SGM3141 Datasheet, PDF (9/14 Pages) SG Micro Corp – Charge Pump LED Driver

SGM3141
APPLICATION INFORMATION
Over-Temperature Protection
When the temperature of SGM3141 rises above 145℃,
the over-temperature protection circuitry turns off the
output switches to prevent damage to the device. If the
temperature drops back down below 130℃, the part
automatically recovers and executes a soft-start cycle.
Over-Voltage Protection
The SGM3141 has over-voltage protection. If the output
voltage rises above the 5.5V threshold, the over-voltage
protection shuts off all of the output switches to prevent
the output voltage from rising further. When the output
decreases below 5.2V, the device resumes normal
operation.
Over-Current Protection
The over-current protection circuitry monitors the
average current out of the VOUT = 47mV (Torch Mode) pin.
If the average output current exceeds approximately 1A,
then the over-current protection circuitry shuts off the
output switches to protect the chip.
Component Selection
The SGM3141 charge pump circuit requires 3 capacitors:
4.7μF input, 1μF output and 1μF flying capacitors are
typically recommended. For the input capacitor, a larger
value of 10μF will help reduce input voltage ripple for
applications sensitive to ripple on the battery voltage. All
the capacitors should be surface mount ceramic for low
lead inductance necessary at the 2.2MHz switching
frequency of the SGM3141 and to obtain low ESR, which
improves bypassing on the input and output and
improves output voltage drive by reducing output
resistance. Ceramic capacitors with X5R or X7R
temperature grade are recommended for most
applications.
The input and output capacitors should be located as
close to the VIN and VOUT pins as possible to obtain
best bypassing, and the returns should be connected
directly to the PGND pin or to the thermal pad ground
located under the SGM3141. The flying capacitor should
be located as close to the C1 and C2 pins as possible.
700mA Buck/Boost
Charge Pump LED Driver
To obtain lower output ripple, the C_OUT value can be
increased from 1μF to 2.2μF or 4.7μF with a
corresponding decrease in output ripple. For output
currents of 500mA to 700mA, the recommended C_F flying
capacitor value of 1μF should be used. Output currents in
Flash of 100mA to 400mA can use a 0.47μF C_F but a
minimum 1μF C_OUT is still needed.
Resistor Selection
The sense resistor R_SENSE is determined by the value
needed in the Torch mode for the desired output current
by the equation:
R_SENSE = V_FB/I_OUT where V_FB = 47mV (Torch Mode)
Once the R_SENSE resistor has been selected for Torch
mode, the V_FB voltage can be selected for Flash mode
using the following equation:
V_FB = I_OUT × R_SENSE (Flash Mode) where I_OUT is for Flash
Mode.
Next, the R_SET resistor can be selected for Flash mode
using the following equation:
R_SET = (1.26V/V_FB) × 10.2kΩ (Flash Mode)
For an example of 190mA Torch mode and 600mA Flash
mode, the values of R_SENSE = 0.25Ω, V_FB = 150mV (Flash
Mode), and R_SET = 86.6kΩ are calculated. The power
obtained in the Flash mode would be:
P_FLASH = V_FB × I_OUT = 150mV × 600mA = 90mW
The typical 0603 surface mount resistor is rated 1/10
Watt continuous power and 1/5 Watt pulsed power, more
than enough for this application. For other applications,
the P_FLASH power can be calculated and resistor size
selected. The R_SENSE resistor is recommended to be size
0603 for most applications.
The range of typical resistor values and sizes are shown
here in Table 1.
SG Micro Corp
9
www.sg-micro.com