TK65127MTL データシートの表示（PDF） - Toko America Inc
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TK65127MTL Datasheet PDF : 20 Pages
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TK651xx
STEP-DOWN CONVERTER APPLICATION
HOW TO MAKE A STEP-DOWN CONVERTER USING THE TK651xx AND AN IRF7524D1 “FETKY” PART
The TK651xx can be used as a controller in a step-down converter with the following two additional changes. See Fig 3.
VBATT
U2
IRF7524D1
3
R3
1k
4
5,6,
7,8
1,2
R4
U1
150
R1 TK65130
10 k
SW
3
GND
2
1 VOUT 4
R5
300 k
R2
3.9 k
VIN
LOI 6
5
GND
R6
300 k
L1
10 µH
R7
1k
C1
220 pF
VOUT
+
+
C2
C3
47 µF 47 µF
Note: L = 10 µH
Toko P/N: 636CY-100M
D73C Coil
FIGURE 3: STEP-DOWN CONVERTER USING THE TK651xx SCHEMATIC
1) Change the main switch orientation for use in a step-down converter. An external P-channel power MOSFET is
used as the main switch in a step-down converter configuration. The gate of FET is turned on through a resistor divider
being pulled down to GND by the internal output transistor of the TK651xx. This application requires both a logic level
P-channel MOSFET and a Schottky diode. An IRF7524D1 “FETKY” part contains both in a small micro 8 package.
2) Change the voltage seen at the VIN pin of the TK651xx to below the regulation voltage at the VOUT pin. A resistor
divider between the converter VIN and the chip VIN pin drops the voltage seen at the VIN pin. If the VIN pin is a higher voltage
than the VOUT pin, the TK651xx will not regulate the output, but will continue to pulse its output transistor.
WHERE TO USE THIS STEP-DOWN CONVERTER
The TK65130 is a Pulse Burst Modulation (PBM) controller with a fixed duty cycle of approximately 50%. Therefore, only
if VBATT is more than twice the voltage of VOUT can the converter run in CCM (continuous current mode). The converter
can and does regulate in DCM (discontinuous current mode) for lighter output current loads with VIN less than twice the
voltage of VOUT. But DCM produces more peak current and more ripple current than CCM. Below is a table giving some
examples of where this type of step-down converter might be used.
Type Battery
Li-ion
NiMH
NiMH
# of Cells
2 (Note 1)
4 (Note 2)
6 (Note 2)
VBATT Range
5.4 to 8.4 V
4.4 to 5.2 V
6.6 to 7.8 V
Note 1: Li-ion cell voltage range 2.7 V to 4.2 V
Note 2: NiMH cell voltage range 1.1 V to 1.3 V
VOUT
3.0 V
3.0 V
3.0 V
Typ. Max. IOUT
500 mA
500 mA
500 mA
Oper. Mode
DCM
DCM
CCM
Inductor
10 µH
10 µH
120 µH
January 1999 TOKO, Inc.
Page 17
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