CAT4238_16 Datasheet, PDF (3/12 Pages) ON Semiconductor – High Efficiency 10 LED Boost Converter

CAT4238
Table 3. DC ELECTRICAL CHARACTERISTICS
(V_IN = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified))
Symbol
Parameter
Test Conditions
Min
Typ
Max Units
I_Q
Operating Current
I_SD
Shutdown Current
V_FB
FB Pin Voltage
I_FB
FB pin input leakage
I_LED
Programmed LED Current
V_FB = 0.2 V
V_FB = 0.4 V (not switching)
V_SHDN = 0 V
10 LEDs with I_LED = 20 mA
R1 = 10 W
R1 = 15 W
R1 = 20 W
0.6
1.5
mA
0.1
0.6
0.1
1
mA
285
300
315
mV
1
mA
28.5
30
31.5
mA
19
20
21
14.25
15
15.75
V_IH
SHDN Logic High
V_IL
SHDN Logic Low
Enable Threshold Level
Shutdown Threshold Level
0.8
1.5
V
0.4
0.7
F_SW
Switching Frequency
DC
Maximum Duty Cycle
VIN = 3 V
0.8
1.0
1.3
MHz
92
%
I_LIM
R_SW
I_LEAK
Switch Current Limit
Switch “On” Resistance
Switch Leakage Current
Thermal Shutdown
I_SW = 100 mA
Switch Off, V_SW = 5 V
350
450
600
mA
1.0
2.0
W
1
5
mA
150
°C
Thermal Hysteresis
20
°C
V_UVLO
Undervoltage Lockout (UVLO) Threshold
1.9
V
V_OV-SW
Overvoltage Detection Threshold
40
V
V_OCL
Output Voltage Clamp
“Open LED” with VIN = 5 V
43
45
48
V
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
Pin Description
VIN is the supply input for the internal logic. The device is
compatible with supply voltages down to 2.8 V and up to
5.5 V. It is recommended that a small bypass ceramic
capacitor (4.7 mF) be placed between the VIN and GND pins
near the device. If the supply voltage drops below 1.9 V, the
device stops switching.
SHDN is the shutdown logic input. When the pin is tied to
a voltage lower than 0.4 V, the device is in shutdown mode,
drawing nearly zero current. When the pin is connected to a
voltage higher than 1.5 V, the device is enabled.
GND is the ground reference pin. This pin should be
connected directly to the ground place on the PCB.
SW pin is connected to the drain of the internal CMOS
power switch of the boost converter. The inductor and the
Schottky diode anode should be connected to the SW pin.
Traces going to the SW pin should be as short as possible
with minimum loop area. An over-voltage detection circuit
is connected to the SW pin. When the voltage reaches 40 V,
the device enters a low power operating mode preventing the
SW voltage from exceeding the maximum rating.
FB feedback pin is regulated at 0.3 V. A resistor connected
between the FB pin and ground sets the LED current
according to the formula:
0.3 V
I_LED + _R1
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin #
Name
Function
1
SW
Switch pin. This is the drain of the internal power switch.
2
GND
Ground pin. Connect the pin to the ground plane.
3
FB
Feedback pin. Connect to the last LED cathode.
4
SHDN
Shutdown pin (Logic Low). Set high to enable the driver.
5
VIN
Power Supply input.
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