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RP901K Series

Synchronous Step-down DC/DC Converter with VD and VR

Data Sheet / Flyer


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The RP901xxxx is a CMOS-based current mode PWM control synchronous step-down DC/DC converter with a voltage detector (VD) and an LDO regulator (VR).

Each of Step-down DC/DC converters is composed of an oscillator, a voltage reference unit, an error amplifier, a switching control circuit, a soft-start circuit, a protection circuit, a UVLO circuit, a switching transistor. Due to the switching elements are built in and synchronous control, a high efficiency step-down DC/DC converter can be made with an inductor and capacitors. To realize high efficiency at light load, automatic PWM/VFM alternative mode can be selected other than the PWM fixed control mode.

As protection circuits, a current limit circuit which limits Lx peak current cycle by cycle and a hiccup mode protection circuit which works if the load current over the limit continues for a certain time^*1 are built in. The output voltage can be preset with 0.05V step in the factory due to the built-in feed back resistance, and the tolerance is ±2%. Since the package is DFN (PLP) 2527-10, high density mounting on board is possible.

Built-in LDO regulator (VR) is composed of a voltage reference unit, a voltage detecting resistor-network, an error amplifier, a short current limit circuit, and a driver transistor. After the soft-start time of the DC/DC converter is over and a specified delay time, LDO starts up. The sequence function is fixed internally^*2.

Built-in voltage detector (VD) supervises the input voltage or the output of the VR (The reset function works for UVLO and over-current of the DC/DC converter). The option is preset in the factory. The output type is N-channel open drain. The released delay time is built-in, typ.50ms.

If the junction temperature of the IC is over the limit, the system is reset by the built-in thermal shut-down circuit.

*1 A version: As soon as the load current is over the limit, the system restarts by the protection.
*2 C, D versions: No sequence function

Input Voltage Range		4.5V to 5.5V
Supply Current		Typ. 460µA (at PWM mode) Typ. 170µA (at light load applied to B, C, D versions)
Step-down DC/DC Converter
	Output Voltage Range	1.2V to 1.8V, preset is possible by user's request
	Output Voltage Tolerance	±2%
	Oscillator Frequency	Typ. 1.2MHz
	Built-in driver ON resistance	Typ. P-channel 0.25Ω, N-channel 0.25Ω (at VIN=5V)
	Soft-start function	Typ. 1ms
	Lx peak current limit function	Typ. 1.4A (D version: 1.5A)
	Output Current	Min. 800mA (D version: 900mA)
	Protection Delay Time	Typ. 0.1ms (applied to B, C, D versions)
	UVLO function	Typ. 3.5V
	Chip enable function	"H" active
LDO Regulator
	Output Voltage Range	2.5V to 3.3V, preset is possible by user's request
	Output Voltage Tolerance	±1.0%
	Output Current	Min. 600mA
	Start-up delay time	Typ. 2ms (applied to A, B versions)
	Auto-Discharge function at turning off	Discharge resistance Typ.50Ω (at VIN=5V)
VD
	Voltage Detector Threshold Range	2.0V to 3.0V, preset is possible by user's request (A version: VR output voltage is supervised), 3.0V to 5.0V, preset is possible by user's request (B, C, D versions: Input voltage is supervised)
	Released Delay Time	Typ.50ms
Thermal shutdown circuit		Typ.50, Detecting Temperature: Typ. 165°C, Released temperature: Typ. 110°C
Package		DFN(PLP)2527-10
External Components		CIN: 10.0µF, COUT1=10.0μF, L=4.7µH (DC/DC), COUT2=2.2µF(VR)