MAX16929BGUI datasheet(18/25 Pages) MAXIM

18 / 25 page

�� Maxim Integrated Products 18

MAX16929

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

Table 3. Compensation Component Values

To further optimize transient response, vary RCOMPV

in 20% steps and CCOMPV in 50% steps while observ-

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 CCOMPI:

CCOMPI ≤ 550 × 10-6 × L/fSW × (VSH + VSCHOTTKY - VINA)

where fSW = 2.2MHz.

p-Channel FET Selection

The p-channel FET used to gate the boost converter’s

input should have low on-resistance. Connect a resistor

(RSG) between the source and gate of the FET. Under

normal operation, RSG carries a gate drive current of

55FA and the resulting gate source voltage (VGS) turns

on the FET. When the gate drive is removed under a fault

condition or in shutdown, RSG bleeds off charge to turn

off the FET. Size RSG to produce the VGS needed to turn

on the FET.

1.8V/3.3V Regulator Controller

npn Bipolar Transistor Selection

There are two important considerations in selecting the

pass npn bipolar transistor: current gain (hFE) and power

dissipation. Select a transistor with an hFE high enough to

ensure adequate drive capability. This condition is satis-

fied when IDR x (hFE + 1) is greater than the maximum

load current. The regulator can source IDR = 4.5mA (min).

The transistor should be capable of dissipating:

PNPN_REG = (VINA - VREG_OUT) × ILOAD(MAX)

where VREG_OUT = 1.8V or 3.3V. Bypass DR to ground

with a 0.1FF ceramic capacitor. For applications in which

the boost output current exceeds 300mA, connect a

30kI resistor from DR to ground.

Supply Considerations

INA needs to be at least 4.5V for the 3.3V regulator to

operate properly.

Charge Pumps

Selecting the Number of Charge-Pump Stages

For most applications, a single charge-pump stage is

sufficient, as shown in the Typical Application Circuit.

Connect the flying capacitors to LXP. The output voltages

generated on the storage capacitors are given by:

VCP = 2 x VSH + VSCHOTTKY - 2 x VD

VCN = -(VSH + VSCHOTTKY - 2 x VD)

where VCP is the positive supply for the positive-gate volt-

age regulator, and VCN is the negative supply for the neg-

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). Figure 2 and Figure 3

show the configuration of a multistage charge pump for

both positive and negative output voltages.

For mutistage charge pumps the output voltages are:

VCP = VSH + n × (VSH + VSCHOTTKY - 2 x VD)

VCN = -n × (VSH + VSCHOTTKY - 2 x VD)

Figure 2. Multistage Charge Pump for Positive Output Voltage

Figure 3. Multistage Charge Pump for Negative Output Voltage

VSH (V)

ISH (mA)

200

VINA (V)

3.3

PIN (W)

1.75

3.75

L (µH)

RCOMPV (kI)

CCOMPV (pF)

220

180

CCOMPI (pF)

820

330

VSH

VCP

LXP

VCN

LXP

MAX16929BGUI датащи(PDF) 18 Page - Maxim Integrated Products

MAX16929BGUI датащи(HTML) 18 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

датащи скачать

ссылки URL