2003 Microchip Technology Inc.
DS51315A-page 5
MCP1601 Evaluation Board
1.2.4
Selecting the Operating Mode - Using Switch U3, Position 2
The multi-function SYNC/PWM pin on the MCP1601 is used to set the operating mode
of the device. The three operating modes are:
• Automatic switching from PFM Mode to PWM mode and back
• Synchronization to external Oscillator
• Fixed Frequency Forced PWM Mode
To select automatic PFM/PWM mode:
• Slide switch U
3
, position 2 to the left or off position. While operating in this mode,
the MCP1601 device will automatically select the most efficient operating mode
by approximating the load current internally.
To synchronize the MCP1601 switching frequency to an external oscillator:
• Slide switch U
3
, position 2 to the left. Connect the external oscillator to the
SYNC/PWM test point located directly below switch U
3
and the A
GND
test point.
See the MCP1601 datasheet (DS21762) for external clock specifications. When
synchronizing to an external oscillator, the MCP1601 will operate in the fixed
frequency mode at the same frequency as the external oscillator.
To select fixed frequency mode that operates off of the 750 kHz internal oscillator:
• Slide switch U
3
, position 2 to the right or “on” position. This will tie the SYNC/PWM
pin high and force PWM operation from the internal oscillator, making the
MCP1601 device independent of external load conditions.
1.2.5
Selecting the MCP1601 output voltage
Switch U
2
is used to select the output voltage. Refer to Table 1-1 to choose one of the
pre-selected output voltages.
TABLE 1-1:
SWITCH SETTINGS FOR PRE-SELECTED OUTPUT
VOLTAGES
The output voltage for the MCP1601 device is determined by using the following for-
mula.
EQUATION
U2, Position 1 U2, Position 2
V
OUT
OFF
OFF
3.28V
OFF
ON
2.45V
ON
OFF
2.05V
ON
ON
1.8
Where: V
REF
= 0.8V Typical
R
4
= 200 k
Ω
for the Evaluation board
R
2
is set by the parallel combination of R
1
, R
2
and R
3
.
V
OUT
V
REF
1
R
2
R
4
-------
+
=
