MAX16838ATP/V+T Maxim Integrated, MAX16838ATP/V+T Datasheet - Page 13

• Manufacturer Part Number: MAX16838ATP/V+T
• Description: LED Lighting Drivers Integrated 2-Channel High-Brightness LED Drivers with High-Voltage DC-DC Controller
• Manufacturer: Maxim Integrated

Specifications of MAX16838ATP/V+T

• Input Voltage: 4.75 V to 40 V
• Maximum Supply Current: 3.1 mA
• Power Dissipation: 2051 mW

Integrated, 2-Channel, High-Brightness LED Driver
The voltage at each of the current-sink outputs (OUT_)
is the difference between the DC-DC regulator output
voltage (V
string connected to the output (OUT_). The DC-DC con-
verter then adjusts V
the lowest voltage at OUT_ is 1V relative to LEDGND. As
a result, the device minimizes power dissipation in the
current sinks and still maintains LED current regulation.
For efficient adaptive control functionality, use an equal
number of HB LEDs of the same forward voltage rating
in each string.
The MAX16838 includes a fast current-limit comparator
to terminate the on-cycle during an overload or a fault
condition. The current-sense resistor (R
between the source of the internal MOSFET and ground
sets the current limit. The CS input has a 0.3V voltage
trip level (V
R
where I
MOSFET.
The MAX16838 features two undervoltage lockouts:
UVLO
threshold for V
lockout threshold for V
The MAX16838 features a soft-start that activates during
power-up. The soft-start ramps up the output of the con-
verter in 64 steps in a period of 100ms (typ), unless both
strings reach regulation point, in which case the soft-start
would terminate to resume normal operation immediately.
Once the soft-start is over, the internal soft-start circuitry
is disabled and the normal operation begins.
The MAX16838 oscillator frequency is programmable
between 200kHz and 2MHz using one external resis-
tor (R
MOSFET driver output switching frequency is the same
CS
:
RT
IN
Oscillator Frequency/External Synchronization
PEAK
) connected between RT and SGND. The PWM
with High-Voltage Boost and SEPIC Controller
and UVLO
LED
CS
is the peak current that flows through the
) and the total forward voltage of the LED
). Use the following equation to calculate
IN
______________________________________________________________________________________
R
is 4.3V (typ) and the undervoltage
CS
VCC
LED
CC
= (V
. The undervoltage lockout
is 4V (typ).
until the output channel with
CS
)/I
PEAK
Undervoltage Lockout
CS
Current Limit
) connected
Soft-Start
Figure
as the oscillator frequency. The oscillator frequency is
determined using the following formula:
where R
Synchronize the oscillator with an external clock by
AC-coupling the external clock to the R
capacitor used for the AC-coupling should satisfy the
following relation:
where R
The pulse width for the synchronization signal should
satisfy the following relations:
where t
t
is the synchronization pulse voltage level. See Figure 1.
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at DRV. The LDO regulator
output supports up to 30mA current, enough to provide
power to the internal control circuitry and the gate driver.
CLK
V
is the synchronization clock time period, and V
1. Synchronizing External Clock Signal
S
PW
RT
RT
C
is in ω.
is in I.
SYNC
is the synchronization source pulse width,
t
PW
f



SW
0.8
≤
= (7.342X10




−
9.862
t
t
t
R
CLK
t
CLK
PW
PW
T
−
V
V
S
S
0.144 10
t
CLK
<



5V LDO Regulator (DRV)
+
9
0.8
/R
V
S
RT
×
>
)(Hz)
3.4
−
3




( F)
RT
µ
input. The
13
S