MAX771ESA+ Maxim Integrated Products, MAX771ESA+ Datasheet - Page 15

• Manufacturer Part Number: MAX771ESA+
• Description: IC CNTRLR DC-DC 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX771ESA+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 12V, Adj
• Current - Output: 1A
• Frequency - Switching: 300kHz
• Voltage - Input: 2 ~ 16.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 471mW
• Output Voltage: 12 V or 3 V (Min)
• Output Current: 1 A (Max)
• Input Voltage: 2 V to 16.5 V
• Supply Current: 110 uA
• Switching Frequency: 300 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 7a. Maximum Output Current vs. Input Voltage
(V
Figure 7c. Maximum Output Current vs. Input Voltage
(V
The Typical Operating Characteristics graphs show the
output current capability for various modes, sense
resistors, and input/output voltages. Use these graphs,
along with the theoretical output current curves shown
in Figures 7a-7d, to select R
curves assume that an external N-FET power switch is
used. They were derived using the minimum (worst-
case) current-limit comparator threshold value, and the
inductance value. No tolerance was included for
R
assumed to be 0.5V, and the drop across the power
switch r
0.3V. To use the graphs, locate the graph with the
appropriate output voltage or the graph having the
nearest output voltage higher than the desired output
voltage. On this graph, find the curve for the largest
SENSE
OUT
OUT
= 5V)
= 15V)
DS(ON)
. The voltage drop across the diode was
3.5
3.0
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2
2
R
V
L = 22 H
R
V
L = 22 H
and coil resistance was assumed to be
SENSE
OUT
SENSE
5V/12V/15V or Adjustable, High-Efficiency,
OUT
R
R
______________________________________________________________________________________
SENSE
SENSE
4
= 15V
= 5V
R
= 50m
= 75m
SENSE
= 40m
= 50m
6
= 40m
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3
8
Determining R
SENSE
10
R
R
SENSE
R
SENSE
SENSE
R
4
R
SENSE
SENSE
12
= 200m
= 75m
. These theoretical
= 100m
Low I
= 200m
= 100m
14
16
5
SENSE
Q
, Step-Up DC-DC Controllers
sense-resistor value with an output current that is ade-
quate at the lowest input voltage.
Practical inductor values range from 10µH to 300µH.
20µH is a good choice for most applications. In appli-
cations with large input/output differentials, the IC’s
output current capability will be much less when the
inductance value is too low, because the IC will always
operate in discontinuous mode. If the inductor value
is too low, the current will ramp up to a high level
before the current-limit comparator can turn off the
switch. The minimum on-time for the switch (t
is approximately 2µs; select an inductor that allows
the current to ramp up to I
Choosing a value of I
pulses to occur, increasing light-load efficiency and
minimizing output ripple.
Figure 7b. Maximum Output Current vs. Input Voltage
(V
Figure 7d. Maximum Output Current vs. Input Voltage
(V
OUT
OUT
= 12V)
= 24V)
0.8
0.6
0.4
0.2
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2
2
V
L =150 H
L = 22 H
R
V
R
OUT
SENSE
OUT
SENSE
R
Determining the Inductor (L)
= 24V
SENSE
= 12V
R
= 75m
SENSE
4
= 100m
LIM
= 50m
6
= 40m
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
/2 allows the half-size current
6
LIM
10
/2 in no less than 2µs.
8
R
R
R
SENSE
R
SENSE
SENSE
SENSE
= 200m
= 200m
= 400m
= 100m
10
14
12
ON
(min))
15