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ILC6377 Datasheet(PDF) 6 Page - Impala Linear Corporation

Part No. ILC6377
Description  0.5A, 300KHZ, SO-8 PWM/PFM STEP DOWN CONVERTER WITH SHUTDOWN
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Maker  IMPALA [Impala Linear Corporation]
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ILC6377 Datasheet(HTML) 6 Page - Impala Linear Corporation

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0.5A, 300kHz, SO-8 PWM/PFM Step Down Converter with Shutdown
Impala Linear Corporation
6
(408) 574-3939
www.impalalinear.com
June 1999
ILC6377 1.3
The EXT1 and EXT2 pins are provided so as to drive
external transistors; thus allowing design flexibility.
The EXT output drive signal has the same timing as
the gate drive to the internal P-channel MOSFET i.e.
EXT output is low as long as the internal MOSFET is
on. Both EXT1 and EXT2 pins are capable of driving
1000pF gate capacitance. For example, a high out-
put current application circuit using an external P-
channel MOSFET is shown in figure 2.
VOUT
ILC6377
(TOP VIE W)
3
45
1
2
6
7
8
+
CL
+
VIN
S/D
CSS
SD1
L
*C
IN
EXT1
Fig.2 1Amp output current application
using external MOSFET
Figure 3. P-Channel Negative
CBST
Voltage between Vin and
ILC6377
(TOP VI EW)
3
4
5
1
2
6
7
8
SD1
2200pF
MA729
Schottky
P-Channel Boost Circuit
The ILC6377 includes a unique P-Channel MOSFET
architecture with built-in charge pump to maintain low
on-resistance even at low input voltages. As shown in
figure 3, a 2200pF ceramic capacitor and a schottky
diode ( MA729 or equivalent ) allows the gate voltage
of the internal P-Channel MOSFET to be driven neg-
ative; thus reducing the switch on-resistance. This
technique can be employed to increase efficiency at
low input voltages and high output currents.
Note that the voltage between VIN and P_BST should not
exceed 10V, otherwise damage to the device may occur.
For high input voltage applications the schottky diode
should be replaced by a low voltage zener diode so that the
P_BST pin is clamped to a safe negative voltage.
VOUT
5
6
CFB
RFB1
RFB2
R
FB 1 + RFB2 ≤ 2MΩ
C
FB chosen s o that 1kHz
1
2
π
×
CF B
×
RFB1
×
-----------------------------------------------------
20kHz
<<
To pin 8
Fig.4 Adjustable output using ILC6377SO-Adj
( Note : rest of circuit is same as Fig.1 )
Adjustable Output ( ILC6377SO-Adj )
For adjustable output voltage ILC6377SO-Adj should be
used. All connections to the ILC6377SO-Adj are the same
as ILC6377SO-XX, except for the feedback voltage divider
network shown in figure 4. The output voltage, VOUT, can be
calculated from the following equation:
VOUT = VFB ( 1 + RFB1/RFB2 ),
where VFB is approximately 1V and
RFB1 + RFB2 < 2M
The feedback compensation capacitor should be chosen
such that the pole frequency f is between 1kHz and 20kHz:
The pole frequency should generally be set at 5kHz. The
value of CFB calculated from the above equation may
require some adjustment depending on the output inductor
( L ) and output capacitor ( CL ) values chosen.
Example for 3V output :
RFB1 = 400k
RFB2 = 200k
CFB = 100pF
PC Board Layout
As with all switching DC-DC converter designs, good PC
board layout is critical for optimum performance. The heavy
lines indicated in figure 1 schematic should be wide
printed circuit board traces and should be kept as short
as is practical. A large ground plane with as much copper
area as is allowable should be used. All external compo-
nents should be mounted as close to the IC as possible. For
ILC6377SO-Adj, the feedback resistors and their associat-
ed wiring should be kept away from the inductor location
and the vicinity of inductive flux.
1
2 x
Π X CFB X RFB1
1kHz<
<20kHz
Fig. 2: 1Amp output current application using external MOSFET
Fig. 3: P-Channel Negative
Fig. 4: Adjustable output using ILC6377SO-Adj
(Note: rest of circuit is same as figure 1)
Voltage between VIN and P_BST
must be less than 10V.


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