BOOST Converter Analog/Digital Adjusted Output Voltage TPS61045 MAX1932

DIGITALLY ADJUSTABLE BOOST CONVERTER

The TPS61045 is a high frequency boost converter with digitally programmable output voltage and true shutdown. During shutdown, the output is disconnected from the input by opening the internal input switch. This allows a controlled power up/down sequencing of the display. The output voltage can be increased or decreased in digital steps by applying a logic signal to the CTRL pin. The output voltage range, as well as the output voltage step size, can be programmed with the feedback divider network. With a high switching frequency of up to 1 MHz, the TPS61045 allows the use of small external components and together, with the small 8-pin QFN package, a minimum system solution size is achieved.

• Input Voltage Range . . .1.8 V to 6 V
• Output voltage of up to 28V possible
• Up to 85% Efficiency
• Digitally Adjustable Output Voltage Control
• Disconnects Output From Input During Shutdown
• Switching Frequency . . . Up to 1 MHz
• No Load Quiescent Current . . . 40 µA Typ
• Thermal Shutdown Mode
• Shutdown Current . . . 0.1 µA Typ
• Available in Small 3mm × 3mm QFN package
• APPLICATIONS
  • LCD Bias Supply For Small to Medium LCD Displays
  • OLED Display Power Supply
    • PDA, Pocket PC, Smart Phones
    • Handheld Devices
    • Cellular Phones

DAC = 0V : Vo = 1.233 * ( 2200 / 390 ) + 1.233 * ( 1 + 2200/180 ) = 6.95V + 16.303V = 23.253V

DAC = 1.233V : V0 = 1.233 * ( 1 + 2200/180 ) = 16.303V

SETTING THE OUTPUT VOLTAGE (see Figure 1)

When the converter is programmed to the minimum output voltage,
the DAC output (DO) equals the reference voltage of 1.233 V (typ).

Therefore, only the feedback resistor network (R1) and (R2) determines the output voltage under these conditions.
This gives the minimum output voltage possible and can be calculated as:

The maximum output voltage is determined as the DAC output (DO) is set to 0 V:

the DAC output DO (pin 3) one-step where one step is typically 19.6 mV. ( 0..63 : 6 Bit DAC )

The DAC output pin (DO) drives an external resistor (R3) connected to the external feedback
divider. The DO output has a typical output voltage range from 0 V to Vref (1.233V). If the DO output voltage is
set to 0 V, the external resistor (R3) is more or less in parallel to the lower feedback resistor (R2) giving the
highest output voltage. Programming the DO output to Vref gives the lowest output voltage. Internally, a 6-bit DAC
is used with 64-steps and 0 as the first step. This gives a typical voltage step of 19.6 mV which is calculated as:

A voltage step on DO of 19.6mV (typ) changes the output voltage by one step and is calculated as:

The possible output voltage range is determined by selecting R1, R2 and R3.

A possible larger output voltage range gives a larger output voltage step size.

The smaller the possible output voltage range, the smaller the output voltage step size.

DIGITAL INTERFACE (CTRL)

When the CTRL pin is pulled high the device starts up with softstart
and the DAC output voltage (DO) sets to its center voltage with a typical output voltage of 607 mV.

The output voltage can be programmed by pulling the CTRL pin low for a certain period of time.

Depending on this time period the internal DAC voltage increases or decreases one digital step,
as outlined in Table 2 and Figure 16.

Programming the DAC output V(DO) to 0 V places R3 in parallel to R2, which gives the maximum output voltage.

If the DAC is programmed to its maximum output voltage equal to the internal reference voltage, typically V(DO) = 1.233 V,

then the output has its minimum output voltage.

数控、0.5%精度、更安全的APD偏置电源

MAX1932为光学接受器中的雪崩光电二极管(APD)产生一个低噪声、高电压输出。通过一个恒定频率的、脉宽调制(PWM) boost拓扑及一个独特的结构――该结构在反馈回路中加入可选择的RC或者LC后滤波器仍可保持稳定调压，得以达到非常低的输出纹波和噪声。一个精确的参考和误差放大器可以保持0.5%输出电压准确度。

MAX1932可以保护贵重的APD，抵制不利的工作条件，同时提供最优的偏压。传统的boost转换器通过测量开关电流来进行保护，而MAX1932集成了精确的高端限流特性来保护雪崩条件下的APD。一个限流标志位指示精确的雪崩击穿点以方便APD工作点的校准。MAX1932控制方式防止输出过冲和欠冲，可使APD安全工作而不发生数据丢失。

输出电压可以通过外部电阻器、内部8位DAC、外部DAC或者其他电压源来进行精确的调节。

输出范围和偏移都是可通过外部电阻器独立调节的。这可在要求一个受限制电压范围的应用中充分利用DAC的分辨率，

如输出4.5V至15V、4.5V至45V、20V至60V或40V至90V。

• 电路板面积小
• 电路高度<2mm
• 2.7V至5.5V输入电压
• 4.5V至90V输出电压范围
• 无过冲
• 精确的高端限流
• 雪崩指示标记
• 8位SPI兼容DAC
• 和外部DAC兼容
• 0.5%输出电压精度
• 低输出电压纹波(< 1mV)
• 小尺寸的12引脚，4mm x 4mm微型QFN封装

Output Control DAC

DACOUT = DAC code x (1.25V/256) + 1.25V/256.

An internal digital-to-analog converter can be used to control the output voltage of the DC-DC converter (Figure 2).

The DAC output is changed through an SPI™ serial interface using an 8-bit control byte.

On power-up, the DAC defaults to FF hex (1.25V), which corresponds to a minimum boost converter output voltage.
DAC Code = 0xFF : 0xFF * 1.25 / 256 + 1.25 / 256 = 1.25V

Alternately, the output voltage can be set with external resistors, an external DAC, or a voltage source.

Output span and offset are independently settable with externnal resistors.

See the Applications Information section for output control equations.

Output and DAC Adjustments Range

Many biasing applications require an adjustable output voltage,
which is easily obtained using the MAX1932’s DAC output (Figure 2).

The DAC output voltage is given by the following equation:

On power-up, DACOUT defaults to FF hex or 1.25V,
which corresponds to the minimum VOUT output voltage.

The voltage generated at DACOUT is coupled to FB through R6.
DACOUT can sink only 50µA so:

R6 >= 1.25V / 50uA = 25K

Select the minimum output voltage (VOUTFF),
and the maximum output voltage (VOUT01)
for the desired adjustment range.

R5 sets the adjustment span using the following equation:

R5 = (VOUTFF - VOUT01) * (R6/1.25V)

R8 sets the minimum output of the adjustment range with the following equation:

R8 = (1.25V ✕ R5)/(VOUTFF)

Setting the Output Voltage without  the DAC

Adjust the output voltage by connecting a voltagedivider from the output (VOUT) to FB
(Figure 2 with R6 omitted).

Select R8 between 10kΩ to 50kΩ. Calculate R5 with the following equation:

R5 = R8 * ( VOUT / 1.25V - 1 ) ::: VOUT = 1.25V * ( 1 + R5/R8 )