MAX1830EEE+T Maxim Integrated Products, MAX1830EEE+T Datasheet - Page 9

• Manufacturer Part Number: MAX1830EEE+T
• Description: IC REG STEP DOWN 3A 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1830EEE+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.5V, 1.8V, 2.5V, Adj
• Current - Output: 3A
• Frequency - Switching: 1MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 1.12W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 2. Output Voltage Programming
Figure 4. Adjustable Output Voltage
In a step-down regulator without synchronous rectifica-
tion, an external Schottky diode provides a path for cur-
rent to flow when the inductor is discharging. Replacing
the Schottky diode with a low-resistance NMOS syn-
chronous switch reduces conduction losses and
improves efficiency.
The NMOS synchronous-rectifier switch turns on follow-
ing a short delay after the PMOS power switch turns off,
thus preventing cross conduction or “shoot through.” In
constant-off-time mode, the synchronous-rectifier
switch turns off just prior to the PMOS power switch
turning on. While both switches are off, inductor current
flows through the internal-body diode of the NMOS
switch. The internal-body diode’s forward voltage is rel-
atively high. An external Schottky diode from PGND to
LX can improve efficiency.
Junction-to-ambient thermal resistance, θ
dependent on the amount of copper area immediately
surrounding the IC leads. The MAX1830/MAX1831
evaluation kit has 0.7in
resistance of +71°C/W with no forced airflow. Airflow
over the board significantly reduces the junction-to-
ambient thermal resistance. For heatsinking purposes,
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Unconnected
R1 = 30kΩ
R2 = R1(V
V
FBSEL
REF
Synchronous Rectification and Internal Switches
GND
V
REF
= 1.1V
CC
OUT
MAX1830
MAX1831
/ V
REF
PIN
- 1)
Resistive divider
_______________________________________________________________________________________
Output voltage
Output voltage
Output voltage
LX
FB
Synchronous Rectification
2
FB
of copper area and a thermal
Thermal Resistance
OUTPUT VOLTAGE (V)
MAX1830
2.5
1.5
1.8
Adjustable
JA
R2
R1
, is highly
MAX1831
V
OUT
2.5
1.5
3.3
evenly distribute the copper area connected at the IC
among the high-current pins.
Power dissipation in the MAX1830/MAX1831 is domi-
nated by conduction losses in the two internal power
switches. Power dissipation due to supply current in the
control section and average current used to charge
and discharge the gate capacitance of the internal
switches (i.e., switching losses) is approximately:
where C = 5nF and f
cy in PWM mode.
This number is reduced when the switching frequency
decreases as the part enters Idle Mode. Combined con-
duction losses in the two power switches are approxi-
mated by:
where R
The junction-to-ambient thermal resistance required to
dissipate this amount of power is calculated by:
where:
θ
T
T
P
For typical applications, use the recommended compo-
nent values in Table 1. For other applications, take the
following steps:
1) Select the desired PWM-mode switching frequency;
2) Select the constant off-time as a function of input
3) Select R
4) Select the inductor as a function of output voltage,
The output of the MAX1830/MAX1831 is selectable
between one of three preset output voltages. For a pre-
set output voltage, connect FB to the output voltage
and connect FBSEL as indicated in Table 2. For an
adjustable output voltage, connect FBSEL to GND and
connect FB to a resistive divider between the output
JA
J,MAX
A,MAX
D(TOT)
1MHz is a good starting point. See Figure 3 for maxi-
mum operating frequency.
voltage, output voltage, and switching frequency.
off-time, and peak-to-peak inductor current.
= junction-to-ambient thermal resistance
= maximum junction temperature
= maximum ambient temperature
PMOS
= total losses
TOFF
θ
JA
is the on-resistance of the PMOS switch.
= (T
P
as a function of off-time.
P
DS
D
J,MAX
= I
Setting the Output Voltage
= C x V
PWM
OUT 2
- T
Design Procedure
A,MAX
IN 2
is the switching frequen-
x R
Power Dissipation
x f
PMOS
) / P
PWM
D(T
OT
)
9