MAX1842EEE Maxim Integrated Products, MAX1842EEE Datasheet - Page 11

• Manufacturer Part Number: MAX1842EEE
• Description: DC/DC Switching Regulators
• Manufacturer: Maxim Integrated Products

Specifications of MAX1842EEE

• Case: ssop
• Dc: 02+
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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.
Junction-to-ambient thermal resistance, θ
dependent on the amount of copper area immediately
surrounding the IC leads. The MAX1742 evaluation kit
has 0.5in
80°C/W with no forced airflow. Airflow over the board
significantly reduces the junction-to-ambient thermal
resistance. For heatsinking purposes, evenly distribute
the copper area connected at the IC among the high-
current pins.
Power dissipation in the MAX1742/MAX1842 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 = 2.5nF 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
For typical applications, use the recommended compo-
nent values in Tables 1 or 2. For other applications,
take the following steps:
1) Select the desired PWM-mode switching frequency;
__________________Design Procedure
1MHz is a good starting point. See Figure 3 for maxi-
mum operating frequency.
Synchronous Rectification and Internal Switches
T
T
P
PMOS
JA
2
J,MAX
A,MAX
D(TOT)
of copper area and a thermal resistance of
θ
= junction-to-ambient thermal resistance
JA
is the on-resistance of the PMOS switch.
= (T
= maximum junction temperature
= maximum ambient temperature
= total losses
P
P
DS
______________________________________________________________________________________
D
J,MAX
1A/2.7A, 1MHz, Step-Down Regulators with
= I
= C x V
OUT 2
PWM
- T
A,MAX
IN 2
x R
Thermal Resistance
is the switching frequen-
Power Dissipation
x f
PMOS
) / P
PWM
D(T
OT
JA
)
, is highly
Table 1. MAX1742 Recommended
Component Values (I
Table 2. MAX1842 Recommended
Component Values (Continuous Output
Current = 1A, Burst Output Current = 2.7A)
Figure 3. Maximum Recommended Operating Frequency vs.
Input Voltage
V
3.3
3.3
3.3
V
3.3
3.3
3.3
(V)
(V)
5
5
5
5
5
5
5
5
IN
IN
1400
1200
1000
800
600
400
200
V
V
OPERATING FREQUENCY vs. INPUT VOLTAGE
0
(V)
3.3
2.5
1.8
1.5
2.5
1.8
1.5
3.3
2.5
1.8
1.5
2.5
1.8
1.5
(V)
OUT
OUT
2.6
V
OUT
V
OUT
3.1
MAXIMUM RECOMMENDED
= 1.5V
= 1.8V
f
(kHz)
f
(kHz)
1070
1050
1000
1180
PWM
850
910
770
610
PWM
800
850
715
570
985
940
3.6
V
OUT
V
OUT
= 2.5V
IN
4.1
(V)
V
(μH)
(μH)
4.6
= 1A)
5.6
5.6
5.6
5.6
3.9
3.9
3.9
2.2
2.2
2.2
2.2
1.5
1.5
1.5
OUT
L
L
= 3.3V
5.1
5.6
R
R
(kΩ)
(kΩ)
100
100
TOFF
TOFF
39
47
75
39
43
56
39
47
75
39
43
56
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