TK11830 Ver la hoja de datos (PDF) - Toko America Inc
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TK11830 Datasheet PDF : 13 Pages
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TK11830
APPLICATION INFORMATION
COMPONENT REQUIREMENTS
Inductor
DC resistance of the inductor must be less than 5 Ω. For
optimal performance and efficiency, an inductor with a DC
resistance of less than 1 Ω is recommended. The oscillator
frequency is inversely proportional to inductance. The
inductance should be greater than 300 µH to prevent loss
of efficiency at high frequencies.
There is a large peak current (up to ILPK = 300mA) when
the inductor is saturated.
Control Pin Resistor (RCONT)
Input requirements of the Control pin are as follows:
RCONT
VCONT + ICONT
30 k
VBE
ILPK
L(SMALL)
IL
t
L(LARGE)
CFB, CREF, CIN, COUT
ILPK(MAX)
-300 mA
INDUCTOR
SATURATION
t
When VCONT is high (above 2.2 V), the circuit operation is
stopped. When VCONT is low (below 0.4 V), operation is
resumed.
A control current of 3 µA (typ.) is required for shutdown.
Shutdown voltage, VCONT, is related to the resistance
RCONT as shown below. VCONT changes when RCONT is
changed.
The filtered output ripple is fed back to the feedback pin. To
ensure continuous operation, CFB should be connected
between the feedback pin and ground. If a large voltage is
fed back to the feedback pin, the power transistor switch
drive will be intermittent. This causes a large ripple voltage
since ILPK becomes larger. The value of CFB is determined
by the value of the output capacitor, COUT, and the feedback
resistance, R2. The feedback capacitor must be larger
when the ripple voltage is high due to the lower COUT. CREF
is used to prevent oscillation of the band gap reference and
to stabilize the feedback loop. The input capacitor, CIN, is
used to reduce supply impedance and to provide sufficient
input current during switching for stable circuit operation.
Recommended values:
CREF > 0.1 µF
CFB > 0.01 µF
CIN > 22 µF
COUT > 22 µF
Note: COUT should be sufficiently large and have a low
ESR to minimize ripple voltage.
Page 10
VCONT ~ RCONT x ICONT + VBE
VCONT ~ (300 kΩ) x (3 µA) + 0.7 V = 1.60 V at
RSD = 300 kΩ and VBE ~ 0.7 V
ON/OFF CONTROL
-5
TA = 25 °C
5
-4
4
-3
3
-2
2
-1
1
0
0
0
1
2
VCONT
January 1999 TOKO, Inc.
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