EL7535 INTERSIL [Intersil Corporation], EL7535 Datasheet - Page 6

• Manufacturer Part Number: EL7535
• Description: Monolithic 350mA Step-Down Regulator
• Manufacturer: INTERSIL [Intersil Corporation]

Waveforms
All waveforms are taken at V
Applications Information
Product Description
The EL7535 is a synchronous, integrated FET 350mA step-
down regulator which operates from an input of 2.5V to 6V.
The output voltage is user-adjustable with a pair of external
resistors.
The internally-compensated controller makes it possible to
use only two ceramic capacitors and one inductor to form a
complete, very small footprint 350mA DC/DC converter.
PWM Operation
In the PWM mode, the P channel MOSFET and N channel
MOSFET always operate complementary. When the
PMOSFET is on and the NMOSFET off, the inductor current
increases linearly. The input energy is transferred to the
output and also stored in the inductor. When the P channel
MOSFET is off and the N channel MOSFET on, the inductor
FIGURE 7. POR FUNCTION
(Continued)
IN
50ms/DIV
=3.3V, V
6
O
=1.8V, I
∆V
∆V
V
LX
IN
i
O
O
L
=350mA with component values shown on page 1, unless otherwise noted
RSI
(2V/DIV)
V
(2V/DIV)
V
(2V/DIV)
POR
(2V/DIV)
IN
O
FIGURE 9. STEADY-STATE
EL7535
1µs/DIV
current decreases linearly, and energy is transferred from
the inductor to the output. Hence, the average current
through the inductor is the output current. Since the inductor
and the output capacitor act as a low pass filter, the duty
cycle ratio is approximately equal to V
The output LC filter has a second order effect. To maintain
the stability of the converter, the overall controller must be
compensated. This is done with the fixed internally
compensated error amplifier and the PWM compensator.
Because the compensations are fixed, the values of input
and output capacitors are 10µF to 22µF ceramic. The
inductor is nominally 1.8µH, though 1.5µA to 2.2µH can be
used.
Start-Up and Shut-Down
When the EN pin is tied to V
approximately 2.4V, the regulator begins to switch. The
∆V
I
O
O
FIGURE 8. TRANSIENT RESPONSE
0.5A/DIV
2V/DIV
10mV/DIV
100mV/DIV
0.2ms/DIV
IN
, and V
IN
O
reaches
divided by V
August 16, 2005
350mA
100mA
20mV/DIV
IN
FN7003.2
.