MAX16928CGUP/V+T Maxim Integrated, MAX16928CGUP/V+T Datasheet - Page 10

• Manufacturer Part Number: MAX16928CGUP/V+T
• Description: LCD Drivers Automotive TFT Power Supply
• Manufacturer: Maxim Integrated

Specifications of MAX16928CGUP/V+T

• Rohs: yes

The high-frequency 2.2MHz operation of the boost con-
verter moves switching noise outside of the AM band.
The device achieves enhanced EMI performance by
modulating the switching frequency by Q4%. The modu-
lating signal is pseudorandom and changes each switch-
ing period (i.e., f
Immediately after power-up, coming out of shutdown,
or going into autoretry, the boost converter performs a
short-circuit detection test on the output by connecting
the input (INA) to the switching node (LXP) through an
internal 50I resistor.
If the resulting voltage on LXP exceeds 1.2V, the device
turns on the external pMOS switch by pulling GATE low.
The boost output ramps to its final value in 15ms.
An overloaded or shorted output is detected if the result-
ing voltage on LXP is below 1.2V. The external pMOS
switch remains off and the converter does not switch.
After the fault blanking period of 238ms, the device pulls
PGOOD low and starts the autoretry timer.
The short-circuit detection feature places a lower limit
on the output load of approximately 46I when the input
voltage is 3V.
PGOOD signals whether all the regulators and the boost
converter are operating normally. PGOOD is an open-
drain output that pulls low if any of the following faults
occur:
1) The boost output voltage falls below 85% of its set
2) The positive-gate voltage regulator output (V
3) The negative-gate voltage regulator output (V
4) The LXP voltage is greater than 21V (typ).
5) The positive charge-pump voltage (V
6) The 1.8V/3.3V regulator output voltage falls below
If any of the first three fault conditions persists for longer
than the 238ms fault blanking period, the device pulls
PGOOD low, turns off all outputs, and starts the autoretry
timer.
Maxim Integrated
value.
below 85% of its set value.
below 85% of its set value.
than 30.5V (typ).
85% of its nominal value.
Automotive TFT-LCD Power Supply with Boost
SS
= 2.2MHz).
Spread-Spectrum Modulation
Fault Conditions and PGOOD
Converter and Gate Voltage Regulators
CP
) is greater
GH
GL
Startup
) falls
) falls
If either condition 4 or 5 occurs, the device pulls PGOOD
low and turns off all outputs immediately. The device initi-
ates startup only after the fault has cleared.
If the last condition occurs, the device pulls PGOOD low,
but does not turn off any of the outputs.
During startup, PGOOD is masked and goes high as
soon as the 1.8V/3.3V regulator controller turns on. This
regulator turns on as soon as V
undervoltage lockout threshold.
When the autoretry counter finishes incrementing after
1.9s, the device attempts to turn on the boost con-
verter and gate voltage regulators in the order shown
in
the fault condition persists. A fault on the 1.8V/3.3V regu-
lator output causes PGOOD to go low, but does not result
in the device shutting down and going into autoretry.
The effective current limit of the boost converter is
reduced by the internally injected slope compensation by
an amount dependent on the duty cycle of the converter.
The effective current limit is given by:
where I
1.1A or 2.2A, depending on the boost converter current-
limit option, D is the duty cycle of the boost converter,
and C
input. Estimate the duty cycle of the converter using the
formulas shown in the
The 1.8V/3.3V regulator controller delivers 4.5mA (min)
to an external load. Connect FB to DR for a regulated
1.8V/3.3V output.
For higher output capability, use an external npn transis-
tor as shown in the
capability of the regulator is then increased by the cur-
rent gain of the transistor (h
transistor, use DR as the base drive and connect FB to
the transistor’s emitter. Bypass the base to ground with a
0.1FF ceramic capacitor.
If the boost output current is greater than 300mA, con-
nect a 30kI resistor between DR and GND.
Table
I
COMPI
LIM(EFF)
LIM(EFF)
1. The device continues to autoretry as long as
is the value of the capacitor at the COMPI
=192 10
is the effective current limit, I
1.8V/3.3V Regulator Controller
Typical Operating
×
Design Procedure
-12
×
FE
I
LIM_DC_0
). When using an external
MAX16928
INA
exceeds the INA
Circuit. The drive
Current Limit
×
section.
C
COMPI
D
LIM_DC_0
Autoretry
10
=