XC9201 datasheet(13/20 Pages) TOREX

13 / 20 page

2.Oscillation Frequency

The oscillation frequency of the internal clock generator is approximated by the following equation according to the values of the capacitor and

resistor attached to the CLK pin. To stabilize the IC's operation, set the oscillation frequency within a range of 100kHz to 600kHz. Select a

value for Cclk within a range of 180pF to 300pF and fix the frequency based on the value for Rclk.

f=1/ (-Cclk x Rclk x ln 0.26)

Example: When Cclk = 220 pF and Rclk = 10 k

Ω, f = 1/(-220e-12 x 10e3 x ln(0.26)) = 337.43 kHz.

3.Gain and Frequency Characteristics of the Verr Amplifier

The gain at output and frequency characteristics of the Verr amplifier are adjusted by the values of capacitor and resistor attached to the

CC/GAIN pin. It is generally recommended to attach a C_GAIN of 220 to 1,000 pF without an R_GAIN. The greater the C_GAIN value, the

more stable the phase and the slower the transient response. When using the IC with R_GAIN connected, it should be noted that if the R_GAIN

resistance value is too high, abnormal oscillation may occur during transient response time. The size of R_GAIN should be carefully determined

and connected.

4.Current Limiting

The current limiting value is approximated by the following equation according to resistor RSEN inserted between the VIN and ISEN pins. Double

function, current FB input and current limiting, is assigned to the ISEN pin. The current limiting value is approximated by the following equation

according to the value for RSEN.

ILpeak_limit = 0.15 / RSEN

Example: When RSEN = 100 m

Ω, ILpeak_limit = 0.15 / 0.1 = 1.5 A

Because of the feedback at the internal error amp with this IC (which is brought about as a result of the phase compensation of the voltage

generated at RSEN, which is in turn caused by current flowing through the coil when the PMOS is working.), should the value of the RSEN resistor

be too large, the feedback signal will also increase and intermittent oscillation may occur. We therefore recommend that you carefully check the

value for RSEN should you have a problem with oscillation. During normal operations, a voltage will be generated at RSEN as a result of the coil's

peak current. Please ensure that this voltage is less than the current limit voltage which is 90mV (min.).

For RSEN resistor's rated power, please refer to the note on the RSEN resistor on page 18.

XC9201

Series

547

CLK pin

〔Inside the IC〕

Rclk

CLK Generater

Cclk

〔Inside the IC〕

Rsen

VIN pin

Isen pin

Limiter signal

Comparator with

150-mV offset

〔Inside the IC〕

Verr

CC/GAIN pin

RGAIN

VOUT/FB

Vref

RVerr

05S_1XC9201/9202新規 02.09.12 15:16 ページ 547

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