Rainbow Electronics MAX652 - Manual (Page 6)

MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q , Step-Down DC-DC Controllers
6 _______________________________________________________________________________________
MAX649
LINE-TRANSIENT RESPONSE
250 µ s/div
A
B
I LOAD = 1A
A: INPUT VOLTAGE (7V & 12V), 5V/div
B: 5V OUT, AC COUPLED, 100mV/div
_____________________________Typical Operating Characteristics (continued)
MAX649
LOAD-TRANSIENT RESPONSE
250 µ s/div
A
B
A: LOAD CURRENT (100mA & 1A), 500mA/div
B: 5V OUTPUT VOLTAGE, AC COUPLED, 50mV/div
______________________________________________________________Pin Description
Positive power-supply input V+ 5
CS 6
Gate drive for external P-channel MOSFET. EXT swings between V+ and GND. EXT 7
Ground GND 8
1.5V reference output that can source 100µA. Bypass with 0.1µF. REF 4
SHDN 3
PIN
FB 2
OUT 1
FUNCTION NAME
Sense input for fixed 5V, 3.3V, or 3V output operation. OUT is internally connected to the on-chip voltage divider.
Although it is connected to the output of the circuit, the OUT pin does not supply current.
Feedback input. Connect to GND for fixed-output operation. Connect a resistor divider between OUT, FB,
and GND for adjustable-output operation. See
Setting the Output Voltage section.
Active-high TTL/CMOS logic-level input. Part is placed in shutdown when SHDN is driven high. In shutdown mode,
the reference and the external MOSFET are turned off, and OUT = 0V. Connect to GND for normal operation.
Current-sense input. Connect current-sense resistor between V+ and CS. When the voltage across the
resistor equals the current-limit trip level, the external MOSFET is turned off.
MAX649
SHUTDOWN RESPONSE TIME
1ms/div
A
B
I LOAD = 1A
A: SHDN INPUT VOLTAGE (0V & 5V), 2V/div
B: 5V OUTPUT VOLTAGE, 2V/div