Datasheet PAM8907 (Diodes) - 6

PAM8907 Application Information
(continued)
Boost Regulator
The PAM8907 boost regulator is a conventional current-mode controller with the following enhanced features:
Under Voltage Lock Out (ULVO)
: When the input supply (VIN) drops below the UVLO value, the Boost regulator will switch off. Typical UVLO value is 1.6V
Over Temperature Protection (OTP)
: When PAM8907 die temperature is higher than OTP threshold, the Boost regulator will switch off, and

restart after OTP condition is removed. Typical OTP value is set at +160°C.
N VOUT Under Voltage (UV) Protection:
When the Boost regulator output voltage is lower than the pre-set threshold, it will trigger VOUT UV
IO
protection, and the device will go to hiccup mode in order to reduce power supply current.
T VOUT Over-Voltage (OV) Protection:
When the Boost regulator output voltage is higher than the pre-set threshold, it will trigger VOUT OV
A
protection, and the device will switch off until VOUT OV condition is removed.
M R Soft-Start:
The Boost regulator voltage setting is designed to always operate under soft-start operation, which can reduce in-rush current.
O
Typical soft start time is set around 1.1ms.
F Over Current Protection (OCP)
: The Boost regulator has a built-in cycle-by-cycle over current protection.
IN SLEEP:
The Boost regulator will go to sleep mode under light-load condition.
D E C
The PAM8907 has designed the boost regulator as current-mode controller with two control loops, which work together in maintaining a constant
N
output voltage and supply the required load current. The inner current control loop provides cycle-by-cycle current limiting, while the output control
A
loop provides output voltage control. When the boost converter is turned on using the DIN input, the NMOS switch is turned on and the inductor
V
current ramps up to its peak value, approximately 1600mA nominally.
D A
The current comparator turns off the NMOS switch for a fixed period of time to allow energy to be transferred to the output capacitor. When the voltage on the output capacitor equals or exceeds the desired output voltage, the current loop is disabled until the load discharges the output capacitor to a voltage lower than the desired output voltage. Every time the output voltage falls below the desired value, the switching cycle starts and continues until the desired value is reached. The constant switching resulting in the charging and discharging of the output capacitor causes a ripple on the output voltage. The ripple on the output voltage depends on the external component parameters, such as the value of external capacitor, its ESR, and etc.

In PAM8907, when logic high is asserted on the DIN pin, the boost regulator is enabled. However, the Piezo driver output is not enabled until the output voltage reaches its nominal set point (total soft start time around 1.1ms). This ensures the output voltage rises quickly to the necessary drive voltage for the Piezo. The boost regulator has been optimized to work with the external components as shown in the Typical Application circuit. It is crucial to select an appropriate inductor value for the Boost converter to operate efficiently with expected transient behavior and loop stability under a limited board space condition. 0.68μH to 1.5μH (typical 1.0μH) inductor with saturation current rating of 1A is recommended to optimize PAM8907 performance. PAM8907 6 of 10 May 2021 Document number: DS43314 Rev. 2 - 2
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