BD9011EKN View Datasheet(PDF) - ROHM Semiconductor

Part Name

Description

Manufacturer

BD9011EKN

Dual-output, high voltage, high-efficiency step-down Switching Regulator (Controller type)

ROHM Semiconductor 

(7) Setting over current detection values

The current limit value（ILimit）is determined by the resistance of the RCL established between CL and VCCCL.

VIN

VCCCL

IL

RCL

CL

IL

Vo

L

Over current detection point

90m

ILimit =

[A]・・・(13)

RCL

Fig-23

Fig-24

There are 2 current limit function (ON/OFF control type and OFF latch type) toggled by LOFF pin.

・LOFF=L (0<LOFF<1V): Off Latch Type Current Limit

The output becomes OFF and latched when SS=H and, current limit operation, and the output voltage is less than or equal

to 70% of Vo. The OFF latch is deactivated by re-inputting EN signal or VCC control input (switch OFF and ON once more).

・LOFF=H (1<LOFF<VREG5): ON/OFF Control Type Current Limit

When the current goes beyond the threshold value, the current can be limited by reducing the ON Duty Cycle. When the load

goes back to the normal operation, the output voltage also becomes back on to the specific level.

The current limit value

Vo

LOFF=L

（OFF Latch）

Vo×70%

LOFF=H

Fig-25

Io

(8) Method for determining phase compensation

Conditions for application stability

Feedback stability conditions are as follows:

・When gain is 1 (0dB) and phase shift is 150° or less (i.e., phase margin is at least 30°):

a dual-output high-frequency step-down switching regulator is required

Additionally, in DC/DC applications, sampling is based on the switching frequency; therefore, overall GBW may be set at no

more than 1/10 the switching frequency. In summary, target characteristics for application stability are:

・Phase shift of 150° or less (i.e., phase margin of 30° or more) with gain of 1 (0dB)

・GBW (i.e., gain 0dB frequency) no more than 1/10 the switching frequency.

Stability conditions mandate a relatively higher switching frequency, in order to limit GBW enough to increase response.

The key to achieving successful stabilization using phase compensation is to cancel the secondary phase margin/delay

(-180°) generated by LC resonance, by employing a dual phase lead. In short, adding two phase leads stabilizes the

application.

GBW (the frequency at gain 1) is determined by the phase compensation capacitor connected to the error amp. Thus, a larger

capacitor will serve to lower GBW if desired.

① General use integrator (low-pass filter) ② Integrator open loop characteristics

Feedback R

A

FB

C

Fig-26

COMP

A 1 8 0

Gain

[dB] 9 0

0

Phase 00

[deg] --9900

-1- 188 00

(a) -20dB/decade

GBW(b)

-90°

Phase margin

-180°

1

point (a) fa = 2πRCA 1.25[Hz]

1

point (b)点 fa = GBW 2πRC [Hz]

Fig-27

The error amp is provided with phase compensation similar to that depicted in figures ① and ② above and thus serves

as the system’s low-pass filter.

In DC/DC converter applications, R is established parallel to the feedback resistance.

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