ARM IM-AD1 - Manual (Page 62)

Reference Design Example
4-16 Copyright © 2001-2003. All rights reserved. ARM DUI 0163B
4.6 PWM controller
The PWM control function is implemented by the DC-DC converter PrimeCell
(PL160). Refer to the ARM PrimeCell DC-DC Converter Interface (PL160) Technical
Reference Manual for information about this device.
The DC-DC PrimeCell uses the 4MHz IM_CLK signal to supply the DCDCCLK
reference clock. It can divide this by 16, 32, 128, or 304 to provide four possible
switching frequencies of 250kHz, 125kHz, 31.25kHz, and 13.158kHz.
The switching circuitry has turn on and turn off delays that limit the minimum pulse
width and can also affect the accuracy of the PWM, particularly at the higher switching
frequencies between 125kHz to 250kHz. The turn on and turn off delays for different
voltages are shown in Table 4-9.
Table 4-9 PWM turn on and turn off delays
Load voltage Turn on time Turn off time
5V 1
μs
0.6
μs
30V 2
μs
1.2
μs