PS0021

PS0021 High Efficiency PFM Step-up DC/DC Converter FEATURES PFM control Asynchronous Booster Up to 90% Efficiency Quiescent Supply Current: 5µA Zero Shutdown current Output Voltage Accuracy: ±1% Fixed Output Voltage Provides 20mA from single AAA cell Input Voltage Range: 0.8V to 5.5V Startup Voltage : 0.9V 3L SOT-23 and 6L SOT-26 Package Wireless mice, keyboard Pagers Remote Controls Wireless Headsets Wireless Transmitters Personal Medical Devices Digital Still Cameras MP3/MP4 Players Single-Cell Battery-Powered Devices Low-Power Hand-Held Instruments The PS0021 compact, high-efficiency, step-up DCDC converters are available in tiny, 3-pin thin SOT23 and 6-pin thin SOT26 packages. They feature an extremely low 5µA quiescent supply current to ensure the highest possible light-load efficiency. Optimized for operation from one to two alkaline or nickel-metal-hydride (NiMH) cells, or a single Li+ cell, these devices are ideal for applications where extremely low quiescent current and ultra-small size are critical. The PS0021 also feature proprietary noisereduction circuitry, which suppresses electromagnetic interference (EMI) caused by the inductor in many step-up applications. The family offers different combinations of fixed outputs, shutdown, and EMI reduction (see Selector Guide). Its unique design is optimized for high efficiency at light load condition. DESCRIPTION APPLICATIONS TYPICAL APPLICATION CIRCUIT July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 1 PS0021 PIN CONFIGURATION PIN DESIGNATOR Name SW LBI EN LBO GND VOUT Pin 1 2 3 4 5 6 Type Switch Low–Battery Detector Input. Enable Low Battery Detector Output Ground IC Power Supply Function Connect inductor between SW and Battery. Connect a resistive divider from Battery to LBI to ground. EN=High: normal operation. (Supports both TTL and CMOS Logic). Open–Drain Output. Low–Battery Detector Output is LOW when VLBI is less than 0.6 V. Power Ground VOUT supplies power to Step-up converter. Note 1: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 2: Guaranteed with the addition of a Schottky MBR0520L external diode between LX and OUT when using the PS0021 with only one cell, and assumes a 0.3V voltage drop across the Schottky diode (see Figure 3). Note 3: Supply current is measured with an ammeter between the output and OUT pin. This current correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. Note 4: VOUT forced to the following conditions to inhibit switching: VOUT = 1.05 ✕ VOUT (NOM) VOUT = 3.465V July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 2 PS0021 BLOCK DIAGRAM ABSOLUTE MAXIMUM RATINGS OUT, SHDN, BATT, SW to GND ………………………………………………………………………..................... -0.3V to +6V FB to GND ……………………………………………………………………………………………………….. -0.3V to (VOUT + 0.3V) OUT, SW Current ………………………………………………………........................................................................1A Continuous Power Dissipation (TA = +70°C) 6-Pin Thin SOT26 (derate 7.1mW/°C above +70°C) ……………………………………………………….……….....571mW Operating Temperature Range …………………………………………………………….............................-40°C to +85°C Junction Temperature …………………………………………………………........................................................+150°C Storage Temperature Range ………………………………………………………….................................-65°C to +150°C Lead Temperature (soldering, 10s) ……………………………………………………………………………………………. +300°C July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 3 PS0021 ELECTRICAL CHARACTERISTICS ( VBATT = 1.2V, VOUT = 3.3V, VOUT = VOUT (NOM), SHDN = OUT, RL = ∞, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) Parameter Operating Input Voltage Output Voltage variation Minimum Startup Input Voltage Hold on Voltage Switch leakage N-Channel On-Resistance Maximum oscillating freq Duty ratio Efficiency Quiescent Current into OUT (no switching) Quiescent Current into OUT Shutdown Current into OUT SHDN Voltage Threshold SHDN Input Bias current Symbol VIN VOUT RL= 30kΩ 1 mA load RDS(ON) FOSC DMAX Eff Measured from SW pin voltage and inductor current during SW on time VOUT forced = VOUT (NOM) * 0.95 VOUT forced = VOUT (NOM) * 0.95 VIN= VOUT +0.5V measurement of the IC input current(VOUT pin) (Notes 3, 4) VOUT forced = VOUT (NOM) * 0.95 (Notes 4) En= 0V VIL VIH VSHDN = 5.5V 1.2 0.4 1.1 Conditions ( Note 2 ) Min Typ Max 5.5 3.4 Unit V V V V nA Ω 120 85 KHz % % µA µA µA mV nA 3.2 3.3 0.9 0.7 5 1.4 80 65 100 75 85 5 25 1 Low Battery Detector LBI voltage threshold LBI input hysteresis LBI input current LBO output low voltage LBO output leakage current VOUT forced = VOUT (NOM)*1.05 VOUT forced = VOUT (NOM)*1.05 VOUT forced = VOUT (NOM)*1.05 Force 20mA into LBO LBO= 6.0V 665 15 0.45 670 18 0.02 0.50 0.1 675 22 0.6 mV mV nA V µA July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 4 PS0021 TYPICAL OPERATING CHARACTERISTICS (All specifications are at TA =+25°C, VIN = 1.5V, circuit of typical application circuit, unless otherwise specified.) