MAX771ESA+ Maxim Integrated Products, MAX771ESA+ Datasheet - Page 14

• 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

Table 1. Bootstrapped vs. Non-Bootstrapped Operation
Use an N-channel FET as the power switch when using
the shunt regulator (see MAX773 Shunt-Regulator
Operation in the Detailed Description ). The shunt-regu-
lator current powers the MAX773 and also provides the
FET gate-drive current, which depends largely on the
FET’s total gate charge at V
shunt-resistor value, first determine the maximum shunt
current required.
See N-Channel MOSFETs in the Power-Transistor
Selection section to determine I
Determine the shunt-resistor value using the following
equation:
where V
The shunt regulator is not disabled in shutdown
mode, and continues to draw the calculated shunt
current.
If the calculated shunt regulator current exceeds 20mA,
or if the shunt current exceeds 5mA and less shunt reg-
ulator current is desired, use the circuit of Figure 6 to
provide increased drive and reduced shunt current
when driving N-FETs with large gate capacitances.
Select I
current for this circuit, although higher shunt currents
can be used.
5V/12V/15V or Adjustable, High-Efficiency,
Low I
*MAX773(S) indicates shunt mode; MAX773(N) indicates NOT in shunt mode.
14
Gate Drive
FET On Resistance
Gate-Drive Capacitive Losses
No-Load Supply Current
Possible Input Voltage Range
Normally Recommended Input
Voltage Range
Fixed Output Available
Adjustable Output Available
______________________________________________________________________________________
R
SHUNT
SHUNT
SHUNT
Q
PARAMETER
(max) = ————————————
(max) is 6.3V.
= 3mA. This provides adequate biasing
I
, Step-Up DC-DC Controllers
SHUNT
= I
V
IN
SUPP
(min) - V
GS
GATE
= 5V. To determine the
+ I
I
SHUNT
GATE
SHUNT
.
GND to V
Lower
Higher
Higher
2V to 16.5V (MAX770/MAX771/MAX772),
(internal feedback resistors)
3V to 16.5V (MAX770/MAX771/MAX772),
(external feedback resistors)
3V to 16.5V (MAX773)
2V to 5V (MAX770/MAX771/MAX772),
3V to 5V (MAX773)
MAX770–MAX773(N)
MAX770–MAX773(N)
(max)
OUT
BOOTSTRAPPED*
To prevent the shunt regulator from drawing current in
shutdown mode, place a switch in series with the shunt
resistor.
Figure 6. Increased N-FET Gate Drive when Using the Shunt
Regulator
R
MAX773
SHUNT
V
V+
IN
3
SGND
EXTL
EXTH
0.1 F
C2
CS
FB
10
13
12
11
6
C1
100
GND to V+
Higher
Lower
Lower
3V to 16.5V
(MAX770/MAX771/MAX772),
3V and up (MAX773)
5V to 16.5V
(MAX770/MAX771/MAX772),
5V and up (MAX773)
MAX773(N)/MAX773(S)
MAX770/MAX771/MAX772/
MAX773(N)/MAX773(S)
NON-BOOTSTRAPPED
NPN
2N2222A
PNP
2N2907A
R
SENSE
N
L1
20 H
D1
R2
R1
V
C4
OUT