MAX1642EVKIT Maxim Integrated, MAX1642EVKIT Datasheet - Page 2

• Manufacturer Part Number: MAX1642EVKIT
• Description: Power Management IC Development Tools
• Manufacturer: Maxim Integrated
• Series: MAX1642, MAX1643r

MAX1642 EV Kit
MAX1642 Evaluation Kit
_______________Detailed Description
The MAX1642 EV kit provides a 3.3V output from a 0.9V
to 1.65V input voltage. It delivers up to 20mA with 80%
typical conversion efficiency.
The 3-pin header JU1 selects shutdown mode. Table 1
lists the selectable jumper options. In shutdown, the
internal switching MOSFET turns off,
high-impedance state, and the synchronous rectifier
turns off to prevent reverse current from flowing
through the output back to the input. However, there is
still a forward current path through the synchronous-
rectifier body diode from the input to the output. Thus,
the output doesn’t drop lower than a diode drop below
the battery voltage. Connect the SHDN pin to VIN for
normal operation.
The MAX1642 is preset for a 3.3V output voltage.
However, its output can be adjusted via an external volt-
age divider formed by R1 and R2 (located on the bottom
of the board). The only other modification required is to
cut the trace across R2. Since FB leakage is 10nA max,
select feedback resistor R2 in the 100k
R1 is given by the following equation:
2
Table 1. Jumper JU1 Functions
where V
LOCATION
_______________________________________________________________________________________
8/7/97 5:05 PM
SHUNT
1 and 2
2 and 3
REF
= 1.23V (the internal reference voltage).
Evaluating Other Output Voltages
R
1
Connected to GND
Connected to VIN
Page 2
S S H H D D N N PIN
R
2
V
V
OUT
REF
Jumper Selection
- 1
MAX1642 OUTPUT
MAX1642 enabled,
V
Shutdown mode,
V
OUT
OUT
PFO goes into a
to 1M
= V
= 3.3V
IN
- V
DIODE
range.
The MAX1642 has an on-chip comparator for power-fail
detection. This comparator can be used to detect loss of
power at the input or output. The MAX1642 EV kit
detects power loss at the input. If the voltage at PFI falls
below 614mV ±3%, the PFO output sinks current
to GND.
The power-fail monitor’s threshold is set by two resistors:
R3 and R4. Refer to the Power-Fail Detection section in
the MAX1642 data sheet for instructions on selecting
resistors R3 and R4.
The MAX1642 EV kit can also be used to evaluate the
MAX1643. The only modifications required are to replace
the MAX1642 with the MAX1643 and remove the shunt
from JU1. Refer to the Detailed Description and Pin
Description sections of the data sheets for the differ-
ences between the MAX1642 and MAX1643.
Evaluating the MAX1643
Power-Fail Output