MAX77342 Datasheet, PDF (23/50 Pages) Maxim Integrated Products – DC-DC Step-Up Converter

MAX77342
1.6A Adaptive DC-DC Step-Up Converter
with High-Side Flash Driver
Overvoltage Protection
The device includes two overvoltage protection circuits.
The first protection mechanism is part of the adaptive
regulation control, and limits the converter output volt-
age to the OVP_D threshold for a duration of t_{OVP_D}
(1.024ms) before the current regulator and the DC-DC
converter are disabled.
The second protection mechanism is set to trigger on a
higher threshold, but has a much faster reaction time. If
the output voltage rises above the OVP_A threshold, the
converter and current regulators are disabled within a
reduced time delay.
RESET OVP_D
TIMER
DCDC_OUT
NO
≥ OVP_D
YES
START OVP_D
TIMER
NO
DCDC_OUT
≥ OVP_A
YES
NO
DCDC_OUT
≥ OVP_D
YES
YES
OVP_D
TIMER EXPIRED
NO
DCDC_OUT
≥ OVP_A
NO
YES
DISABLE DC-DC AND
CURRENT REGULATOR
Figure 5. Overvoltage State Diagram
Low-Side Current Limit
The device provides a programmable current limit for the
low-side switch. This current limit functions as an input
current limit, and is critical for the application, since this
function determines the maximum current that can be
drawn from the input supply. This low-side current limit
is also important for the choice of inductor, since it deter-
mines the minimum saturation current, to avoid the induc-
tor hitting saturation.
If the input current limit is reached during operation, the
low-side switch terminates the cycle and turns on the
high-side switch. This results in a drop of the output volt-
age. The device operates in continuous input current limit
condition, but due to a drop in output voltage, the current
regulator parameters cannot be guaranteed in this mode
of operation. For a duty cycle lower than the minimum
duty cycle the converter cannot limit the current. This is
due to the fact that the current in the inductor does not
discharge sufficiently during the OFF-time to ensure that
the LX peak current does not hit the peak current limit
within the time for the minimum duty cycle. In application
though, this is only an issue if the flash current is set to
80% min of the peak current limit.
LED Current Regulator
The MAX77342 has three internal high-side current regu-
lators. They are connected to two outputs, FLED and IND.
The FLED output is used for flash, torch, and assist light
mode using the following current regulators.
● Flash mode current regulator
● Assist/torch mode current regulator
The IND output is used for indicator and consists of a
single current regulator that is always powered directly
from IN.
Each of the current settings is flexibly controlled by the
I²C interface.
Indicator Mode
Indicator mode operates separate from the torch, assist,
and flash modes, since it has a dedicated output.
The current regulator for IND is directly powered from the
IN, and always regulates to 2.9V (min) or operates in dropout
for V_IN voltages less than 3.0V (V_{IND_DROPOUT_REG}) when
it is used. This is done to ensure that a minimum 2.9V is
always available for the IND interface.
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