The ISL8012 is a high-efficiency, monolithic, synchronous step-down DC/DC converter that can continuously output up to 2A of output current from a 2.7V to 5.5V input supply. It uses a current control architecture that provides extremely low duty cycle operation at high frequency transients with fast response and excellent loop stability. The ISL8012 integrates a pair of low on-resistance P-channel and N-channel internal MOSFETs to maximize efficiency and minimize external component count. 100 % duty cycle at 2A output, operation allows less than 240mV dropout current. A high 1MHz pulse width modulation (PWM) switching frequency allows the use of small external components. The ISL8012 can be configured for discontinuous or forced continuous operation at light loads. Forced continuous operation reduces noise and RFI in discontinuous mode and provides high efficiency loads by reducing optical switching losses. Fault protection is provided by internal current limiting during short circuit and overcurrent conditions, output overvoltage comparators and overtemperature monitoring circuitry. A power commodity output voltage monitor indicates when the output is in regulation. The ISL8012 provides a 1 ms Power Good (PG) timer on power up. During shutdown, the ISL8012 discharges the output capacitor. Other features include internal soft-start, internal compensation, overcurrent protection and thermal shutdown. The ISL8012 is packaged in a space saving 3mmx3mm 10 Ld DFN package in a lead-free package with exposed pad leadframe thermal. The entire converter occupies less than 0.35in2 area.

feature

High Efficiency Synchronous Buck Regulator Efficiency Up to 95%

Good power (PG) output with 1ms delay

2.7V to 5.5V Supply Voltage

3% output accuracy over temperature/load/line

2A guaranteed output current

Start-up with pre-biased output

Internal Soft Start - 1 ms

Soft-stop output discharge during disable

40µA quiescent supply current in PFM mode

Selectable forced pulse width modulation mode and power factor modulation mode

Logic Controlled Shutdown Current Less than 1µA

100% maximum duty cycle

Internal Current Mode Compensation

Peak Current Limit and Hiccup Mode Short-Circuit Protection

Overheating protection

Small 10 Ld 3mmx3mm DFN

Lead Free (RoHS Compliant)

application

DC/DC POL modules

μC/μP, FPGA and DSP power supplies

Plug-in DC/DC modules for routers and switches

Portable Instruments

Test and Measurement Systems

Lithium-ion battery powered equipment

Small Form Factor (SFP) Modules

barcode reader

Absolute Maximum Ratings (referenced to GND) Thermal Information

Vehicle Identification Number, VCC. -0.3V to 6V

EN, RSI, PG. -0.3V to VIN +0.3V

LX. -1.5V (100 ns)/-0.3V (DC) to 6.5V

Ventricular fibrillation. -0.3V to 2.7V

Recommended Operating Conditions

VIN supply voltage range. 2.7V to 5.5V

load current range. 0A to 2A

Ambient temperature range. -40°C to +85°C

Electrostatic discharge rating

mannequin. 5 kV

machine type. 300 volts

Thermal resistance (typ.) θJA (°C/W) θJC (°C/W)

10 Ld 3x3 DFN (Note 4, 5). 49 5.5

junction temperature range. -55°C to +125°C

Storage temperature range. -65°C to +150°C lead-free reflow profile.

NOTE: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to these conditions may adversely affect product reliability, resulting in failures not covered under warranty.

notes:

4. θJA is measured in free air with components mounted on a highly efficient thermally conductive test board with "direct connect" capability.

5. For θJC, the "case temperature" location is the center of the exposed metal pad on the bottom of the package.

Electrical Specifications, unless otherwise noted, all parameter limits are determined at recommended operating conditions and typical specifications are measured at: TA=-40°C to +85°C, VIN=3.6V, EN=VCC ,Unless otherwise indicated. Typical values are at TA=+25°C. Blackbody limits apply over -40°C to +85°C operating temperature range

Electrical Specifications, unless otherwise noted, all parameter limits are determined at recommended operating conditions and typical specifications are measured at: TA=-40°C to +85°C, VIN=3.6V, EN=VCC ,Unless otherwise indicated. Typical values are at TA=+25°C. Blackbody limits apply over the operating temperature range, -40°C to +85°C. (continued)

notes:

6. Limits determined by characterization, no production testing.

7. Unless otherwise specified, parameters with minimum and/or maximum limits are 100% tested at +25°C. Temperature limits determined by characterization are also not production testing.

