MC34845BEPR2 Freescale Semiconductor, MC34845BEPR2 Datasheet - Page 10

• Manufacturer Part Number: MC34845BEPR2
• Description: IC LED DVR BACKLIGHT 6CH 24QFN
• Manufacturer: Freescale Semiconductor
• Type: Backlight, White LED, Color LEDr

Specifications of MC34845BEPR2

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Backlight
• Frequency: 270kHz ~ 330kHz
• Voltage - Supply: 5 V ~ 21 V
• Voltage - Output: 8 V ~ 60 V
• Mounting Type: Surface Mount
• Package / Case: 24-QFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Efficiency: 90%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

BOOST CONVERTER
(DHC) loop to automatically set the output voltage needed to
drive the LED strings. The DHC is designed to operate under
specific pulse width conditions in the LED drivers. It operates
for pulse widths higher than 400 ns. If the pulse widths are
shorter than specified, the DHC circuit will not operate and
the voltage across the LED drivers will increase to a value
given by the OVP, minus the total LED voltage in the LED
string. It is therefore imperative to select the proper OVP level
to avoid exceeding the max off state voltage of the LED
drivers (45V).
externally through a type 2 network on the COMP pin. A
modification of the compensation network is suggested to
minimize the amplitude of the ripple at V
the suggested compensation network are shown in
10
output current. An Over-current Protection circuit limits the
output current cycle-by-cycle to I
longer than 10 ms, then the device will shut down. The
frequency of the boost converter is internally set to 300 kHz,
600 kHz or 1.2 MHz, depending on the device’s version.
IC comes out of shutdown mode, the soft start period lasts for
t
an internally fixed OVP value of 60V (typical) which serves as
a secondary fault protection mechanism, in the event the
externally programmed OVP fails (i.e. resistor divider opens
up). While the internal 60V OVP detector can be used
exclusively without the external OVP network, this is only
recommended for applications where the LED string voltage
approaches 55 V or more. The OVP level can be set by using
an external resistor divider connected between the output
SS
Figure 5. Power up sequence case 2, VIN applied after
The boost converter uses a Dynamic Headroom Control
The boost operates in current mode and is compensated
An integrated 2.0A minimum FET supplies the required
The boost also includes a soft start circuit. Each time the
Over-voltage Protection is also included. The device has
VOUT
.
PWM
between 0V and 5V should be not higher than 2ms
and 11.
FUNCTIONAL DEVICE OPERATION
INTRODUCTION
10
34845
the ENABLE and PWM signals. VIN ramp up time
VIN
EN
5V
2 ms
VIN ramp
OCP
UVLO Rising
. If the condition exists
Boost
Soft Start
OUT
. The details of
Figures
voltage and ground with its output connected to the OVP pin.
The OVP can be set up to 60V by varying the resistor divider
to match the OVP internal reference of 6.9V (typical).
LED DRIVER
LED strings to within ±2% maximum. The current in the
strings is set using a resistor tied to GND from the ISET pin.
The LED current level is given by the equation: RSET = 153/
ILED. The accuracy of the RSET resistor should be 0.1% for
best performance.
LED ERROR DETECT
level. If there is still no current in the LED string, the LED
channel is turned off and the output voltage ramps back down
to normal operating level.
is greater than the SFDV threshold (7.0 V typical), then the
device will turn off that channel. However if the on-time of the
channels is less than 10 μs, the SFDV circuit will not disable
any of the channels, regardless of the voltage across them.
or applying a complete power-on-reset (POR).
WAKE OPERATION
low power consumption (shutdown mode) without the need of
an extra logic signal for enable. This is achieved by
connecting the WAKE and PWM pins together, and tying the
EN pin to ground. In this configuration, the PWM signal is
used to control the LED channels, while allowing low power
consumption by setting the device into its shutdown mode
every time the PWM signal is kept low for longer time than the
WAKE time out of 27 ms.
OVER-TEMPERATURE SHUTDOWN AND
TEMPERATURE CONTROL CIRCUITS
internal temperature exceeds the over-temp threshold
OTT
Once the temperature falls below the low level threshold, the
device is re-enabled.
FAIL PIN
is detected. However, if an error such as an LED channel
open or boost over-current is detected, the FAIL pin goes into
high-impedance. Once a failure is detected, the FAIL pin can
be cleared by recycling the EN pin or applying a complete
power-on-reset (POR). If the detected failure is an Over-
current time-out, the EN pin or a POR must be cycled/
executed to restart the part.
The 6 channel LED driver provides current matching for 6
If an LED is open, the output voltage ramps to the OVP
If LEDs are shorted and the voltage in any of the channels
All the LED errors can be cleared by recycling the EN pin
The WAKE pin provides the means to set the device for
The 34845 includes over-temperature protection. If the
The FAIL pin is at its low-impedance state when no error
SHUTDOWN
, then the device shuts down all functions.
Analog Integrated Circuit Device Data
Freescale Semiconductor