Datasheet

Device description PM6644
16/35 Doc ID 023203 Rev 1
Equation 5
The switching frequency is theoretically constant, but in a real application it depends on
parasitic voltage drops that occur during the charging path (high-side switch resistance,
inductor resistance (DCR)) and discharging path (low-side switch resistance, DCR). As a
result, the switching frequency increases as a function of the load current. The following
table shows some examples of switching frequencies that can be selected through the TON
pin (C
1
not mounted):
2.1.3 PWM control
Figure 20 shows the simplified schematic of the constant-on-time controller. The COT
architecture uses a minimum OFF-time (T
OFFMIN
= 500 ns typ.) to allow inductor valley
current sensing on the synchronous switch. A minimum on-time is also introduced to assure
the correct startup sequence.
An adaptive anti-cross conduction algorithm avoids current paths between VIN and GND
during switching transition.
Table 7. Frequency configurations
T
ON
resistor
R_T
ON
V
OUT
= 3.47 V frequency
load = 200 mA (PWM mode)
V
OUT
= 0. 9 V frequency
load = 200 mA (PWM mode)
2 M 245 kHz
1 M 470 kHz
500 K 260 kHz
250 K 495 kHz
f
sw
D
T
ON
-----------
V
OUT
V
IN
0.9V R
TON
CC
1
+()⋅⋅
V
IN
-----------------------------------------------------------------
-----------------------------------------------------------------
-----------------------------------------------------------------
V
OUT
0.9V R
TON
CC
1
+()⋅⋅
-----------------------------------------------------------------===