|
Basic Information
Question 1
In the HT77 PFM Step-up DC/DC converter, can you explain the meaning of PFM?
Answer
PFM is short for Pulse Frequency Modulation. In this type of waveform the repetition rate of the pulse waveform is modulated.
Question 2
Does the HT77XX series of devices have a chip enable pin? Answer
Only the SOT25 packages in the HT77XX series have a chip enable pin. The SOT25 package types have 5 pins, CE, NC, GND, LX and VOUT. The CE pin is the chip enable pin. The other package types, TO92 and SOT89, have only 3 pins, GND, LX and VOUT, but no CE pin.
The CE chip enable pin, controls whether the HT77XX enters its normal operating mode or whether it enters the shutdown mode. In the shutdown mode the HT77XX’s internal functions, such as reference block, gain block and feedback control block are all switched off, which reduces the device’s current consumption to very low levels, around 0.5uA.When the device is shutdown, the HT77XX output voltage will be equal to the input voltage minus the Schottky diode voltage. This output voltage will slowly fall according to the values of the output capacitor and load. Because this output voltage cannot fall to zero quickly, it is necessary to use the external circuitry to do so, such as that which is shown in the diagram where an external PMOS FET is used to reduce the output voltage to zero. When the external control line is high, the device is enable and the power is on, when the line is low, the device is disabled and the power is off.
Question 3
What is the output voltage tolerance on the HT77XX PFM Step-up DC/DC converters?
Answer
The HT77XX series PFM step-up DC/DC converter output voltage tolerance is
+/-2.5%.
Question 4
What package types are available for the HT77XX DC/DC converter devices?
Answer
The HT77XX devices are supplied in TO92, SOT89 and SOT25 package types.
Question 5
What output voltage ranges are supplied for the HT77XX series DC/DC Converters?
Answer
The series is supplied in fixed voltage types of 2.7V, 3.0V, 3.3V, 3.7V and 5.0V.
Question 6
What is the input voltage range for the HT77XX series DC/DC Converters?
Answer
The HT7727, HT7730, HT7733 and HT7737devices have an input voltage range of 0.6~6.0V while the HT7750 has an input voltage range of 0.7V~6.0V.
Question 7
What is the conversion efficiency of the HT77XX series DC/DC Converters?
Answer
The HT77XX series DC/DC Converters can reach an efficiency of 85%.
Question 8
On devices marked with a "HT77XX#" and "77XX#", can you explain what the "#" within the mark means?
Answer
The "#" mark is to indicate a lead-free product. According to the different package types, the HT77XX series of lead free devices, has three types of mark: HT77XX# for SOT-89 packages, 77XX# for SOT-25 packages, for the TO-92 packages, the "#" lead free indicator is placed behind the product date code.
Question 9
What is the operating temperature range for the HT77XX device range?
Answer
The operating temperature range for the HT77XX device range is from 0℃ to 70℃.
Application Description
Question 1
What points should be noted when using the HT77XX series DC/DC Converters in a practical circuit?
Answer
Because the HT77XX series devices use PFM (Pulse Frequency Modulation) to implement their DC to DC conversion, to reduce ripple and provide a stable output voltage, an inductor of value around 100uH should be connected to the voltage input.
|
