MAX773ESD+ Maxim Integrated Products, MAX773ESD+ Datasheet - Page 12

• Manufacturer Part Number: MAX773ESD+
• Description: IC CNTRLR DC-DC 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX773ESD+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V, 12V, 15V, Adj
• Current - Output: 1A
• Frequency - Switching: 300kHz
• Voltage - Input: 3 ~ 16.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Power - Output: 667mW
• Output Voltage: 5 V, 12 V, 15 V, 3 V
• Output Current: 1 A
• Input Voltage: 3 V to 16.5 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

turned on, it stays on until either 1) the maximum on-
time one-shot turns it off (typically 16µs later), or 2) the
switch current reaches the peak current limit set by the
current-sense resistor.
To increase light-load efficiency, the current limit for the
first two pulses is set to one-half the peak current limit.
If those pulses bring the output voltage into regulation,
the error comparator holds the MOSFET off and the
current limit remains at one-half the peak current limit. If
the output voltage is still out of regulation after two
pulses, the current limit for the next pulse is raised to
the peak current limit set by the external sense resistor
(see inductor current waveforms in the Typical
Operating Characteristics ).
The MAX770–MAX773 switching frequency is variable
(depending on load current and input voltage), causing
variable switching noise. However, the subharmonic
noise generated does not exceed the peak current limit
times the filter capacitor equivalent series resistance
(ESR). For example, when generating a 12V output at
500mA from a 5V input, only 180mV of output ripple
occurs using the circuit of Figure 2b.
5V/12V/15V or Adjustable, High-Efficiency,
Low I
Figure 3e. 100V Output, Shunt Regulator, N-Channel Power
MOSFET
12
0.1 F
V
IN
C2
= 24V TO 28V
C3
0.1 F
______________________________________________________________________________________
10
47 F
4
8
5
7
C1
SGND
REF
LBI
SHDN
LBO
Q
MAX773
, Step-Up DC-DC Controllers
GND
v+
9
3
R
3k
SHUNT
EXTH 13
EXTL
V15
V12
CS
V5
FB
11
1
2
6
12
14
11.3k (1%)
250 H
L1
R1
N
Si9420DY
732k (1%)
MUR115
R
1.0
SENSE
D1
R2
R2 = (R1)
V
REF
= 1.5V
C4
100 F
(
V
V
OUT
V
@ 10mA
OUT
REF
= 100V
-1
)
The MAX770/MAX771/MAX772 feature a low input volt-
age start-up oscillator that guarantees start-up with no
load down to 2V when operating in bootstrapped mode
and using internal feedback resistors. At these low volt-
ages, the supply voltage is not large enough for proper
error-comparator operation and internal biasing. The
start-up oscillator has a fixed 50% duty cycle and the
MAX770/MAX771/MAX772 disregard the error-com-
parator output when the supply voltage is less than
2.5V. Above 2.5V, the error-comparator and normal one-
shot timing circuitry are used. The low voltage start-up
circuitry is disabled if non-bootstrapped mode is select-
ed (FB is not tied to ground).
The MAX773 does not provide the low-voltage 50%
duty-cycle oscillator. Its minimum start-up voltage is 3V
for all modes.
An N-FET power switch is recommended for the
MAX770/MAX771/MAX772.
The MAX773 can drive either an N-channel MOSFET
(N-FET) or an NPN because it provides two separate
Figure 4. MAX773 Shunt Regulator
V
R
*
IN
SHUNT =
SEE TEXT FOR I
R
SHUNT
0.1 F
C2
V
IN (MIN)
SHUNT
I
- V
SHUNT
Low-Voltage Start-Up Oscillator
SHUNT
CALCULATION
3
*
V+
(
MAX
)
External Transistor
6V (typ)
MAX773
10
SGND