Specifications of MAX1951ESA+TW

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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. The MAX1951/MAX1952
utilize a pulse-skip mode to prevent overheating during
short-circuit output conditions. The device enters pulse-
skip mode when the FB voltage drops below 300mV, lim-
iting the current to 3A (typ) and reducing power
dissipation. Normal operation resumes upon removal of
the short-circuit condition.
Due to the high switching frequency and tight output
tolerance (1%), decouple V
connected from V
nected from V
V
The MAX1951/MAX1952 employ digital soft-start circuitry
to reduce supply inrush current during startup conditions.
When the device exits undervoltage lockout (UVLO), shut-
down mode, or restarts following a thermal-overload
event, or the external pulldown on COMP is released, the
digital soft-start circuitry slowly ramps up the voltages at
REF and FB (see the Soft-Start Waveforms in the Typical
Operating Characteristics).
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
Figure 1. Functional Diagram
8
CC
_______________________________________________________________________________________
as possible.
CC
to IN. Place the capacitor as close to
CC
to GND, and a 10Ω resistor con-
COMP
V
CC
CC
with a 0.1µF capacitor
RAMP GEN
MAX1951
V
CLAMP
OSC
CC
Decoupling
CURRENT SENSE
SLOPE
COMP
Soft-Start
SOFT-START/
POSITIVE AND NEGATIVE CURRENT LIMITS
BANDGAP
UVLO
1.25V
GND
REF
ERROR
SIGNAL
DAC
CLOCK
If V
switching. Once V
clears, and the soft-start sequence activates.
The output of the internal transconductance voltage
error amplifier connects to COMP. The normal operation
voltage for COMP is 1V to 2.2V. To shut down the
MAX1951/MAX1952, use an NPN bipolar junction
transistor or a very low output capacitance open-drain
MOSFET to pull COMP to GND. Shutdown mode causes
the internal MOSFETs to stop switching, forces LX to a
high-impedance state, and shorts REF to GND.
Release COMP to exit shutdown and initiate the soft-
start sequence.
Thermal-overload protection limits total power dissipation
in the device. When the junction temperature exceeds T
= +160°C, a thermal sensor forces the device into shut-
down, allowing the die to cool. The thermal sensor turns
the device on again after the junction temperature cools
by 15°C, resulting in a pulsed output during continuous
overload conditions. Following a thermal-shutdown condi-
tion, the soft-start sequence begins.
SHUTDOWN
THERMAL
CC
REF
2V
drops below 2.25V, the UVLO circuit inhibits
CONTROL
PWM
g
m
Thermal-Overload Protection
CC
rises above 2.35V, the UVLO
Undervoltage Lockout
IN
LX
PGND
FB
REF
and Shutdown Mode
Compensation
J