Typical Operating Performance (Unless otherwise stated, operating conditions are: TA=+25°C, VVIN=2.5V to 5.5V, EN=VIN, Mode=0V, L=2.2µH, C1=2x10µF, C2= 2x10µF, IOUT=0A to 2A).

Typical Operating Performance (Unless otherwise stated, operating conditions are: TA=+25°C, VVIN=2.5V to 5.5V, EN=VIN, Mode=0V, L=2.2µH, C1=2x10µF, C2= 2x10µF, IOUT=0A to 2A). (continued)

theory of operation

The ISL8012 is a step-down switching regulator for battery powered handheld applications. The regulator's fixed switching frequency of 1MHz under heavy load conditions allows the use of small external inductors and capacitors with minimal printed circuit board (PCB) area. At light loads, the regulator reduces the switching frequency (unless forced to frequency) to minimize switching losses and maximize battery life. Quiescent current when the output is unloaded is typically only 40µA. when the regulator is off. The PWM control scheme pulling the MODE pin low (<0.4V) will force the converter into PWM mode, independent of the output current. The ISL8012 uses a current-mode pulse width modulation (PWM) control scheme for fast transient response and pulse-by-pulse current limiting. Figure 2 shows the block diagram. The current loop consists of oscillator, PWM comparator, current sensing circuit and slope current loop stability compensation. The current gain sense circuit is typically 285mV/A The current loop comes from the output of the error amplifier (EAMP). The pulse width modulation operation is initiated by the oscillator's clock. This P-channel MOSFET turns on the current in the MOSFET at the beginning of the PWM cycle and starts to rise. When the current amplifier CSA and slope compensation (675mV/μs) reach the control reference of the current loop, the comparator COMP sends a signal to the PWM logic to turn off the P-MOSFET and turn on the N-channel MOSFET. The N-MOSFET remains on until the end of the PWM period. Figure 32 shows the operating waveforms during a typical PWM operation. The dashed lines illustrate the slope compensation ramp and the CSA output of the current sense amplifier. The output voltage is regulated to the current cycle by controlling the VEAMP voltage. The bandgap circuit outputs the voltage of the 0.8V reference voltage loop. The feedback signal comes from the VFB pin. The soft-start block affects startup only and will be discussed separately.

The error amplifier is a transconductance amplifier current output that converts the voltage error signal. The voltage loop internal compensation uses 27pF and 390kRC network. The maximum EAMP voltage output is precisely fixed at 1.47V. Skip Mode Pulling the MODE pin high (>1.4V) will force the converter into PFM mode. The ISL8012 enters pulse skip mode at light loads to reduce switching losses by reducing the switching frequency. Figure illustrates skip mode operation. The zero-cross sensing circuit shown in Figure 2 monitors the N-MOSFET current for zero-crossing. When the inductor detects a current zero crossing for 8 consecutive cycles, the regulator enters trip mode. During 8 detection cycles, the current in the inductor is allowed to become negative. When the current does not cross zero in any cycle. Once in skip mode, pulse modulation begins to be controlled by the skip comparator shown in Figure 2. Each pulse period is still synchronized by the PWM clock. The P-MOSFET is turned on on the rising edge of the clock, skipping the current limit when the output is 1.5% above nominal or when its current peaks. The inductor current then discharges to zero amps and remains there. The internal clock is disabled. Due to the load, the output voltage gradually reduces the output capacitor discharge current. When the output voltage drops to the rated voltage, the P-MOSFET will turn on again to repeat the last clock operation on the rising edge of the internal clock. When the output voltage is 1.5% lower than the rated voltage.

Mode control

The ISL8012 has a mode pin that controls the mode of operation. The regulator operates in forced PWM mode when the MODE pin is driven low or shorted to ground. Forced PWM mode maintains a fixed PWM frequency at light loads instead of entering skip mode. Overcurrent Protection Overcurrent protection is achieved by monitoring the CSA output with the OCP comparator, as shown in Figure 2. The current sense circuit has a gain of 285mV/a from the P-MOSFET current to the CSA output. When the CSA output reaches 1V, which is equivalent to 2.9A of switch current (0.15V offset), the OCP comparator trips to immediately turn off the P-MOSFET. This overcurrent function protects the switching converter from monitoring the flow through the upper MOSFET. Once an overcurrent condition is detected, the upper MOSFET turns off immediately until the next switching cycle. Short-Circuit Protection The Short-Circuit Protection SCP comparator monitors the VFB pin output short-circuit protection voltage. When VFB is lower than 0.2V, the SCP comparator forces the PWM oscillator frequency down to a minimum value to reduce power dissipation. The comparator is activated or output short circuit event. When the RSI/PG function is energized, the open collector power good output remains low for about 1ms after VO reaches the preset voltage. When the active high reset signal RSI is issued, PG goes low immediately after RSI returns to low. The output voltage is not affected. Please refer to the chart in the time chart. When not using this feature, connect RSI to ground and keep pull-up resistor R4 open at the PG pin. The PG output is also used as a 1ms delayed power good signal when pull-up resistor R1 is installed. The RSI pin needs to be grounded directly (or indirectly through a resistor) PG will actively monitor the output voltage.

