MAX16928EVKIT# Maxim Integrated, MAX16928EVKIT# Datasheet - Page 13

• Manufacturer Part Number: MAX16928EVKIT#
• Description: Power Management IC Development Tools Eval Kit MAX16928 (Complete Automotive TFT-LCD Display Power Supply)
• Manufacturer: Maxim Integrated
• Series: MAX16928r

To further optimize transient response, vary R
in 20% steps and C
ing transient-response waveforms. The ideal transient
response is achieved when the output settles quickly with
little or no overshoot. Connect the compensation network
to the analog ground plane.
Use the following formula to calculate the value for C
The p-channel FET used to gate the boost converter’s
input should have low on-resistance. Connect a resistor
(R
normal operation, R
55FA and the resulting gate source voltage (V
on the FET. When the gate drive is removed under a fault
condition or in shutdown, R
off the FET. Size R
on the FET.
There are two important considerations in selecting the
pass npn bipolar transistor: current gain (h
dissipation. Select a transistor with an h
to ensure adequate drive capability. This condition is
satisfied when I
mum load current. The regulator can source I
(min). The transistor should be capable of dissipating:
where V
with a 0.1FF ceramic capacitor. For applications in which
the boost output current exceeds 300mA, connect a
30kI resistor from DR to ground.
INA needs to be at least 4.5V for the 3.3V regulator to
operate properly.
Figure 2. Multistage Charge Pump for Positive Output Voltage
Maxim Integrated
LXP
V
SG
SH
C
COMPI
P
) between the source and gate of the FET. Under
NPN_REG
REG_OUT
Automotive TFT-LCD Power Supply with Boost
≤ 950 × 10
DR
= (V
1.8V/3.3V Regulator Controller
= 1.8V or 3.3V. Bypass DR to ground
SG
x (h
INA
COMPV
SG
-6
to produce the V
npn Bipolar Transistor Selection
FE
× L/(V
carries a gate drive current of
– V
+ 1) is greater than the maxi-
Converter and Gate Voltage Regulators
REG_OUT
SG
in 50% steps while observ-
SH
p-Channel FET Selection
bleeds off charge to turn
Supply Considerations
+ V
SCHOTTKY
) × I
GS
FE
LOAD(MAX)
needed to turn
FE
high enough
) and power
DR
- V
GS
= 4.5mA
COMPV
INA
COMPI
) turns
)
V
CP
:
For most applications, a single charge-pump stage is
sufficient, as shown in the
Connect the flying capacitors to LXP. The output voltages
generated on the storage capacitors are given by:
where V
age regulator, and V
ative-gate voltage regulator. Where larger output voltages
are needed, use multistage charge pumps (however, the
maximum charge-pump voltage is limited by the absolute
maximum ratings of CP and DRVN).
show the configuration of a multistage charge pump for
both positive and negative output voltages.
For mutistage charge pumps the output voltages are:
For highest efficiency, choose the lowest number of
charge-pump stages that meets the output requirement.
The number of positive charge-pump stages needed is
given by:
and the number of negative charge-pump stages is
given by:
where n
es, n
V
age, V
voltage, V
Figure 3. Multistage Charge Pump for Negative Output Voltage
GH
V
LXP
CN
CN
V
is the positive-gate voltage regulator output volt-
CP
GL
Selecting the Number of Charge-Pump Stages
CP
CP
V
is the number of negative charge-pump stages,
V
CN
= V
V
SH
is the negative-gate voltage regulator output
CP
is the positive supply for the positive-gate volt-
n
CN
is the number of positive charge-pump stag-
n
CN
= -n × (V
CP
SH
is the boost converter’s output voltage, V
= 2 x V
= -(V
=
=
+ n × (V
V
V
SH
V
SH
CN
SH
GH
SH
SH
+V
|V
+
+ V
is the negative supply for the neg-
+V
GL
+ V
V
SH
+ V
SCHOTTKY
SCHOTTKY
SCHOTTKY
DROPOUT
|+V
SCHOTTKY
+ V
SCHOTTKY
Typical Operating
DROPOUT
SCHOTTKY
MAX16928
Figure 2
− ×
− ×
−
- 2 x V
Charge Pumps
2 V
2 V
V
- 2 x V
- 2 x V
SH
- 2 x V
D
D
and
D
D
)
D
)
Figure 3
D
Circuit.
)
13
D