MAX1954AEUB-T Maxim Integrated Products, MAX1954AEUB-T Datasheet - Page 7

• Manufacturer Part Number: MAX1954AEUB-T
• Description: Current Mode PWM Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1954AEUB-T

• Number Of Outputs: 1
• Duty Cycle (max): 93 %
• Output Voltage: 0.8 V to 4.95 V
• Output Current: 25000 mA
• Mounting Style: SMD/SMT
• Package / Case: uSOP-10
• Switching Frequency: 360 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• Topology: Boost, Buck
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The MAX1954A single-output, current-mode, PWM, step-
down DC-DC controller features foldback current limit
and switches at 300kHz for high efficiency. The
MAX1954A is designed to drive a pair of external N-
channel power MOSFETs in a synchronous buck topolo-
gy to improve efficiency and cost compared with a
P-channel power-MOSFET topology. The on-resistance
of the low-side MOSFET is used for short-circuit current-
limit sensing, while the high-side MOSFET’s on-resis-
tance is used for current-mode feedback, thus
eliminating the need for current-sense resistors. The
short-circuit current limit is fixed at 135mV. The foldback
current scheme reduces the input current during short-
circuit and severe-overload conditions. The MAX1954A
is configured with a high-side drain input (HSD) allowing
an extended input voltage range of 3V to 13.2V that is
independent of the IC input supply (Figure 1).
PIN
10
1
2
3
4
5
6
7
8
9
NAME
COMP
PGND
GND
HSD
BST
DH
DL
FB
LX
IN
High-Side Drain Current-Sense Input. HSD senses the voltage at the drain of the high-side, N-channel MOSFET.
Connect to the high-side MOSFET drain using a Kelvin connection.
Compensation and Shutdown Control Pin. Connect appropriate RC networks to compensate the control loop.
Pull to GND to shut down the IC. See the Compensation Design section for instructions on calculating the RC
values.
Feedback Input. Regulates at V
GND to set the output voltage.
Ground
IC Supply Voltage. Provides power for the IC. Connect to a 3V to 5.5V power supply. Bypass to GND with a
0.22µF ceramic capacitor and to PGND with a 1µF ceramic capacitor.
Low-Side Gate-Drive Output. Drives the synchronous-rectifier MOSFET. Swings from 0 to V
shutdown and UVLO.
Power Ground
High-Side Gate-Drive Output. Drives the high-side N-channel MOSFET. DH is a floating driver output that swings
from V
Controller Current-Sense Input. Connect LX to the junction of the MOSFETs and inductor. LX is the reference
point for the current limit.
High-Side MOSFET Supply Input. Connect a 0.1µF ceramic capacitor from BST to LX to supply the necessary
gate drive for the high-side N-channel MOSFET.
_______________________________________________________________________________________
Controller with Foldback Current Limit
Detailed Description
LX
to V
BST
Low-Cost, Current-Mode PWM Buck
. DH is low in shutdown and UVLO.
FB
= 0.8V. Connect FB to the center tap of a resistor-divider from the output to
The MAX1954A step-down converter uses a PWM, cur-
rent-mode control scheme. An internal transconductance
amplifier establishes an integrated error voltage. An
open-loop comparator compares the integrated voltage-
feedback signal against the amplified current-sense sig-
nal plus the slope compensation ramp, which is summed
into the main PWM comparator to preserve inner-loop sta-
bility and eliminate inductor staircasing. At each rising
edge of the internal clock, the high-side MOSFET turns on
until the PWM comparator trips or the maximum duty
cycle is reached. During this on-time, current ramps up
through the inductor, storing energy in a magnetic field
and sourcing current to the output. The current-mode
feedback system regulates the peak inductor current as a
function of the output-voltage error signal. The circuit acts
as a switch-mode transconductance amplifier because
the average inductor current is close to the peak inductor
current (assuming the inductor is large enough to provide
a reasonably small ripple current). This pushes the output
inductance-capacitance filter pole normally found in a
voltage-mode PWM to a higher frequency.
FUNCTION
DC-DC Converter Control Architecture
Pin Description
IN
. DL is low in
7