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參數(shù)資料
| 型號： | TK652XX |
| 廠商： | TOKO Inc. |
| 英文描述： | STEP-UP VOLTAGE CONVERTER WITH VOLTAGE MONITOR |
| 中文描述： | 升壓電壓電壓監(jiān)控轉(zhuǎn)爐 |
| 文件頁數(shù)： | 16/20頁 |
| 文件大?。?/td> | 141K |
| 代理商： | TK652XX |
ADVANCED INFORMATION
Page 16
January 1999 TOKO, Inc.
TK652xx
HOW TO MAKE A STEP-DOWN CONVERTER USING THE TK652xx AND AN IRF7524D1 “FETKY” PART
The TK652xx can be used as a controller in a step-down converter with the following two additional changes. See Fig 3.
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 TK652xx. 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 V
IN
pin of the TK652xx to below the regulation voltage at the V
OUT
pin.
A resistor
divider between the converter V
IN
and the chip V
IN
pin drops the voltage seen at the V
IN
pin. If the V
IN
pin is a higher voltage
than the VOUT pin, the TK652xx will not regulate the output, but will continue to pulse its output transistor.
WHERE TO USE THIS STEP-DOWN CONVERTER
The TK65221 is a Pulse Burst Modulation (PBM) controller with a fixed duty cycle of approximately 50%. Therefore, only
if V
BATT
is more than twice the voltage of V
OUT
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 V
IN
less than twice the
voltage of V
OUT
. 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.
1 k
+
R3
R4
R1
R2
TKU1
120 μH
C2
47 μF
U2
L1
3
1
4
2
5
VIN
VOUT
GND
SW
IRF7524D1
1,2
4
3
R7
1 k
C1
5,6,
7,8
+
C3
47 μF
6
LOI
R5
R6
VBATT
VOUT
220 pF
LBI
STEP-DOWN CONVERTER APPLICATION
FIGURE 3: STEP-DOWN CONVERTER USING THE TK65221 SCHEMATIC
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
Note: L = 120
μ
H
Toko P/N: 646CY-121M
D75C Coil
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
VOUT Typ. Max IOUT Oper Mode
2.1 V
500 mA
2.1 V
500 mA
2.1 V
500 mA
Inductor
120
μ
H
120
μ
H
120
μ
H
CCM
CCM
CCM
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