MAX15051EWE+T Maxim Integrated Products, MAX15051EWE+T Datasheet - Page 10

• Manufacturer Part Number: MAX15051EWE+T
• Description: Switching Converters, Regulators & Controllers 4A DC/DC CONVTR egulator with Integr
• Manufacturer: Maxim Integrated Products

Specifications of MAX15051EWE+T

• Output Current: 4 A
• Input Voltage: 2.9 V to 5.5 V
• Switching Frequency: 1 MHz
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 96 %
• Package / Case: WLP-16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Efficiency, 4A, 1MHz, Step-Down Regulators
with Integrated Switches in 2mm x 2mm Package
turns off when the ramp voltage exceeds the V
signal or the current-limit threshold is exceeded. The
low-side switch then turns on for the remainder of the
oscillator cycle.
The MAX15050 features a skip function. In skip mode,
the MAX15050 switches only as necessary to maintain
the output at light loads (not capable of sinking current
from the output). This maximizes light-load efficiency
and reduces the input quiescent current.
In skip mode, the low-side switch is turned off when the
inductor current decreases to 0.2A (typ) to ensure no
reverse current flowing from the output capacitor.
The high-side switch minimum on-time is controlled to
guarantee that 0.9A current is reached to avoid high
frequency bursts at no-load conditions, which prevents
a rapid increase of the supply current caused by addi-
tional switching losses. Under heavy load, the device
operates as a PWM converter.
The internal, high-side MOSFET has a typical 8A peak
current-limit threshold. When current flowing out of LX
exceeds this limit, the high-side MOSFET turns off and
the low-side MOSFET turns on. The low-side MOSFET
remains on until the inductor current falls below the low-
side current limit. This lowers the duty cycle and caus-
es the output voltage to droop until the current limit is
no longer exceeded. The MAX15050/MAX15051 use a
hiccup mode to prevent overheating during short-cir-
cuit output conditions.
During current limit, if V
V
or more, the device enters hiccup mode. The high-side
MOSFET and the low-side MOSFET turn off and both
COMP and REFIN/SS are internally pulled low. The
device remains in this state for 896 clock cycles and
then attempts to restart for 112 clock cycles. If the fault-
causing current limit has cleared, the device resumes
normal operation. Otherwise, the device reenters hic-
cup mode.
The MAX15050/MAX15051 utilize an adjustable soft-
start function to limit inrush current during startup. An
8µA (typ) current source charges an external capacitor
connected to REFIN/SS. The soft-start time is adjusted
by the value of the external capacitor from REFIN/SS to
GND. The required capacitance value is determined as:
10
Soft-Start and Reference Input (REFIN/SS)
REFIN/SS
______________________________________________________________________________________
and stays below this level for typically 36µs
Skip Mode (MAX15050)
FB
drops below 70% of
Current Limit
COMP
Figure 2. Typical Soft-Start Implementation with External
Reference
where t
Connect a minimum 1nF capacitor between REFIN/SS
and GND. REFIN/SS is also an external reference input
(REFIN/SS). The device regulates FB to the voltage
applied to REFIN/SS. The internal soft-start is not avail-
able when using an external reference. Figure 2 shows
a method of soft-start when using an external refer-
ence. If an external reference is not applied, the device
uses the internal 0.6V reference.
The UVLO circuitry inhibits switching when V
below 2.55V (typ). Once V
UVLO clears and the soft-start function activates. A
50mV hysteresis is built-in for glitch immunity.
The gate-drive voltage for the high-side, n-channel
switch is generated by a flying-capacitor boost circuit.
The capacitor between BST and LX is charged from the
V
low-side MOSFET is switched off, the voltage of the
capacitor is stacked above LX to provide the necessary
turn-on voltage for the high-side internal MOSFET.
PWRGD is an open-drain output that goes high
impedance when V
V
is below 90% of V
or V
shutdown.
IN
REFIN/SS
supply while the low-side MOSFET is on. When the
REFIN/SS
SS
R1
is above 0.54V. PWRGD pulls low when V
is the required soft-start time in seconds.
R2
is below 0.54V. PWRGD is low during
Undervoltage Lockout (UVLO)
Power-Good Output (PWRGD)
REFIN/SS
FB
C
is above 92.5% x V
=
C
8
µ
A t
0 6
for at least 48 clock cycles
DD
.
×
V
rises above 2.6V (typ),
SS
REFIN/SS
MAX15050
MAX15051
REFIN/SS
DD
BST
and
FB
is