SC5010H View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC5010H
Semtech Corporation
'SC5010H' PDF : 36 Pages View PDF
SC5010H
Applications Information (continued)
Boost Converter Operation
The SC5010H includes a boost controller with program-
mable switching frequency. It applies current-mode
control method with integrated compensation loop. The
clock (see block diagram) from the oscillator sets the latch
and turns on the external power MOSFET, which serves as
the main power switch. The current flowing through this
switch is sensed by the current sense resistor in series
with the switch. The sensed switch current is summed
with the slope-compensated ramp and fed into the mod-
ulating input of the PWM comparator. When the modulat-
ing ramp intersects the error amplifier output (COMP),
the latch is reset and the power MOSFET is turned off. The
sense resistor also sets the peak current limit of the power
MOSFET, IOCP using the following equation:
IOCP[A] = 0.4 / RCS [Ω]
The current-mode control system contains two loops. For
the inner current loop, the Error Amplifier (EA) output
(COMP) controls the peak inductor current. In the outer
loop, the EA regulates the output voltage for driving the
LED strings.
Boost Converter Switching Frequency Selection
The resistor between FSET and GND sets the boost con-
verter switching frequency (200kHz to 2.2MHz) using the
following equation:
fSW [kHz] = 105/ RFSET [kΩ]
Higher switching frequency allows the use of low profile
height inductor for space-constrained and cost-sensitive
applications.
Over-Voltage Protection (OVP)
SC5010H features programmable output over-voltage pro-
tection preventing damage to the IC and output capacitor
in the event of LED string open-circuit. The boost converter
output voltage is sensed at the OVP pin through resistor
voltage divider. The OVP trip threshold (refer to detailed
application circuit on page 21) can be calculated using the
following equation.
Output OVP Trip Voltage [V] = 1.2 X (R11 + R10) / R10
When the OVP pin voltage exceeds 1.23V, the boost con-
verter turns off and the FLT pin is pulled low. When the
OVP pin voltage falls below the OVP threshold (falling),
the boost converter restarts and the FLT pin is released.
There is 10mV hysteresis between OVP pin threshold
(falling) and OVP pin threshold (rising). This results in an
output voltage hysteresis given by:
Output OVP Hysteresis[mV] = 10 X (R11 + R10) / R10
LED Current Sink
The SC5010H provides 8 current sinks and each can sink
up to 50mA current. It incorporates LED string short-
circuit protection (trip level programmable and can be
disabled as well), LED string open-circuit protection.
LED String Peak Current Programming
LED string peak current (at 100% dimming) can be set by
selecting resistor RISET, connected between ISET and GND.
The relationship between RISET resistance and single LED
string peak current is calculated using the following
equation:
ILED [mA] = (1055 X 1.23) / RISET [kΩ]
The LED string current can be programmed up to 50mA.
Unused Strings
The SC5010H may be operated with less than 8 strings. In
this mode of operation, all unused IO pins should be con-
nected to ground. During startup, these unused strings are
detected and disabled while other active strings work
normally.
LED Short-Circuit Protection (SCP)
SC5010H features a programmable LED short protection.
This allows the part to be customized based on the LED VF
mismatches between the LED strings. If one or more LEDs
are detected as short-circuited, the corresponding string
will be latched off. The voltages on all IO pins are monitored
to check if any IO pin exceeds the SCP trip point (The IO
voltage for LED string with faulty short-circuit LED(s) will be
higher than other normal IO pin voltages). This LED Short-
Circuit Protection (SCP) trip level (see detailed application
circuit on page 21) is given by the following equation.
VSCP_Trip [V] = 20 X (1.23 X R4) / (R4 + R5)
16
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