AAT1236 Analogic Corporation, AAT1236 Datasheet - Page 18

• Manufacturer Part Number: AAT1236
• Manufacturer: Analogic Corporation

20V rated Schottky diodes are recommended for out-
put voltages less than 15V, while 30V rated Schottky
diodes are recommended for output voltages higher
than 15V.
Estimating Schottky Diode Power
Dissipation
The switching period is divided between ON and
OFF time intervals:
During the ON time, the N-channel power MOSFET
is conducting and storing energy in the boost induc-
tor. During the OFF time, the N-channel power
MOSFET is not conducting. Stored energy is trans-
ferred from the input battery and boost inductor to
the output load through the output diode.
Duty cycle is defined as the ON time divided by the
total switching interval:
The maximum duty cycle can be estimated from
the relationship for a continuous mode boost con-
verter. Maximum duty cycle (D
at minimum input voltage (V
18
Manufacturer
Diodes, Inc.
ON Semi
ON Semi
Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Loads
D
MAX
D =
F
1
=
= T
S
= T
T
V
ON
Part Number
B0520WS
MBR130LSFT
MBR0530T
ON
OUT
ON
T
⋅ F
+ T
ON
V
- V
+ T
IN(MIN)
OUT
S
OFF
MAX
IN(MIN)
OFF
(select T
) is the duty cycle
):
J
< 110°C in application circuit).
Current (A)
Rated I
0.50
1.00
0.50
F(AV)
1
High Efficiency White LED Drivers
The average diode current during the OFF time can
be estimated:
The V
the average current during the off time. The aver-
age diode current is equal to the output current:
The average output current multiplied by the for-
ward diode voltage determines the loss of the out-
put diode:
For continuous LED currents, the diode junction
temperature can then be estimated:
External Schottky diode junction temperature
should be below 110ºC, and may vary depending
on application and/or system guidelines. The diode
θ
area on the cathode. However, adding additional
heat-sinking metal around the anode may degrade
EMI performance. The reverse leakage current of
the rectifier must be considered to maintain low
quiescent (input) current and high efficiency under
light load. The rectifier reverse current increases
dramatically at elevated temperatures.
JA
Voltage (V)
can be minimized with additional metal PCB
Rated
F
of the Schottky diode can be estimated from
20
30
30
T
J(DIODE)
for Backlight and Keypad
P
LOSS(DIODE)
I
AVG(OFF)
= T
I
AVG(TOT)
Resistance
(θ θ
AMB
Thermal
JA
= I
= I
=
, °C/W)
+ θ
426
325
206
1 - D
= I
OUT
AVG(TOT)
JA
I
OUT
OUT
· P
· V
MAX
1
LOSS(DIODE)
F
· V
F
1236.2007.01.1.0
SOD-323
SOD-123
SOD-123
Case