BD9745EKN Datasheet, PDF (19/22 Pages) Rohm – Silicon Monolithic Integrated Circuit

19/21
５.) Built-in Pch FET(CH1～4,CH67),the drop of current ability in low battery voltage situation
The ON resistance of the built-in Pch FET increase because the FET operates in the saturation region below VGS=1.3V.
Therefore when CH6, 7 step-up converter or step-down channel from a battery is used below 1.8V, the drop is must be considered.
If operating condition below 1.8V should be anticipated, it is recommended that the converter is formed from other channel’s output and is not used
high side switch.
100
100
IDS=200mA
10
10
I_DS=200mA
Recommended region
1
1
Recommended region
0.1
0
1
2
3
4
5
Gate - Source Voltage V_GS[V]
0.1
0
1
2
3
4
5
Gate - Source Voltage V_GS[V]
a. CH４
b. CH７ Highside Switch
Fig - 11 Built-in PMOS ON resistance - V_GS
６.) Setting the oscillator frequency.
The oscillator frequency is user-adjustable by varying the resistor connected to RT (29pin). The CH1～4 frequency is set 1.2MHz to connect 62kΩ,and
the RT value is inverse proportional relation to the frequency.
The CH5～7 frequency is set half value of the CH1～4 frequency.
Fig.12 shows the relation the RT value and the frequency.
10000
CH1～4
1000
CH5～6
100
10
100
1000
RT [kΩ]
Fig -12 Oscillator frequency – RT resister (EX)
REV. D