參數(shù)資料
型號(hào): PM6686
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, QCC32
封裝: 5 X 5 MM, 1 MM HEIGHT, 0.50 MM PITCH, ROHS COMPLIANT, VFQFPN-32
文件頁數(shù): 19/50頁
文件大?。?/td> 1066K
代理商: PM6686
Device description
PM6686
26/50
Doc ID 15281 Rev 4
8.1.2
Constant on time control (COT)
PM6686 implements a pseudo-fixed frequency algorithm using the COT architecture. The
two sections are completely independent with separated switching controllers (SMPS).
The COT architecture bases its algorithm on the output ripple derived across the output
capacitor's ESR. The controller has an internal on time (TON) generator triggered on the
output voltage valley: when VOUT reaches the regulation value a new TON starts. The TON
duration is given by the following equation:
Equation 2
Where TON is the on time duration, K is a constant, VOUT is the sensed output voltage and
VIN is the input voltage.
The duty cycle in a buck converter is:
Equation 3
The switching frequency in continuous current mode (CCM) is:
Equation 4
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 the switching frequencies that can be selected through TON pin:
Table 8.
Frequency configurations
TON
SMPS 1
SMPS 2
Frequency
K
Frequency
K
VCC
200 kHz
5 s
300 kHz
3.33 s
VREF2 or open
400 kHz
2.5 s
300 kHz
3.33 s
GND
400 kHz
2.5 s
500 kHz
2 s
IN
OUT
ON
V
K
T
=
IN
OUT
SW
ON
V
D
T
=
K
1
V
K
V
T
D
f
IN
OUT
IN
OUT
ON
SW
=
=
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