MAX771ESA+ Maxim Integrated Products, MAX771ESA+ Datasheet - Page 18

• 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

Smaller capacitors are acceptable for light loads or in
applications that can tolerate higher output ripple.
Since the output filter capacitor’s ESR affects efficien-
cy, use low-ESR capacitors for best performance. The
smallest low-ESR surface-mount tantalum capacitors
currently available are the Sprague 595D series. Sanyo
OS-CON organic semiconductor through-hole capaci-
tors and the Nichicon PL series also exhibit low ESR.
See Table 2.
The input bypass capacitor (C1) reduces peak currents
drawn from the voltage source and also reduces noise
at the voltage source caused by the switching action of
the MAX770–MAX773. The input voltage source imped-
ance determines the size of the capacitor required at
the V+ input. As with the output filter capacitor, a low-
ESR capacitor is recommended. For output currents up
to 1A, 150µF (C1) is adequate, although smaller
bypass capacitors may also be acceptable.
Bypass the IC with a 0.1µF ceramic capacitor (C2)
placed close to the V+ and GND pins.
Bypass REF with a 0.1µF capacitor (C3). REF can
source up to 100µA of current.
To set the low-battery detector’s falling trip voltage
(V
(Figure 9), and calculate R4 as follows:
where V
The rising trip voltage is higher because of the com-
parator’s approximately 20mV of hysteresis, and is
determined by:
Connect a high value resistor (larger than R3 + R4)
between LBI and LBO if additional hysteresis is required.
Connect a pull-up resistor (e.g., 100k ) between LBO
and V+. Tie LBI to GND and leave LBO floating if the
low-battery detector is not used.
5V/12V/15V or Adjustable, High-Efficiency,
Low I
18
Setting the Low-Battery-Detector Voltage
TRIP
______________________________________________________________________________________
(falling)), select R3 between 10k
V
REF
TRIP
= 1.5V.
Q
(rising) = (V
R4 = (R3)
, Step-Up DC-DC Controllers
(
REF
———————
V
TRIP
+ 20mV) (1 + ——)
Input Bypass Capacitors
V
REF
- V
Reference Capacitor
REF
)
R4
R3
and 500k
The MAX773’s shunt regulator input allows high volt-
ages to be converted to very high voltages. Since the
MAX773 runs off the 6V shunt (bootstrapped operation
is not allowed), the IC will not see the high input volt-
age. Use an external logic-level N-FET as the power
switch, since only 6V of V
sure all external components are rated for very high
output voltage. Figure 3e shows a circuit that converts
28V to 100V.
When using a power supply that decays with time
(such as a battery), the N-FET transistor will operate in
its linear region when the voltage at EXT approaches
the threshold voltage of the FET, dissipating excessive
power. Prolonged operation in this mode may damage
the FET. This effect is much more significant in non-
bootstrapped mode than in bootstrapped mode, since
bootstrapped mode typically provides much higher
V
is above the V
(such as the MAX8211) to put the IC in shutdown mode
once the input supply voltage falls below a predeter-
mined minimum value. Excessive loads with low input
voltages can also cause this condition.
Figure 9. Input Voltage Monitor Circuit
__________Applications Information
GS
voltages. To avoid this condition, make sure V
R4 = R3
V
REF
TH
R4
R3
= 1.5V
(
of the FET, or use a voltage detector
MAX773 Operation with High
Low Input Voltage Operation
V
V
TRIP
REF
LBI
-1
)
MAX773
GND
GS
V+
Input/Output Voltages
V
IN
are available. Also, make
LBO
LOW-BATTERY
OUTPUT
R5
100k
EXT