MAX1739EEP+ Maxim Integrated Products, MAX1739EEP+ Datasheet - Page 16

• Manufacturer Part Number: MAX1739EEP+
• Description: Display Drivers Wide Brightness Rang e CCFL Backlight Con
• Manufacturer: Maxim Integrated Products

Specifications of MAX1739EEP+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Wide Brightness Range
CCFL Backlight Controllers
Figure 6. DPWM Synchronization
optimized using R14 and R15 as shown in Figure 7.
The resistor-divider can be used to force commutation
as close to the zero-crossing point as possible.
The MAX1739/MAX1839 include power-on reset (POR)
and undervoltage lockout (UVLO) features. The POR
resets all internal registers, such as DAC output, fault
conditions, and all SMBus registers. POR occurs when
VL is below 1.5V. The SMBus input logic thresholds are
designed to meet electrical characteristic limits for VL
as low as 3.5V, but the interface will continue to func-
tion down to the POR threshold.
The UVLO threshold occurs when VL is below 4.2V
(typ) and disables the buck-switch driver.
When the MAX1739/MAX1839 are placed in shutdown,
all IC functions are turned off except the 5V linear regu-
lator that powers all internal registers and the SMBus
interface (MAX1739). The SMBus interface is accessi-
ble in shutdown. In shutdown, the linear regulator out-
put voltage drops to about 4.5V and the supply current
is 6µA (typ), which is the required power to maintain all
internal register states. While in shutdown, lamp-out
detection and buck-switch short-circuit detection latch-
es are reset. The device can be placed into shutdown
by either writing to the MODE register (MAX1739
SMBus mode only) or with SH/SUS.
For safety, during a lamp-out condition, the MAX1739/
MAX1839 limit the maximum average primary-side
transformer voltage (see Sense Resistors) and shut
down the lamp after 2s.
16
SYNCHRONIZATION
______________________________________________________________________________________
SIGNAL
DPWM
SMBus
ADC-
ADC+
500pF
Low-Power Shutdown
10k
Lamp-Out Detection
POR and UVLO
VL
REF
MODE
GND
MAX1739
MAX1839
The lamp-out detection circuitry monitors V
shuts down the lamp if V
(typ) within 2 seconds. This circuitry ignores most puls-
es under 200ns. However, in some cases, a small
capacitor is needed at CSAV to prevent noise from trip-
ping the circuitry. This is especially true in noisy envi-
ronments and in designs with marginal layout.
Ideally, the voltage at CSAV is a half-wave rectified sine
wave. In this case, the CSAV lamp-out threshold is as
follows:
where I
the maximum lamp current (see Sense Resistors). Note:
The formulas assume a worst-case CSAV lamp-out
threshold of 100mV and a maximum CSAV average
voltage of 200mV.
Use MINDAC or limit the brightness code to prevent
setting the lamp current below the CSAV lamp-out
threshold.
STATUS1 bit sets when the lamp-out detection circuit
shuts down the device.
When the buck switch (N1) fails short, there is no volt-
age limiting on the transformer and the input forces
excessive voltage on the transformer secondary. This
Figure 7. Adjusting the ZVC Detection
MAX1739
MAX1839
MIN
SYNC
CTFB
GND
REF
LX
Buck-Switch Short Fault Detection
is the CSAV lamp out threshold, and I
I
MIN
L1
= I
R14
R15
CSAV
MAX
does not exceed 75mV
/ 6
R4
R5
and Protection
T1
CSAV
MAX
and
is