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 5 PS0021 TYPICAL OPERATING CHARACTERISTICS (continued) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 6 PS0021 TYPICAL OPERATING CHARACTERISTICS (continued) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 7 PS0021 TYPICAL OPERATING CHARACTERISTICS (continued) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 8 PS0021 OPERATION The PS0021 is a compact, high-efficiency, synchronous boost converter in a SOT-26 package designed for spacerestricted applications. The part is available with adjustable output voltages ranging from 2.5V to 5.0V. It is able to start up with input voltages as low as 0.8V and operate with input voltages down to 0.5V. With its internal synchronous rectifier and low on-resistance of the internal NMOS switch, the device maintains high efficiency over a wide range of load current. As shown in the Block Diagram, the PS0021 consists of accurate band gap core, error amplifier, start-up oscillator and control logic unit along with PMOS and NMOS switches. With current mode PWM control, the PS0021 has ultra-fast line and improved load regulation. Moreover, the PS0021 provides real shutdown circuitry which disconnects the output from the input during shutdown and results in the discharge of the output to ground. Thermal overload protection limits the total power dissipation in the PS0021. When the junction temperature exceeds TJ = +145°C, the thermal sensor signals the shutdown logic and turns off most of the internal circuitry. The thermal sensor turns the internal circuitry on again after the IC’s junction temperature drops by 15°C. Thermal overload protection is designed to protect the PS0021 in the event of a fault condition. For continuous operation, do not exceed the absolute maximum junction temperature rating of TJ = +125°C. Thermal Overload Protection Current Limit Protection The PS0021 includes a current limiter that monitors the peak inductor current through the NMOS switch and turns the NMOS switch off when the inductor peak current exceeds 150mA. The PS0021 starts up typically at 0.8V. When it is turned on, the device gets its start up bias from VIN. A start-up oscillator, which runs typically at 650 KHz, takes the output voltage high enough so that VOUT exceeds VIN. Once VOUT exceeds VIN, the internal bias switches from VIN to VOUT by an internal bias-select circuit. Thus, once started (i.e. VOUT exceeds VIN), the internal circuit bias is completely independent of VIN. The start-up oscillator runs at 66% duty cycle at around 650KHz. Once VOUT exceeds VIN (typically 1.9V), the start-up oscillator is disabled and the normal fixed TON PWM operation takes over. Start-Up Mode Light Load Operation The PS0021 provides improved light load efficiency. The internal zero current comparator monitors the inductor current to the load and shuts off the PMOS switch once this current reduces to some low value (typically 50mA). This prevents the inductor current from reversing its polarity, avoiding back-charging and thus improving the efficiency at light loads. At that time, both the NMOS and PMOS switches remain off. However, normal operation starts again when the output voltage falls below the regulation point. The IC automatically skips pulses at light load, thus providing better efficiency. Internal PMOS and NMOS Switches The PS0021 features a 0.45Ω NMOS switch and a 0.6Ω PMOS switch. In normal operation, these switches are alternatively turned on and thus initiate the charging of the inductor from VIN and then discharging of it to the output capacitor and the load. However, between the event of one switch turning off and the other turning on, a dead time is provided to avoid a huge in-rush current from the output to ground via switches. During the dead time, both switches remain off and the inductor discharges via the body diode of the PMOS switch to the output. July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 9 PS0021 Under Voltage Lockout When the supply becomes too low (typically below 1.8V), the PS0021 produces an internal UVLO (Under Voltage Lockout) signal that disables the normal PWM operation and enables the start-up oscillator to run at a fixed frequency. At this stage, very few circuits are operational. When the oscillator raises the supply to above 1.9V, the UVLO signal is disabled and the normal PWM mode takes over the operation of the start-up oscillator. This mechanism protects the chip from producing false logic due to low input supply. The PS0021 features an active-high CMOS input enable pin (SHUTB) that allows on/off control of the regulator. When SHUTB=Low, shutdown of the chip occurs and at that time almost no quiescent current (