soft start

Soft-start reduces inrush current during startup. soft-start block to the error amplifier. This voltage ramp limits the inductor current as well as the speed of the output voltage, allowing the output voltage to rise in a controlled manner. When soft-start begins when VFB is below 0.2V, the switching frequency is reduced to 1/3 of the nominal value, so that the start-up output is smooth at light loads. During soft-start, the IC operates in skip mode to support pre-biased output conditions. The Enable Enable (EN) input allows the user to control turning the regulator on or off for purposes such as power-up sequencing. When the regulator is enabled, there is typically a 600-µs delay to wake up the bandgap reference and then soft-start begins. Discharge mode (soft stop) is set when switching to shutdown mode or vehicle identification number (VIN) low voltage, the output switches through the internal 100 discharge to GND. Power MOSFET power MOSFETs are optimized for best efficiency. The on-resistance of this P-MOSFET is typically 120m, and the on-resistance of the N-MOSFET is typically 110m. 100% Duty Cycle The ISL8012 features 100% duty cycle operation to maximize battery life. The regulating regulator fully turns on the P-MOSFET when the battery voltage drops to the point where the ISL8012 can no longer maintain the output. The maximum voltage drop at 100% duty cycle operation is the load current and the P-MOSFET. Thermal Shutdown The ISL8012 has built-in thermal protection. When the internal temperature reaches +140°C, the regulator shuts down completely. When the temperature drops to +115°C, the ISL8012 resumes operation by single-stepping the soft-start operation. Application Information Output Inductor and Capacitor Selection Considering steady-state and transient operation, the ISL8012 typically uses a 2.2µH output inductor. High and low inductance values can be used to optimize overall converter system performance. For example, for higher output voltage 3.3V applications, to reduce the inductor current ripple and output voltage ripple, the output inductor value can be increased. It is recommended to set the ripple inductor current to about 30% of the maximum output current for optimal performance. The inductor ripple current can be expressed as Equation 1:

The saturation current rating of the inductor needs to be at least greater than the peak current. The ISL8012 protects a typical peak current of 3A. Saturation current needs to be greater than the 4A maximum output current application. The ISL8012 uses an internal compensation network and the output capacitor value depends on the output voltage. Ceramic recommended capacitors are X5R or X7R. Recommended minimum output capacitor values for X5R or X7R are shown in Table 1.

In Table 1, different output voltages are given to ensure that the entire converter system is stable. The maximum output capacitor should be limited to 50µF or less. The output voltage of the output voltage selection regulator can be passed through an external resistor divider, which is used to measure the output voltage relative to the internal reference voltage and fed back to the inverting input of the error amplifier. See Figure 1. The output voltage programming resistor R3 will depend on the value selected for the feedback resistor and the voltage of the desired output regulator. The value of the feedback resistor is typically between 10k and 100k, as shown in Equation 2.

If the desired output voltage is 0.8V, R3 is not welcome shorted to R2. For better performance, add a 220pF band R2 (124k input capacitor) in parallel. The main function of the input capacitor is decoupling and filtering of parasitic inductance to prevent switching current from flowing back to the battery rail. Two 10µF X5R or X7R ceramic capacitors are a good The starting point for input capacitor selection. Layout Recommendations Layout is a very important step in converter design to ensure that the designed converter works well. For the ISL8012 the power loop consists of the output inductor L, the output capacitor COUT, the LX pin and SGND Pins. It is necessary to keep the power loop as small as possible. The heat of the IC is dissipated mainly through the thermal pad. It is better to maximize the copper area connected to the thermal epad. Also, have a solid ground on the second layer for EMI performance helps. Then connect the epad to a ground plane with at least 5 vias for best thermal performance