MAX727/MAX728/MAX729
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
Note 1: Do not exceed switch-to-input voltage limitation.
Note 2: For switch currents between 1A and 2A, maximum switch-on voltage can be calculated via linear interpolation.
Note 3: By setting the SENSE pin to 5.5V, the V
C
pin is forced to its low clamp level and the switch duty cycle is forced to zero,
approximating the zero load condition.
Note 4: For proper regulation, total voltage from V
IN
to GND must be ≥ 8V after start-up.
Note 5: To avoid extremely short switch-on times, the switch frequency is internally scaled down when V
SENSE
is less than 2.6V
(MAX727), 2.0V (MAX728), or 1.8V (MAX729). Switch current limit is tested with V
SENSE
adjusted to give a 1µs minimum
switch-on time.
Note 6: Guaranteed, not production tested.
0% duty cycle
0% duty cycle
V
C
Voltage Temperature Coefficient mV/°C
Thermal Resistance Junction to Case
(Note 6)
°C/W4.0
V
-4T
j
= T
MIN
to T
MAX
V
C
Voltage 1.5T
j
= +25°C
Output Voltage Line Regulation %/V0.005 0.0208V ≤ V
IN
≤ 40V
±1.0 ±3.0
T
j
= T
MIN
to
T
MAX
V
OUT
(nominal) = 5V (MAX727),
3.3V (MAX728), or 3V (MAX729);
all conditions of input voltage,
output voltage, and load
current
Output Voltage Tolerance %
±0.5 ±2.0T
j
= +25°C
MAX729
MAX728
MAX727
MAX729
MAX728
MAX727
CONDITIONS
2.2 3.8 6.5
T
j
= +25°CSENSE Pin Divider Resistance 2.5 4.2 7.0 kΩ
3.0 5.0 8.0
2.90 3.00 3.10
V
C
= 2VSENSE Voltage
3.20 3.30 3.40
V
4.85 5.00 5.15
UNITSMIN TYP MAXPARAMETER
______________________________________________________________Pin Description
5
V
IN
supplies power to the internal circuitry and also connects to the collector of the internal power
switch. V
IN
must be bypassed with a low-ESR capacitor, typically 200µF or 220µF.
Internal Power Switch Output. The Switch output can swing 35V below ground and is rated for 2A.
Ground requires a short, low-noise connection to ensure good load regulation. The internal refer-
ence is referred to GND, so errors at this pin are multiplied by the error amplifier.
Error-Amplifier Output. A series RC network connected to this pin compensates the
MAX727/MAX728/MAX729. Output swing is limited to about 5.8V in the positive direction and
-0.7V in the negative direction. V
C
can also synchronize the MAX727/MAX728/MAX729 to an
external TTL clock in the 115kHz to 170kHz range. See MAX724/MAX726 data sheet.
SENSE Input is the internal error amplifier's input, and should be directly connected to V
OUT
.
SENSE also aids current limiting by reducing oscillator frequency when V
OUT
is low.
4
3
2
1
PIN
V
IN
V
SW
GND
V
C
SENSE
FUNCTIONNAME
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