EL7512C 데이터 시트보기 (PDF) - Elantec -> Intersil
부품명
상세내역
제조사
EL7512C Datasheet PDF : 9 Pages
| |||
EL7512C - Preliminary
High Frequency PWM Step-Up Regulator
Applications Information
The EL7512C is a step-up regulator, operated at fixed
frequency pulse-width-modulation (PWM) control. The
input voltage is 2V-12V and output voltage is 5V-16V.
The switching frequency (up to 1.2MHz) is decided by
the resistor connected to RT pin.
Start-up
After VDD reaches a threshold of about than 2V, the
power MOSFET is controlled by the start-up oscillator,
which generates fixed duty-ratio of 0.5-0.7 at a fre-
quency of several hundred kilohertz. This will boost the
output voltage.
When VDD reaches about 3.7V, the PWM comparator
takes over the control. The duty ratio will be decided by
the multiple-input direct summing comparator,
Max_Duty signal (about 90% duty-ratio), and the Cur-
rent Limit Comparator, whichever is the smallest.
The soft-start is provided by the current limit compari-
tor. As the internal 12µA current source changes the
external CSS, the peak MOSFET current is limited by
the voltage on the capacitor. This in turn controls the ris-
ing rate of output voltage.
The regulator goes through the start-up sequence as well
after the EN signal is pulled to HI.
Steady-State Operation
When the output reaches the preset voltage, the regulator
operates at steady state. Depending on the input/output
condition and component, the inductor operates at either
continuous-conduction mode or discontinuous-conduc-
tion mode.
In the continuous-conduction mode, the inductor current
is a triangular waveform and LX voltage a pulse wave-
form. In the discontinuous-conduction mode, the
inductor current is complete dry out before the MOSFET
is turned on again. The input voltage source, the induc-
tor, and the MOSFET and output diode parasitic
capacitors forms a resonant circuit. Oscillation will
occur in this period. This oscillation is normal and will
not affect the regulation.
At very low load, the MOSFET will skip pulse some-
times. This is normal.
Current Limit
The MOSFET current limit is nominal 1.2A and guaran-
teed 1A. This restricts the maximum output current
Iomax based on the following formula:
IOMAX = 1 – ∆----2-I--L-- × V--V---I-O-N---
where:
∆IL is the inductor peak-to-peak current ripple and is
decided by:
∆IL = V----L-I---N-- × F--D--S--
D is the MOSFET turn-on radio and is decided by:
D = V-----O----V--–---O-V-----I--N--
FS is the switching frequency.
The following table gives typical values:
Maximum Output Current
VIN (V)
2
2
2
3
3
3
4.5
4.5
4.5
9
9
VO (V)
5
9
12
5
9
12
9
12
15
12
15
L (µH)
10
10
10
10
10
10
10
10
10
10
10
FS (kHz)
600
600
600
600
600
600
600
600
600
600
600
IOMAX (mA)
360
190
140
540
270
200
400
280
220
600
420
Component Considerations
It is recommended that CIN is larger than 10µF. Theoret-
ically, the input capacitor has ripple current of ∆IL. Due
to high-frequency noise in the circuit, the input current
ripple may exceed the theoretical value. Larger capacitor
will reduce the ripple further.
6
Share Link: 